PROJECT 4: HATCHERY TROUT EVALUATIONS...catchables across 24 Idaho lakes and reservoirs and 19...

PROJECT 4: HATCHERY TROUT EVALUATIONS

Grant # F-73-R-40

Report Period July 1, 2017 to June 30, 2018

Phil Branigan Senior Fisheries Research Biologist

IDFG Report Number 18-16 July 2018

Annual Performance Report

July 1, 2017 to June 30, 2018

Grant # F-73-R-40

Project 4: Hatchery Trout Evaluations

Subproject #1: Improving Returns of Hatchery Catchable Rainbow Trout Including Evaluations of Statewide Exploitation Rates, Magnum versus Standard Catchable

Releases, and Raceway Baffles

Subproject #2: Relative Performance of Triploid Kokanee Salmon in Idaho Lakes and Reservoirs

Subproject #3: Performance of Diploid and Triploid Westslope Cutthroat Trout

Stocked into Idaho Alpine Lakes

By

Phil Branigan

Idaho Department of Fish and Game 600 South Walnut Street

P.O. Box 25 Boise, ID 83707

IDFG Report Number 18-16 July 2018

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TABLE OF CONTENTS Page

ANNUAL PERFORMANCE REPORT ......................................................................................... 1 SUBPROJECT #1: IMPROVING RETURNS OF HATCHERY CATCHABLE RAINBOW

TROUT INCLUDING EVALUATIONS OF STATEWIDE EXPLOITATION RATES, MAGNUM VERSUS STANDARD CATCHABLE RELEASES, AND RACEWAY BAFFLES .............................................................................................................................. 1

ABSTRACT ................................................................................................................................. 1 INTRODUCTION ........................................................................................................................ 2

Study Questions ....................................................................................................................... 3 METHODS .................................................................................................................................. 4

Stocking Years 2015 and 2016 Statewide Exploitation ............................................................. 4 Magnum Rearing ..................................................................................................................... 4 Baffled Raceway ...................................................................................................................... 4 Tagging and Stocking .............................................................................................................. 4 Data Analysis ........................................................................................................................... 5

RESULTS ................................................................................................................................... 6 Stocking Years 2015 and 2016 Statewide Exploitation ............................................................. 6 Magnum Rearing ..................................................................................................................... 6

Lakes and Reservoirs ............................................................................................................ 6 Flowing Waters ..................................................................................................................... 7

Baffled Raceway ...................................................................................................................... 7 Tag Reporting Rate .................................................................................................................. 7

DISCUSSION.............................................................................................................................. 7 Stocking Years 2015 and 2016 Statewide Exploitation ............................................................. 7 Magnum Rearing ..................................................................................................................... 7 Baffled Raceway ...................................................................................................................... 8 Tag Reporting Rate .................................................................................................................. 8

FUTURE RESEARCH AND MANAGEMENT RECOMMENDATIONS ........................................ 8 ACKNOWLEDGEMENTS ......................................................................................................... 10 LITERATURE CITED ................................................................................................................ 11 ANNUAL PERFORMANCE REPORT ....................................................................................... 30 SUBPROJECT #2: RELATIVE PERFORMANCE OF TRIPLOID KOKANEE SALMON IN

IDAHO LAKES AND RESERVOIRS .................................................................................... 30 ABSTRACT ............................................................................................................................... 30 INTRODUCTION ...................................................................................................................... 31 OBJECTIVES ........................................................................................................................... 32 METHODS ................................................................................................................................ 32

Study Sites ............................................................................................................................. 32 Egg Collection and Triploidy Induction ................................................................................... 32 Hatchery Rearing and Stocking .............................................................................................. 32 Fish Sampling ........................................................................................................................ 33 Data Analysis ......................................................................................................................... 33

PRELIMINARY RESULTS / DISCUSSION ............................................................................... 33

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ACKNOWLEDGEMENTS ......................................................................................................... 35 LITERATURE CITED ................................................................................................................ 36 ANNUAL PERFORMANCE REPORT ....................................................................................... 40 SUBPROJECT #3: PERFORMANCE OF DIPLOID AND TRIPLOID WESTSLOPE

CUTTHROAT TROUT STOCKED INTO IDAHO ALPINE LAKES ....................................... 40 ABSTRACT ............................................................................................................................... 40 INTRODUCTION ...................................................................................................................... 41 METHODS ................................................................................................................................ 42

Triploid Recipe Development ................................................................................................. 42 Egg Collection / Rearing ........................................................................................................ 42 Post-Stocking Evaluation ....................................................................................................... 43 Genetic Analyses ................................................................................................................... 44 Data Analyses ........................................................................................................................ 44

RESULTS ................................................................................................................................. 45 Triploid Recipe Development ................................................................................................. 45 Egg Collection / Rearing ........................................................................................................ 45 Post-Stocking Evaluation ....................................................................................................... 45

DISCUSSION............................................................................................................................ 46 ACKNOWLEDGMENTS ............................................................................................................ 49 LITERATURE CITED ................................................................................................................ 50

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LIST OF TABLES Page

Table 1. Waters that were stocked with tagged catchables in 2015 along with the

total number of catchables stocked in those waters for the calendar year. ......... 13 Table 2. Total nonreward tags released by water body, hatchery, stocking date, and

treatment in 2015. Harvest and Catch were estimated through the first year at large with associated 90% confidence intervals (C.I.). .................................... 14

Table 3. Waters that were stocked with tagged catchables in 2016 along with the total number of catchables stocked in those waters for the calendar year. ......... 18

Table 4. Total nonreward tags released by water body, hatchery, stocking date, and treatment in 2016. Harvest and Catch were estimated through the first year at large with associated 90% confidence intervals (C.I.). .................................... 19

Table 5. Total nonreward tags released by water body, hatchery, stocking date, and treatment in 2015. Harvest and Catch were estimated through the second year at large with associated 90% confidence intervals (C.I.). ............................ 22

Table 6. Total nonreward tags released by water body, hatchery, stocking date, and treatment in 2016. Harvest and Catch were estimated through the second year at large with associated 90% confidence intervals (C.I.). ............................ 23

Table 7. Catch rates for catchable Rainbow Trout reared in baffled and unbaffled raceways at Nampa Fish Hatchery and stocked in 2017. Catch estimates are categorized by water body type and represent tags returned within the first year at-large. ............................................................................................... 24

Table 8. Net-hours, CPUE, and age distribution of diploid (2N) and triploid (3N) Kokanee Salmon in two control and two treatment lakes for sample years 2012-2017. Gray shaded values represent age classes that are triploid. ........... 37

Table 9. Means and ranges of lake and fish characteristics measured at 51 alpine lakes in Idaho where either diploid or mixed-sex triploid Westslope Cutthroat Trout were stocked and sampled three years later. CPUE is catch-per-unit-effort (fish/hr), and Wr is relative weight. ...................................... 54

Table 10. Percent eye-up and percent triploidy (with upper and lower 95% confident intervals) for controls and three pressure treatments of fertilized Westslope Cutthroat Trout eggs treated at 9,500 for 5 minutes at varying Celsius-minutes-after-fertilization (CMAF). ..................................................................... 54

Table 11. Model results relating catch-per-unit-effort (CPUE), fish length, and relative weight of test fish to various lake and fish characteristics at 51 alpine lakes in Idaho stocked with either diploid or mixed-sex triploid Westslope Cutthroat Trout fry and sampled three years later. ............................................. 55

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LIST OF FIGURES Page

Figure 1. A.) Design of a 3.6-m aluminum baffle installed at Nampa Fish Hatchery.

Each baffle was installed perpendicular to flow and a 13 mm gap was maintained between the bottom edge of the baffle and the raceway floor to increase current velocity and transport waste material. Two openings (61 × 15 cm) were cut along the bottom edge of each baffle to allow fish to move freely within the raceway. B.) Side view of baffle installed into raceway, illustrating the 70° angle created between the back of the baffle and the raceway floor. ........................................................................................ 25

Figure 2. Catch rates for magnum (total length = 305 mm) and standard (total length = 254 mm) catchables stocked into lakes, reservoirs, and flowing waters across Idaho between 2014 and 2016. Catch was estimated through the first year at-large (i.e., within 365 days of release). ............................................ 26

Figure 3. Catch rates for magnum (total length = 305 mm) and standard (total length = 254 mm) catchables stocked into lakes, reservoirs, and flowing waters across Idaho between 2014 and 2016. Catch was estimated through the second year at-large (i.e., between 366-730 days of release). No tags were returned during the second year at-large for flowing waters in 2015................... 27

Figure 4. Catch rates for catchable Rainbow Trout reared in baffled and unbaffled raceways at Nampa Fish Hatchery. Fish were stocked in late spring and early summer of 2017 into ponds, lakes, reservoirs, and flowing waters across Idaho. Estimated catch for Heroes pond exceeds 100% due to inherently high catch of tagged fish and a correction factor applied during calculation (see methods). ................................................................................. 28

Figure 5. Year-specific angler tag reporting rates. Note: 2017 is a preliminary reporting rate. .................................................................................................... 29

Figure 6. Relative abundance (fish/net hr) of Kokanee Salmon sampled from 2012-2017 among four study waters. .......................................................................... 38

Figure 7. Length distribution (by percent) of Kokanee Salmon across four water bodies. Distributions represent samples taken in the summer of 2012-2017. .......................................................................................................................... 39

Figure 8. Relative weights of juvenile diploid (2N) and mixed-sex triploid (3N) Westslope Cutthroat Trout prior to stocking in 2011 and 2013. .......................... 56

Figure 9. Scatterplots of potential density-dependent relationships for catch-per-unit-effort, mean length, and relative weight (Wr) for diploid (open circles) and mixed-sex triploid (filled circles) Westslope Cutthroat Trout stocked in 51 alpine lakes in Idaho and sampled three years later. Correlation coefficients (r) and least-squares linear regression lines are also depicted. .......................... 57

Figure 10. Sex composition of diploid and triploid Westslope Cutthroat Trout stocked in 51 alpine lakes in Idaho in 2013 and sampled three years later. .................... 58

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ANNUAL PERFORMANCE REPORT SUBPROJECT #1: IMPROVING RETURNS OF HATCHERY CATCHABLE RAINBOW

TROUT INCLUDING EVALUATIONS OF STATEWIDE EXPLOITATION RATES, MAGNUM VERSUS STANDARD CATCHABLE RELEASES, AND RACEWAY BAFFLES

State of: Idaho Grant No.: F-73-R-40 Fishery Research Project No.: 4 Title: Hatchery Trout Evaluations Subproject #1: Improving Returns of Hatchery

Catchable Rainbow Trout Contract Period: July 1, 2017 to June 30, 2018

ABSTRACT

Idaho Department of Fish and Game (IDFG) hatcheries are integral to managing coldwater sportfishing opportunities in Idaho. A comprehensive evaluation of hatchery catchable trout exploitation rates in Idaho’s put-and-take fisheries was identified as a need and initiated in 2011. This project was intended to (1) evaluate catch and harvest rates of the most-stocked waters statewide, and (2) conduct research focusing on hatchery rearing techniques to increase return-to-creel of catchable Rainbow Trout Oncorhynchus mykiss. Since 2011, IDFG has released over 200,000 T-bar anchor tagged trout to evaluate returns of stocked catchables to anglers. Research specific to hatchery rearing techniques currently includes studies of magnum (305 to 320 mm, average) vs. standard (254 mm average) sized catchables and baffled vs. non-baffled raceways. This report serves as an update for tag years 2015-2017. For all tags released in 2015 and reported within 365 days of release, average harvest for catchable Rainbow Trout across all evaluated waters was 19.1% (± 1.9%), and average total catch was 26.3% (± 2.5%). Similar values were observed for tag year 2016, where average harvest was estimated as 18.2% (± 2.0%) and average total catch was 24.6% (± 2.5%). Magnum catchables were released alongside standard catchables across 24 Idaho lakes and reservoirs and 19 flowing waters. Magnums showed a 107% increase in return-to-creel over standard catchables for fish stocked into lakes and reservoirs. Magnums in flowing waters performed similarly, and showed a 53% increase in return-to-creel over standard catchables. Fish reared in a baffled raceway have not shown an appreciable performance benefit when stocked into lakes, reservoirs, or flowing waters. In ponds, fish reared in a baffled raceway were caught at an 8% lower rate than fish reared in a standard, unbaffled raceway. When considering these findings, managers must also consider the balance between angler catch, effort, and satisfaction as they work towards maximizing the benefit to anglers from put-and-take fisheries.

Author: Phil Branigan Senior Fisheries Research Biologist

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INTRODUCTION

Idaho Department of Fish and Game (IDFG) hatcheries are integral to managing coldwater sportfishing opportunities in Idaho. IDFG’s “resident” (non-anadromous) hatchery program consists of 10 hatcheries that raise up to 18 strains of salmonids for inland coldwater fisheries. In 2016, Idaho hatcheries stocked over 18 million resident fish, including over 2 million catchable-sized (254 mm total length; henceforth, “catchables”) Rainbow Trout Oncorhynchus mykiss. Producing catchables accounts for over 50% of the annual resident hatchery budget. Nampa and American Falls fish hatcheries produce the majority of IDFG catchables. According to the default catchables stocking request list, Rainbow Trout are planted in approximately 290 waters throughout Idaho. Catchables have become an important component of many fisheries management programs in coldwater habitats because they provide instantaneous fisheries once they are stocked. This is especially important in altered habitats such as impounded reservoirs, which typically do not support wild trout populations, and often do not provide adequate conditions over a sufficient time period for put-and-grow fisheries to develop (Trushenski et al. 2010).

In recent years, hatchery rearing and transport costs have increased while funding for

general hatchery operations has not. Considering the higher costs associated with stocking catchable trout, the need to identify factors contributing to angler catch of hatchery catchables was identified. Accordingly, a comprehensive evaluation in Idaho’s predominant put-and-take fisheries was initiated. Recent IDFG studies have evaluated return-to-creel on a statewide basis using angler-caught tagged fish (e.g., Meyer et al. 2012; Cassinelli and Koenig 2013; Cassinelli 2014, 2015, 2016; Cassinelli and Meyer 2018). These studies evaluated angler catch of hatchery catchable trout that were reared under a variety of conditions and stocked across numerous waters throughout Idaho. However, continued efforts to optimize hatchery production are of high priority and require continued research to ensure that hatchery programs remain efficient while producing a quality product for Idaho anglers.

One of the key metrics defining a “quality” hatchery trout should be the contribution to

angler return-to-creel (catch or harvest). Numerous factors have been shown to influence post-stocking performance of catchable trout, including water temperature, size, species composition, elevation, and abiotic components of the water being stocked. In addition, hauling distance from the hatchery, fish size-at-stocking, stocking season, stocking density, and hatchery feed formulation have also been shown to influence post-stocking performance of catchable trout (e.g., Wiley et al. 1993; Yule et al. 2000; Barnes et al. 2009; Koenig and Meyer 2011; Ashe et al. 2014; Cassinelli et al. 2016). Although these factors can affect post-stocking performance, hatchery staff and fisheries managers are unable to control all factors that influence angler return-to-creel rates. Nevertheless, it is valuable to understand the effects such factors have on post-release performance, regardless of the level of control that can be exerted on them.

In addition to understanding the factors that influence return-to-creel, it is also important

for managers to better understand what factors might influence the longevity of catchable fisheries. For example, if a desirable percentage of the stocked trout are caught by anglers but all of the catch occurs in a short period of time post-stocking, receiving waters may require more frequent stocking to maintain return rates acceptable to anglers. Decisions about effective allocation of catchable trout could subsequently improve the efficiency of the resident hatchery system and directly benefit anglers by increasing return-to-creel. This type of monitoring and evaluation program is critical in the decision-making process of allocating catchable production.

While several factors may contribute to the overall return rate of catchables, hatchery-

rearing techniques may similarly affect post-stocking performance. For example, previous studies

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have shown a strong correlation between increased size-at-release and increased return-to-creel for hatchery trout (Mullan 1956; Wiley et al. 1993; Yule et al. 2000; Cassinelli 2015; Cassinelli 2016). The current target length for a catchable trout released from an IDFG hatchery is variable, from 254 to 305 mm, depending on the receiving water. Although larger trout may return to the creel at a higher rate, rearing fish to a larger size comes with significant increases in rearing time, space, and cost. Therefore, it is important to find a balance between size-at-release, hatchery infrastructure, rearing costs, and return-to-creel.

Hatchery rearing techniques may serve to optimize routine hatchery operations while

improving return-to-creel. Raceway baffles were first described as a means to improve cleaning efficiencies and reduce solid waste in raceways. Baffles installed throughout the length of a raceway, that are spaced approximately equal to the width of the raceway and contain a small gap between the bottom of the baffle and raceway floor, will increase current velocity along the bottom of the raceway (Boersen and Westers 1986). Consequently, waste products are moved towards the outflow, reducing the need for frequent cleaning by hatchery personnel (Kindschi et al. 1991). The variable current velocities and microhabitats created by raceway baffles may provide a rearing environment more similar to that of natural conditions. As such, fish stocked from baffled raceways may exhibit improved survival and return-to-creel rates than fish reared in standard, unbaffled raceways.

Study Questions

This project consists of two major components: (1) an evaluation of catch and harvest rates at select waters, and (2) investigations on the effects of hatchery rearing techniques on total catch of stocked catchable trout in Idaho. The following outlines the goals and objectives of these major components.

1. Catch and Harvest Rate:

Allocate hatchery resources to maximize benefits to anglers from catchable hatchery

Rainbow Trout stocked in Idaho waters.

Objective: • Determine the average catch and harvest rates of catchable Rainbow Trout in

various water bodies for release years 2015 and 2016.

2. Hatchery Rearing Techniques:

Optimize hatchery production by modifying rearing practices to maximize catch and harvest rates.

Objectives: • Evaluate the total catch benefit from releasing magnum-sized catchables (average

size 305 mm) vs. standard-sized catchables (average size 254 mm).

• Evaluate total catch of Rainbow Trout that are reared in baffled vs. standard (i.e., unbaffled) raceways.

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METHODS

Catchables were raised from 2014 to 2017 from eggs either purchased from Troutlodge, Inc. (all-female triploids) or fertilized internally from IDFG’s Hayspur strain (mixed-sex triploids). These two egg sources provide nearly all of the Rainbow Trout eggs used in the IDFG resident hatchery program.

Stocking Years 2015 and 2016 Statewide Exploitation

The most recent stocking years with sufficient time-at-large to be fully evaluated for this report are 2015 and 2016. Previous stocking year-specific (2011-2014) angler return information can be found in previous reports (Cassinelli and Koenig 2013; Cassinelli 2014; Cassinelli 2015; Cassinelli 2016; Cassinelli and Meyer 2018).

Magnum Rearing

In addition to evaluating statewide exploitation, we evaluated the relationship between size-at-release and subsequent catch. “Magnum” catchables (target size = 305 mm) were evaluated between 2014 and 2016 at American Falls and Nampa fish hatcheries. Lakes and reservoirs were evaluated in 2014 and 2015, whereas flowing waters were evaluated in 2015 and 2016. Magnum catchables were stocked alongside equal numbers of standard catchables throughout the evaluation.

Baffled Raceway

Raceway baffles were installed into a single raceway at Nampa Fish Hatchery to evaluate the effect on return-to-creel of catchable Rainbow Trout. Nine aluminum baffles, spaced 3.7 m apart, were installed perpendicular to flow along a 36.6-m raceway and positioned at a 70° angle to the raceway floor. A 13 mm gap was maintained between the bottom edge of each baffle and the raceway floor to increase current velocity and transport waste material. In addition, two openings (61 × 15 cm) were cut along the bottom edge of each baffle to allow fish to move freely within the raceway (Figure 1). Fish were reared alongside a standard control (i.e., unbaffled) raceway, and both groups were reared to catchable size (target of 254 mm [total length] at time of stocking) in outdoor concrete raceways on 13-15°C single-use spring water. Rearing conditions such as feeding, inventorying, and raceway density were identical for both raceways.

Tagging and Stocking

All catchables were tagged prior to stocking with 70 mm fluorescent orange T-bar anchor tags. Fish were collected for tagging by crowding them within raceways and capturing them with dip nets. This ensured a representative sample was collected from the entire raceway. Fish were sedated, measured to the nearest mm (total length), and tagged just under the dorsal fin following the methods of Guy et al. (1996). After tagging, fish were returned to an empty section of raceway, or to a holding pen in the raceway, for at least 12 hours. Within 48 hours of tagging, tagged fish were loaded by dip net onto stocking trucks and transported to stocking locations. Tags were implanted into fish at 10% of the total number of catchables requested for a particular water body, and no more than 500 tags were stocked in one release group. Mortalities and shed tags were rare (<1%), and were collected and recorded prior to loading fish for transport. Some waters were stocked with tagged fish only once per calendar year while others were stocked multiple times depending on the popularity and general use of the water body. Stocking events occurred from March through November annually.

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The return-to-creel and days-at-large data were obtained using information provided by

anglers who reported their catch. Anglers could report tags using the IDFG (Tag! You’re It!) phone system or website (set up specifically for this program), as well as at regional IDFG offices or by mail. To facilitate angler reporting of tagged fish, anchor tags were labeled with “IDFG”, a tag reporting phone number, and website on one side, and a unique tag number on the reverse side. Each year, a subset of study waters received $50 reward tags in addition to standard nonreward tags. In locations that received reward tags, rewards were distributed at a constant rate of 10% of the total tags stocked. Reward tags were identical to nonreward tags in size, shape, and color, but contained additional text (“Reward”) and the reward amount (“$50”). For a more detailed description of the angler tag reporting system used, see Meyer et al. (2012) and Meyer and Schill (2014).

Data Analysis

To estimate the angler tag reporting rate (λ) of nonreward tags, I used the high-reward method (Pollock et al. 2001) and equation:

NtNrRtRr

//

=λ

where Rt and Rr are the number of nonreward tags stocked and reported, respectively, and Nt and Nr are the number of reward tags stocked and reported, respectively. A correction factor was applied to this equation to account for the fact that an estimated 88% of $50 tags are actually reported (Meyer et al. 2012). The year-specific tag reporting rate, calculated by pooling tags from all waters that received reward tags within a given stocking year, was used to correct angler return rates at all waters for that stocking year. Year-specific catch and harvest estimates were then calculated using the appropriate year-specific reporting rate.

In each study year, a subsample of catchables was double tagged to calculate tag loss rates. Double-tagged fish received two tags implanted next to each other on the same side of the fish. All anglers returning tags were asked if the fish they caught was tagged with one or two tags. Any double-tagged fish that lost a tag were used to calculate tag shedding rates following the methods of Meyer and Schill (2014).

Harvest was calculated within the first year (365 days) and the second year (366-730

days) after stocking, following the methods of Meyer et al. (2012). The annual unadjusted harvest rate (u) was calculated as the number of nonreward tagged fish reported as harvested within one year of tagging, divided by the number of nonreward tags released. Unadjusted harvest and total catch were adjusted (uʹ) by incorporating the average angler tag reporting rate (λ), first year tag loss (Tagl), and tagging mortality (Tagm) for Rainbow Trout tagged as part of this study. Estimates were calculated for each individual stocking event using the formula:

𝑢𝑢′ =

𝑢𝑢𝜆𝜆(1 − 𝑇𝑇𝑇𝑇𝑇𝑇𝑙𝑙)(1 − 𝑇𝑇𝑇𝑇𝑇𝑇𝑚𝑚)

Variance for the denominator in the above equation was estimated using the approximate

formula for the variance of a product in Yates (1953). Variance for uʹ was calculated using the approximate formula for the variance of a ratio (Yates 1953) and was used to derive 90% confidence intervals (CIs). A more complete description of these methods and the associated formulas is described in Meyer et al. (2012).

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Some anglers release fish voluntarily; as such, harvest estimates may not accurately

characterize the utilization of hatchery fish by anglers (Quinn 1996). To account for catch-and-release in addition to harvest, “total catch” was calculated by modifying uʹ to include the total number of tagged fish reported for each release group, including those harvested and released. Calculations were otherwise performed as described above.

RESULTS


In 2015, 24,385 nonreward tagged hatchery catchables were released across 78 waters statewide (Table 1) and included 130 individual tag groups (Table 2). Anglers returned 2,321 of these tags within 365 days of each individual stocking event. Harvest and total catch varied widely (0-116.2%; some estimates surpass 100% due to correction factor [see methods above]) across all waters (Table 2). For all tags released in 2015 and reported within 365 days of release, average statewide harvest (± 90% C.I.) was 19.1% (± 1.9%), whereas average total catch for hatchery catchables was estimated as 26.3% (± 2.5%). The mean days-at-large for all tagged catchable trout was 74 days; the median value was 38 days. The average total length of catchable Rainbow Trout (standards and magnums) tagged in 2015 was 271 mm from all hatcheries.

In 2016, 21,198 nonreward tagged hatchery catchables were released across 77 waters

statewide (Table 3) and included 94 individual tag groups (Table 4). A total of 1,866 tags was returned by anglers within 365 days of each individual stocking event. Similar to 2015, harvest and total catch varied widely across all waters (Table 4). Average statewide harvest was 18.2% (± 2.0%) and average total catch was 24.6% (± 2.5%) for tags reported within 365 days of release. Mean days-at-large for all catchables tagged in 2016 was 80 days and the median value was 46 days. The average total length of catchables (standards and magnums) tagged in 2016 was 274 mm from all hatcheries.

The total number of tags returned by anglers diminished considerably during the second

year of evaluation. For release year 2015, 119 tags were returned within 366-730 days (Table 5); average statewide harvest was 3.5% (± 0.8%) and average total catch was 3.8% (± 0.8%). For release year 2016, 114 tags were returned within 366-730 days (Table 6). Average statewide harvest was 4.3% (± 2.0%) and average total catch was 5.5% (± 2.0%).

Magnum Rearing

Lakes and Reservoirs

In 2014, total length for magnums averaged 309 mm and standards averaged 262 mm at stocking. For the first year at-large, magnums had an average catch rate of 39.3% (± 6.6%) while their standard counterparts had a catch rate of 21.4% (± 4.8%; Figure 2). In 2015, total length for magnums averaged 311 mm and standards averaged 256 mm at stocking. Magnums were caught at 30.5% (± 10.3%) and standards at 12.2% (± 3.7%) during their first year at-large (Figure 2).

Anglers returned fewer tags during the second year at-large. Average total catch for

magnums released in 2014 and returned within 366-730 days was 3.7% (± 1.5%), whereas average catch for standards released in 2014 was 1.8% (± 0.6%; Figure 3). For fish released in

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2015 and returned within 366-730 days, average catch for magnums was 1.4% (± 1.5%) and average catch for standards was 1.1% (± 1.0%; Figure 3).

Flowing Waters

In 2015, magnums averaged 308 mm and standards averaged 252 mm at stocking. Average catch rate for magnums was 26.6% (± 5.6%), whereas standard catchables were caught at a rate of 16.6% (± 4.7%, Figure 2). In 2016, magnums averaged 303 mm, whereas standards averaged 255 mm at stocking. Average catch rate for magnums was 27.3% (± 6.8%) and standards were caught at a rate of 18.7% (± 8.2%, Figure 2). Only one tag was returned by an angler during the second year of this evaluation (Figure 3).

Baffled Raceway

Of the 29 water bodies evaluated, tagged fish were caught and reported from every system except Mores Creek (Figure 4). Fish reared in the baffled raceway at Nampa Fish Hatchery exhibited slightly higher average return-to-creel rates than fish reared in unbaffled raceways when released into lakes, reservoirs, and flowing waters (Table 7). Conversely, fish reared in the unbaffled control raceway exhibited a higher average catch rate when released into ponds.

Tag Reporting Rate

Fifty-dollar reward tags were released across 17 water bodies in 2015 and 16 waters in 2016. The statewide overall average tag reporting rate for catchables in 2015 was 45.1%, whereas average tag reporting rate in 2016 was 43.3%. The preliminary average tag reporting rate for 2017 is 50.9% (Figure 5).

DISCUSSION


Estimates of statewide harvest in 2015 (19.1%) and 2016 (18.2%) remain similar to estimates for fish released in 2011-2014 (Cassinelli 2014, 2015, 2016). Total catch estimates of hatchery catchable trout released in 2015 (26.3%) and 2016 (24.6%) remain comparable to the statewide estimates of previous years. Similarly, the mean and median days-at-large for fish stocked in 2015 and 2016 fish remain similar to those observed in previous years. A size-grading evaluation was conducted in 2015 and 2016, and results from that evaluation will be summarized in detail in a forthcoming report.

Magnum Rearing

Overall, magnum-sized catchable trout were reported by anglers at a higher rate than standard-sized catchables. This result was more pronounced for magnums stocked in lakes and reservoirs, where magnums had a 107% increase in returns when compared to their standard counterparts. Anglers also reported catch of magnums more frequently than standards in flowing waters, but the effect of magnum rearing on return-to-creel in flowing waters (53%) was only half of the value observed for lakes and reservoirs. These results confirm the added benefit of rearing catchables to an increased size. Despite having to reduce overall fish production by approximately 40% to accommodate the larger sized fish in the raceways, anglers benefit from magnum rearing

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by catching larger, more desirable fish. A comprehensive completion report summarizing the magnum rearing program will be included in a forthcoming annual project report (2019).

Baffled Raceway

No appreciable difference in catch rate was observed between fish reared in baffled and unbaffled raceways. Although fish reared in the baffled raceway showed marginally improved return rates when stocked into lakes, reservoirs, and flowing waters, these results are preliminary until all tags have been at liberty for a full 365-day period. Furthermore, this evaluation was repeated in 2018, and anglers are continuing to report tags from both release years. Results from both release years will be summarized and discussed in detail in forthcoming reports.

Tag Reporting Rate

Year-specific tag reporting rates have been variable over the past several years (Cassinelli 2015), indicating that annual tag reporting rates will likely continue to fluctuate based on waters receiving reward tags. However, tag reporting rates for 2015 and 2016 were similar, and the preliminary 2017 tag reporting rate suggests a comparable rate. It should be noted that tag reporting rates will fluctuate each year by chance alone, but no major annual fluctuations have been observed in year-specific estimates for seven consecutive years. Considering the minimal number of reward tags needed each year to calculate tag reporting rate annually, $50 reward tags should be released each year that the Tag-You’re-It program is used for broad-scale evaluations of catchable trout return-to-creel.

Despite minute annual fluctuations in tag reporting rate, inferences and management

actions made on annual harvest and catch estimates appear to be unaffected by annual reporting rate. Estimation of annual catch using both year-specific and aggregate (i.e., average rate across several years) reporting rates has demonstrated that annual variation in catch observed at some waters is likely real and not an artifact of annual variation in tag reporting rate (Cassinelli 2016). Furthermore, general linear models fit to year-specific and aggregate tag reporting rates yielded similar harvest and catch estimates, indicating that conclusions drawn regarding factors that influence catch of stocked fish were not affected by tag reporting rates (Cassinelli 2016).

As more reward tags are caught and reported by anglers over time, evaluating a new

approach for estimating reporting rate may be warranted. Using an aggregate tag reporting rate may prove more efficient if tag returns do not show a long-term increasing or decreasing trend. This approach would help minimize year-specific biases in tag returns related to chance variation. I will continue to monitor variation in year-specific reporting rates and trends in the aggregate reporting rate through time to determine if using the aggregate method becomes more appropriate than the current method of using year-specific rates.

FUTURE RESEARCH AND MANAGEMENT RECOMMENDATIONS

1. Continue collecting and compiling tag returns. a. Consider monitoring angler effort in association with catchable stocking to assess

how effort may influence return rates. Rather than intensive creel surveys, this could be done with car counters and trail cameras as a modified method of approximating relative angler effort across waters.

9

b. Consider the use of a hierarchical model to estimate harvest and catch rates, where all prior tag loss and reporting rate information is used to generate exploitation estimates for a particular release group.

2. Further evaluate hatchery rearing techniques and assess if experimental rearing conditions result in a significant increase in return-to-creel.

a. Despite needing to reduce overall fish production to grow catchables to magnum

size, the benefit of magnum production on return-to-creel is clear. Managers should consider requesting magnum catchables when supplementing lakes, reservoirs, or flowing waters with hatchery trout to maximize the benefit to anglers.

b. Measure current velocity in the baffled and unbaffled raceway at Nampa Fish Hatchery to quantify and characterize rearing conditions and determine the effect on return-to-creel.

c. Evaluate a reduced-fat feed formulation and determine if operational feed costs could be lowered while achieving comparable or improved return-to-creel rates.

3. Continue releasing $50 reward tags at low rates each year to assess whether reporting rates by anglers fluctuate through time or trend upward, downward, or stabilize.

10

ACKNOWLEDGEMENTS

I would like to acknowledge the hard work and dedication of Kyle Gatt, Jordan Everson, Patrick Kennedy, Kevin Meyer, Luciano Chiaramonte, Tony Lamansky, Kristi Stevenson, Dennis Daw, Kevin Nelson, and Steve Elle for assisting with tagging fish. I would also like to thank John Cassinelli and Regional Fisheries Managers for recommendations and help designing and implementing these studies. Additionally, I would like to thank Kevin Yelton and the staff at American Falls Fish Hatchery, Joe Chapman and the staff at Hagerman State Fish Hatchery, and Bob Becker and the staff at Nampa Fish Hatchery for all their assistance tagging, rearing, and releasing fish. I would also like to thank Tony Lamansky for the development and continued technical support of the Microsoft™ Access® database that stores all tagging events and returns. A big thank you goes to Liz Mamer and Kristi Stevenson for all their hard work managing the database and the constant tag return information. I also thank John Cassinelli, Jennifer Vincent, and Beau Gunter for editing this report. Funding for this work was provided by anglers and boaters through their purchase of Idaho fishing licenses, tags, and permits, and from federal excise taxes on fishing equipment and boat fuel through the Sport Fish Restoration Program.

11

LITERATURE CITED

Ashe, W., J. Seiders, and S. Davis. 2014. Fishery final report, series 14-1. Habitat variables influencing the return of hatchery-reared fall-yearling Brook Trout in Maine waters. Maine Department of Inland Fisheries and Wildlife.

Barnes, M. E., G. Simpson, and D. J. Durben. 2009. Post-stocking harvest of catchable-sized

Rainbow Trout enhanced by dietary supplementation with a fully fermented commercial yeast culture during hatchery rearing. North American Journal of Fisheries Management 29:1287-1295.

Boersen, G., and H. Westers. 1986. Waste solids control in hatchery raceways. The Progressive

Fish Culturist 48:151-154. Cassinelli, J., and M. Koenig. 2013. Idaho Department of Fish and Game. Annual Performance

Report Number 13-04. Boise. Cassinelli, J. 2014. Idaho Department of Fish and Game. Annual Performance Report Number

14-02. Boise. Cassinelli, J. 2015. Idaho Department of Fish and Game. Annual Performance Report Number

15-07. Boise. Cassinelli, J. 2016. Idaho Department of Fish and Game. Annual Performance Report Number

16-09. Boise. Cassinelli, J. D., and K. A. Meyer. 2018. Factors influencing return-to-creel of hatchery catchable-

sized Rainbow Trout stocked in Idaho lentic waters. Fisheries Research 204:316-323. Cassinelli, J. D., K. A. Meyer, and M. K. Koenig. 2016. Effects of rearing density on return-to-creel

of hatchery catchable Rainbow Trout stocked in Idaho lentic waters. North American Journal of Aquaculture. In Press.

Guy, C. S., H. L. Blankenship, and L. A. Nielsen. 1996. Tagging and marking. Pages 353–383 in

B. R. Murphy and D. W. Willis, editors. Fisheries techniques. American Fisheries Society, Bethesda, Maryland.

Kindschi, G. A., R. G. Thompson, and A. P. Mendoza. 1991. Use of raceway baffles in Rainbow

Trout culture. The Progressive Fish Culturist 53:97-101. Koenig, M. K., and K. A. Meyer. 2011. Relative performance of diploid and triploid catchable

rainbow trout stocked in Idaho lakes and reservoirs. North American Journal of Fisheries Management 31:605-613.

Meyer, K. A., F. S. Elle, T. Lamansky, E. R. J. M. Mamer, and A. E. Butts. 2012. A reward-recovery

study to estimate tagged-fish reporting rates by Idaho anglers. North American Journal of Fisheries Management 32:696-703.

Meyer, K. A., and D. J. Schill. 2014. Use of a statewide angler tag reporting system to estimate

rates of exploitation and total mortality for Idaho sport fisheries. North American Journal of Fisheries Management 34:1145-1158.

12

Mullan, J. W. 1956. The comparative returns of various sizes of trout stocked in Massachusetts

streams. The Progressive Fish-Culturist 18(1):35-38. Pollock, K. H., J. M. Hoenig, W. S. Hearn, and B. Calingaert. 2001. Tag reporting rate estimation:

1. An evaluation of the high-reward tagging method. North American Journal of Fisheries Management 21:521-532.

Quinn, S. P. 1996. Trends in regulatory and voluntary catch-and-release fishing. Pages 152-162

in L. E. Miranda, and D. R. DeVries, editors. Multidimensional approaches to reservoir fisheries management. American Fisheries Society, Symposium 16, Bethesda, Maryland.

Trushenski, J. T., T. Flagg, and C. C. Kohler. 2010. Use of hatchery fish for conservation,

restoration, and enhancement of fisheries. Pages 261–293 in W. Hubert and M. Quist, editors. Inland fisheries management in North America, 3rd edition. American Fisheries Society, Bethesda, Maryland.

Wiley, R. W., R. A. Whaley, J. B. Satake, and M. Fowden. 1993. Assessment of stocking hatchery

trout: a Wyoming perspective. North American Journal of Fisheries Management 13(1):160-170.

Yates, F. 1953. Sampling methods for censuses and surveys, Second Edition. Charles Griffin and

Co. Ltd., London. Yule, D. L., R. A. Whaley, P. H. Mavrakis, D. D. Miller, and S. A. Flickinger. 2000. Use of strain,

season of stocking, and size at stocking to improve fisheries for Rainbow Trout in reservoirs with walleyes. North American Journal of Fisheries Management 20:10-18.

13

Table 1. Waters that were stocked with tagged catchables in 2015 along with the total number of catchables stocked in those waters for the calendar year.

Water Body

Total catchables stocked in

2015

Total number of stockings in

2015

Total number of tagged fish

stocked

Alturas Lake 5,185 3 149American Falls Reservoir 109,291 4 790Arrowrock Reservoir 13,388 2 798Ashton Reservoir 38,750 4 1,399Avondale Lake 2,000 1 149Bear River 13,647 14 149Blackfoot Reservoir 40,423 4 799Blair Trail Reservoir 6,148 6 340Blue Creek Reservoir 2,100 2 100Blue Mountain Pond 898 3 90Bull Trout Lake 3,292 4 400Campbell 's Pond 8,162 9 104Cape Horn Lake #1 917 3 60Crooked River 3,514 4 400Crystal Springs Pond 6,760 15 99Deep Creek Reservoir 8,026 2 300Dog Creek Reservoir 6,706 4 300Eagle Island Park Pond 1,914 4 50Feathervil le Dredge Pond 5,523 6 398Foster Reservoir 5,854 3 300Frank Oster Lake #1 14,510 27 159Frank Oster Lake #4 2,033 6 48Freeman Lake 4,516 4 138Glendale Reservoir 7,952 2 300Gold Fork River 2,150 3 100Grimes Creek 6,027 6 398Hayden Lake 45,387 6 200Indian Creek 525 2 98Johnson Reservoir 1,750 1 300Lake Cleveland 5,531 4 199Little Bayhorse Lake 4,050 8 200Lost Valley Reservoir 8,958 2 399Manns Creek Reservoir 5,797 3 400Middle Fork Boise River 5,839 4 400Middle Fork Payette River 9,970 13 560Mores Creek 5,931 7 399Mosquito Flat Reservoir 5,653 4 549North Fork Boise River 10,037 6 400North Fork Payette River 4,710 5 150Oakley Reservoir 26,215 3 597Payette River 1,007 2 49Rock Creek 3,274 2 100Ryder Park Pond 7,000 9 98Sage Hen Reservoir 7,197 3 250Salmon Falls Creek Reservoir 147,253 8 1,293Silver Creek 9,976 13 558Snake River 13,250 20 398Spring Valley Reservoir 28,057 5 589Squaw Creek Pond 663 3 40Stanley Lake 8,440 4 200Sublett Reservoir 4,961 2 298Treasureton Reservoir 16,789 4 300Warm Lake 14,414 2 400Wilson Creek 3,421 13 100Totals 725,741 303 17,841

14

Table 2. Total nonreward tags released by water body, hatchery, stocking date, and treatment in 2015. Harvest and Catch were estimated through the first year at large with associated 90% confidence intervals (C.I.).

Harvested Harvested b/c tagged

Released Estimate 90% C.I. Estimate 90% CI

Avondale Lake Sandpoint 21-Sep-15 None 149 4 0 3 6.0% 5.0% 10.5% 6.6%Crystal Lake Hagerman 27-Apr-15 None 50 1 0 0 4.5% 7.3% 4.5% 7.3%

Freeman Lake Sandpoint 21-Sep-15 None 138 1 0 0 1.6% 2.7% 1.6% 2.7%Hayden Lake Sandpoint 15-Apr-15 None 200 4 0 1 4.5% 3.7% 5.6% 4.2%

Campbell's Pond Clearwater 06-May-15 None 104 14 2 3 30.1% 13.2% 40.8% 15.4%Palouse River Dredge Pond Clearwater 06-May-15 None 50 7 1 2 31.3% 18.7% 44.7% 22.0%

Grading Ctrl 49 4 1 2 18.2% 14.7% 31.9% 19.1%Grading Tx Early Laggers 50 4 0 0 17.9% 14.4% 17.9% 14.4%Grading Tx Early Leaders 50 2 0 0 8.9% 10.3% 8.9% 10.3%

Grading Tx Early Leaders NB 50 2 0 0 8.9% 10.3% 8.9% 10.3%Grading Ctrl 197 27 1 1 30.6% 10.3% 32.9% 10.7%

Grading Tx Early Leaders 193 26 3 1 30.1% 10.3% 34.7% 11.1%Grading Tx Late Leaders 199 30 3 2 33.7% 10.8% 39.3% 11.8%

Standards 246 13 3 2 11.8% 5.6% 16.3% 6.6%Magnums 250 33 0 9 29.5% 9.2% 37.5% 10.6%



Grading Tx Early Laggers 200 15 0 1 16.8% 7.4% 17.9% 7.6%Grading Tx Early Leaders 199 18 1 1 20.2% 8.2% 22.5% 8.6%

Grading Tx Early Leaders NB 199 26 0 0 29.2% 10.0% 29.2% 10.0%15-Jun-15 Magnums 90 6 2 0 14.9% 10.0% 19.9% 11.5%06-Jul-15 Orange Floy Tag 100 23 0 4 51.4% 17.5% 60.3% 19.0%

Standards 75 2 0 0 6.0% 6.9% 6.0% 6.9%Magnums 75 1 0 0 3.0% 4.9% 3.0% 4.9%

03-Sep-15 Magnums 60 2 0 0 7.4% 8.6% 7.4% 8.6%Magnums 50 3 0 1 13.4% 12.5% 17.9% 14.4%Standards 50 3 1 0 13.4% 12.5% 17.9% 14.4%

15-Jun-15 None 100 4 0 0 8.9% 7.3% 8.9% 7.3%06-Jul-15 Orange Floy Tag 100 0 1 0 0.0% 0.0% 2.2% 3.7%

17-Aug-15 Orange Floy Tag 100 0 1 0 0.0% 0.0% 2.2% 3.7%Eagle Island Pond Nampa 16-Dec-15 None 50 5 0 2 22.3% 16.0% 31.3% 18.7%

Magnums 44 6 0 1 30.5% 19.6% 35.5% 21.1%Standards 45 3 1 0 14.9% 13.9% 19.9% 15.9%Magnums 50 7 0 0 31.3% 18.7% 31.3% 18.7%Standards 50 1 0 0 4.5% 7.3% 4.5% 7.3%

08-Jul-15 Exploitation 99 0 0 1 0.0% 0.0% 2.3% 3.7%20-Jul-15 Orange Floy Tag 100 0 0 0 0.0% 0.0% 0.0% 0.0%

Magnums 50 4 0 2 17.9% 14.4% 26.8% 17.4%Standards 50 3 0 2 13.4% 12.5% 22.3% 16.0%Magnums 24 1 0 0 9.3% 15.1% 9.3% 15.1%Standards 25 1 0 2 8.9% 14.5% 26.8% 24.3%Magnums 270 62 6 10 51.3% 12.5% 64.5% 14.5%Standards 270 18 4 7 14.9% 6.1% 24.0% 7.9%Magnums 150 24 1 5 35.7% 12.4% 44.7% 14.0%Standards 150 2 0 3 3.0% 3.5% 7.4% 5.5%Magnums 50 7 0 0 31.3% 18.7% 31.3% 18.7%Standards 50 9 0 1 40.2% 21.0% 44.7% 22.0%Magnums 100 13 0 4 29.0% 13.2% 38.0% 15.1%Standards 100 2 0 4 4.5% 5.2% 13.4% 9.0%Magnums 100 1 0 1 2.2% 3.7% 4.5% 5.2%Standards 100 1 1 0 2.2% 3.7% 4.5% 5.2%Magnums 45 11 1 2 54.6% 25.1% 69.5% 27.7%Standards 45 2 0 1 9.9% 11.4% 14.9% 13.9%

02-Jun-15 None 86 7 0 0 18.2% 11.2% 18.2% 11.2%15-Jun-15 None 75 4 0 0 11.9% 9.7% 11.9% 9.7%06-Jul-15 Orange Floy Tag 75 2 0 1 6.0% 6.9% 8.9% 8.4%20-Jul-15 Orange Floy Tag 75 1 0 1 3.0% 4.9% 6.0% 6.9%

17-Aug-15 Orange Floy Tag 74 1 0 1 3.0% 5.0% 6.0% 7.0%25-Aug-15 None 75 1 0 0 3.0% 4.9% 3.0% 4.9%

3B

Snake River American Falls 21-Apr-15

20-Apr-15

Treatment Tags Released

Disposition Adjusted HarvestRegion Water Body Hatchery Tagging Date

1

26-Oct-15

18-May-15

Arrowrock Reservoir Hagerman

24-Sep-15

Winchester Lake Hagerman 26-Oct-15

17-Aug-15NampaBull Trout Lake

Crooked River Nampa

Grimes Creek Nampa

Lucky Peak Reservoir Nampa 07-Apr-15

Mann Creek Reservoir Nampa18-May-15

24-Sep-15

Middle Fork Boise River Nampa25-Jun-15

13-Aug-15

18-May-15

Adjusted Total Catch

Spring Valley Reservoir Hagerman

18-May-15

09-Jun-15

Indian Creek Nampa07-May-15

25-Sep-15

2

Middle Fork Payette River Nampa

15

Table 2. Continued.




08-Jul-15 Exploitation 100 1 0 0 2.2% 3.7% 2.2% 3.7%20-Jul-15 Orange Floy Tag 100 1 0 0 2.2% 3.7% 2.2% 3.7%


18-Mar-15 Normal Production 50 0 1 1 0.0% 0.0% 8.9% 10.3%16-Apr-15 Normal Production 50 1 0 0 4.5% 7.3% 4.5% 7.3%08-Oct-15 Normal Production 49 2 0 0 9.1% 10.5% 9.1% 10.5%


02-Jun-15 None 76 9 0 2 26.5% 14.3% 32.3% 15.7%15-Jun-15 None 75 2 1 1 6.0% 6.9% 11.9% 9.7%06-Jul-15 Orange Floy Tag 75 7 0 0 20.9% 12.8% 20.9% 12.8%20-Jul-15 Orange Floy Tag 75 1 0 0 3.0% 4.9% 3.0% 4.9%

Magnums 37 0 0 1 0.0% 0.0% 6.0% 9.8%Standards 46 1 0 1 4.9% 7.9% 9.7% 11.2%

25-Aug-15 None 75 1 1 3 3.0% 4.9% 14.9% 10.9%Magnums 25 3 2 0 26.8% 24.3% 44.7% 30.3%Standards 25 4 1 1 35.7% 27.6% 53.6% 32.6%Magnums 25 1 0 1 8.9% 14.5% 17.9% 20.2%Standards 25 3 2 0 26.8% 24.3% 44.7% 30.3%Magnums 25 9 0 0 80.4% 37.6% 80.4% 37.6%Standards 25 5 0 0 44.7% 30.3% 44.7% 30.3%Magnums 50 4 2 0 17.9% 14.4% 26.8% 17.4%Standards 50 0 0 1 0.0% 0.0% 4.5% 7.3%Magnums 170 37 1 0 48.6% 14.0% 49.9% 14.2%Standards 169 8 1 0 10.6% 6.2% 11.9% 6.6%Magnums 67 3 0 1 10.0% 9.4% 13.3% 10.9%Standards 67 2 0 0 6.7% 7.7% 6.7% 7.7%Magnums 200 23 3 5 25.7% 9.3% 34.6% 10.9%Standards 200 13 1 0 14.5% 6.8% 15.6% 7.1%Magnums 35 0 0 0 0.0% 0.0% 0.0% 0.0%Standards 35 0 0 0 0.0% 0.0% 0.0% 0.0%

05-May-15 None 200 5 0 2 5.6% 4.2% 7.8% 4.9%Grading Ctrl 35 0 0 0 0.0% 0.0% 0.0% 0.0%

Grading Tx Early Laggers 35 0 0 0 0.0% 0.0% 0.0% 0.0%Grading Tx Early Leaders 35 0 0 0 0.0% 0.0% 0.0% 0.0%Grading Tx Late Leaders 35 0 0 0 0.0% 0.0% 0.0% 0.0%

09-Jun-15 None 77 14 1 2 40.6% 17.4% 49.3% 19.1%28-Sep-15 None 75 0 0 2 0.0% 0.0% 6.0% 6.9%

Crystal Lake American Falls 08-Jun-15 None 40 2 0 1 11.2% 12.8% 16.8% 15.5%Grading Ctrl 90 10 0 3 24.8% 12.8% 32.3% 14.6%





Grading Tx Early Laggers 40 8 0 2 44.7% 24.3% 55.9% 26.7%Grading Tx Early Leaders 40 9 1 1 50.3% 25.6% 61.4% 27.8%Grading Tx Late Leaders 40 12 1 0 67.0% 28.7% 72.6% 29.6%

Grading Ctrl 35 12 0 1 76.6% 32.0% 83.0% 32.9%Grading Tx Early Laggers 34 9 0 1 59.1% 29.4% 65.7% 30.6%Grading Tx Early Leaders 35 4 1 1 25.5% 20.2% 38.3% 24.2%Grading Tx Late Leaders 34 6 3 2 39.4% 24.9% 72.3% 31.7%


Grading Tx Early Leaders NB 25 7 0 1 62.6% 34.5% 71.5% 36.2%

3B

3M

4

Castle Rock Pond American Falls

Dierke's Lake Hagerman 21-Sep-15

Dog Creek Reservoir Hagerman 26-Oct-15

Featherville Dredge Pond

Water Body Hatchery Tagging Date Treatment Tags ReleasedDisposition Adjusted Harvest Adjusted Total Catch

Region

Hagerman

19-May-15

15-Jun-15

18-Aug-15

Warm Lake Nampa 25-Jun-15

Weiser River Nampa 17-Jun-15

Blair Trail Reservoir Hagerman 19-May-15

Gold Fork Creek Nampa 17-Jun-15

Lost Valley Reservoir Nampa 09-Jun-15

North Fork Payette River

Nampa 25-Jun-15

Sage Hen Reservoir Nampa 18-May-15

Silver Creek Nampa

18-May-15

13-Aug-15

Wilson Creek Nampa

07-May-15

13-Aug-15

17-Sep-15

Mores Creek Nampa

18-May-15

09-Jun-15

North Fork Boise River Nampa25-Jun-15

13-Aug-15

Payette River Nampa

16

Table 2. Continued.



19-May-15 Exploitation 35 13 1 1 83.0% 32.9% 95.8% 34.4%15-Jun-15 Exploitation 32 4 0 1 27.9% 22.0% 34.9% 24.3%29-Sep-15 Exploitation 35 6 1 2 38.3% 24.2% 57.5% 28.7%26-Oct-15 Exploitation 35 4 0 3 25.5% 20.2% 44.7% 25.9%




Grading Tx Early Leaders NB 50 17 1 5 76.0% 27.5% 102.8% 30.8%Lake Walcott Hagerman 26-Feb-15 None 299 12 2 3 9.0% 4.4% 12.7% 5.3%


Grading Ctrl 180 18 2 0 22.3% 9.0% 24.8% 9.5%Grading Tx Early Leaders 175 21 1 1 26.8% 10.0% 29.4% 10.5%Grading Tx Late Leaders 178 33 2 1 41.4% 12.6% 45.2% 13.3%

26-Feb-15 None 198 47 2 8 53.0% 14.0% 64.3% 15.7%Grading Ctrl 25 5 0 2 44.7% 30.3% 62.6% 34.5%

Grading Tx Early Leaders 25 4 0 3 35.7% 27.6% 62.6% 34.5%Grading Tx Late Leaders 25 4 1 1 35.7% 27.6% 53.6% 32.6%




Grading Tx Early Leaders NB 25 2 0 2 17.9% 35.7%Grading Ctrl 296 8 0 2 6.0% 3.6% 7.5% 4.0%




Grading Tx Early Leaders NB 73 9 1 5 27.5% 14.8% 45.9% 18.9%21-Oct-15 None 457 25 2 13 12.2% 4.4% 19.6% 5.8%


Grading Tx Early Leaders NB 200 1 0 2 1.1% 1.8% 3.4% 3.2%Magnums 75 3 0 7 8.9% 8.4% 29.8% 15.2%Standards 75 2 0 6 6.0% 6.9% 23.8% 13.7%


Grading Tx Early Leaders NB 25 0 0 0 0.0% 0.0% 0.0% 0.0%Deep Creek Reservoir Nampa 21-May-15 Cormorant 300 14 1 13 10.4% 4.8% 20.9% 7.0%


Grading Tx Early Leaders NB 15 1 1 3 14.9% 23.8% 74.5% 46.3%Foster's Reservoir Grace 18-May-15 Cormorant 300 14 0 1 10.4% 4.8% 11.2% 5.0%Glendale Reservoir Grace 18-May-15 Cormorant 300 9 5 11 6.7% 3.8% 18.6% 6.6%


Grading Tx Early Leaders NB 125 5 0 0 8.9% 6.6% 8.9% 6.6%

4

5

Jensen Grove Pond American Falls

Hagerman

19-May-15

21-Sep-15

18-Aug-15

15-Jun-15

20-Apr-15

Hagerman 15-Jun-15

18-Aug-15

21-Sep-15

Hagerman20-Apr-15

24-Sep-15

20-May-15

American Falls27-Oct-15

21-Sep-15

18-Aug-15

18-Aug-15

21-Apr-15

Bear River Grace

Crystal Spring pond American Falls

Edson Fichter Pond American Falls

Salmon Falls Creek Reservoir

Sublett Reservoir American Falls

American Falls Reservoir

Riley Creek Pond

Rock Creek Hagerman

Rupert Gravel Pond Hagerman

Region Water Body Hatchery Tagging Date Treatment Tags Released

Disposition Adjusted Harvest Adjusted Total Catch

Filer / LQ Drain Pond

Frank Oster Lake #1 Hagerman

Frank Oster Lake #4 Hagerman

Lake Cleveland Hagerman

Little Smokey Creek Hagerman

Oakley Reservoir Hagerman

17

Table 2. Continued.



Johnson Reservoir Grace 18-May-15 Cormorant 300 9 3 9 6.7% 3.8% 15.6% 6.0%Lamont Res Grace 18-May-15 Cormorant 300 1 0 1 0.7% 1.2% 1.5% 1.7%





Grading Tx Early Leaders NB 50 3 0 0 13.4% 12.5% 13.4% 12.5%Magnums 50 4 1 0 17.9% 14.4% 22.3% 16.0%

Treasureton Reservoir Grace 18-May-15 Cormorant 300 0 0 2 0.0% 0.0% 1.5% 1.7%Grading Ctrl 25 4 0 5 35.7% 27.6% 80.4% 37.6%



















08-May-15 None 30 5 0 0 37.2% 25.7% 37.2% 25.7%12-Jun-15 None 30 11 0 0 81.9% 34.9% 81.9% 34.9%11-Jun-15 None 30 0 0 0 0.0% 0.0% 0.0% 0.0%09-Jul-15 Exploitation 30 1 0 0 7.4% 12.1% 7.4% 12.1%22-Jun-15 None 50 4 1 1 17.9% 14.4% 26.8% 17.4%01-Jul-15 Exploitation 50 3 0 0 13.4% 12.5% 13.4% 12.5%19-Jul-15 None 50 1 0 1 4.5% 7.3% 8.9% 10.3%

29-May-15 None 150 2 0 0 3.0% 3.5% 3.0% 3.5%24-Jun-15 Exploitation 150 4 0 0 6.0% 4.9% 6.0% 4.9%15-Jul-15 Exploitation 149 4 0 0 6.0% 5.0% 6.0% 5.0%

12-Aug-15 None 100 0 0 1 0.0% 0.0% 2.2% 3.7%Nampa 19-May-15 Normal Production 20 0 0 0 0.0% 0.0% 0.0% 0.0%

Sawtooth 15-Jun-15 Exploitation 20 0 0 0 0.0% 0.0% 0.0% 0.0%Magnums 100 4 0 0 8.9% 7.3% 8.9% 7.3%Standards 100 4 1 0 8.9% 7.3% 11.2% 8.2%

17-Aug-15

5

6

7

Cape Horn Lake #1 Sawtooth

Little Bayhorse Lake Sawtooth

Mosquito Flat Reservoir Mackay

Squaw Creek Pond

Stanley Lake Nampa

Snake River Gem State American Falls

16-Jun-15

22-Sep-15

Snake River Henry's Fork American Falls 18-Aug-15

Blue Mountain Pond Mackay

Blue Creek Reservoir American Falls

20-May-15

22-Sep-15

Island Park Reservoir Nampa 25-Jun-15

Ryder Park Pond American Falls 21-Apr-15

Snake River (upper) R5 American Falls 22-Sep-15

Wellness Reservoir American Falls 27-Oct-15

Ashton Reservoir American Falls

20-May-15

16-Jun-15

Portneuf River (Upper) Grace 01-Oct-15

Rock Creek East Fork American Falls 18-Aug-15

Snake River (Below American Falls) American Falls 16-Jun-15

Region Water Body Hatchery Tagging Date Treatment Tags Released


18

Table 3. Waters that were stocked with tagged catchables in 2016 along with the total number of catchables stocked in those waters for the calendar year.

Water Body

Total catchables stocked in

2016

Total number of stockings in

2016

Total number of tagged fish

stocked

Arrowrock Reservoir 12,627 1 797Ashton Reservoir 38,773 4 800Avondale Lake 2,000 1 193Blair Trail Reservoir 3,720 3 244Blue Creek Reservoir 2,000 1 199Boise River 30,836 23 3Cape Horn Lake #1 1,800 6 60Cascade Reservoir 93,755 7 1,189Chesterfield Reservoir 32,664 3 400Crooked River 1,949 2 199Dog Creek Reservoir 6,860 2 299Eagle Island Park Pond 3,626 8 50Edson Fichter Pond 6,375 8 121Emerald Lake 2,343 3 100Feathervil le Dredge Pond 4,952 4 258Fernan Lake 10,644 7 447Foster Reservoir 3,555 3 200Frank Oster Lake #1 14,237 31 240Freeman Lake 2,177 3 225Glendale Reservoir 6,162 3 400Gold Fork River 2,287 3 65Grimes Creek 3,027 3 286Hayden Lake 14,835 4 430Indian Creek 2,588 10 100Island Park Reservoir 155,081 4 793Lake Cleveland 5,170 2 201Lake Walcott 24,270 4 93Little Bayhorse Lake 3,344 3 74Lower Twin Lake 5,928 5 597Lucky Peak Reservoir 16,210 3 399Magic Reservoir 5,619 2 399Middle Fork Boise River 6,196 3 396Middle Fork Payette River 10,390 13 582Mirror Lake 3,239 3 200Moose Creek Reservoir 12,229 5 299Mores Creek 3,005 3 300Mormon Reservoir 3,496 2 200North Fork Boise River 5,804 3 200North Fork Payette River 5,729 9 100Oakley Reservoir 15,442 3 500Payette Greenbelt Pond 3,206 7 49Perkins Lake 1,218 3 49Rose Pond 2,600 4 99Ryder Park Pond 7,000 10 200Salmon Falls Creek Reservoir 53,508 7 1,096Silver Creek 10,240 13 649Spicer Pond 2,200 2 99Spring Valley Reservoir 22,863 5 898Squaw Creek Pond 1,032 4 52Steamboat Pond 3,600 7 150Treasureton Reservoir 130 1 200Valley Creek 3,250 7 225Weiser Community Pond 3,433 7 49Wilson Creek 5,623 23 50Winchester Lake 25,114 5 999Totals 729,961 315 17,502

19

Table 4. Total nonreward tags released by water body, hatchery, stocking date, and treatment in 2016. Harvest and Catch were estimated through the first year at large with associated 90% confidence intervals (C.I.).

HarvestedHarvested b/c tagged Released Estimate 90% C.I. Estimate 90% CI

Avondale Lake Sandpoint 20-Sep-16 None 193 13 1 1 15.7% 7.4% 18.1% 8.0%12-Apr-16 None 150 15 1 0 23.3% 10.2% 24.8% 10.5%02-May-16 None 150 9 0 2 14.0% 7.8% 17.1% 8.7%21-Jun-16 None 147 7 1 0 11.1% 7.0% 12.7% 7.5%12-Apr-16 None 149 4 0 0 6.3% 5.2% 6.3% 5.2%18-May-16 None 149 4 1 1 6.3% 5.2% 9.4% 6.4%21-Jun-16 None 132 1 0 2 1.8% 2.9% 5.3% 5.1%12-Apr-16 None 149 13 0 1 20.3% 9.5% 21.9% 9.9%17-May-16 None 151 12 1 3 18.5% 9.0% 24.7% 10.5%01-Jun-16 None 147 18 0 1 28.5% 11.4% 30.1% 11.8%21-Sep-16 None 150 8 1 0 12.4% 7.3% 14.0% 7.8%02-May-16 None 100 15 0 1 34.9% 14.9% 37.3% 15.4%01-Jun-16 None 100 26 0 0 60.5% 19.7% 60.5% 19.7%25-Apr-16 None 49 6 0 1 28.5% 18.6% 33.3% 20.0%17-May-16 None 50 6 0 0 27.9% 18.2% 27.9% 18.2%23-May-16 None 50 3 0 0 14.0% 13.1% 14.0% 13.1%08-Jun-16 None 50 1 1 0 4.7% 7.6% 9.3% 10.7%12-Jul-16 None 50 1 0 0 4.7% 7.6% 4.7% 7.6%








Grading Tx Early Leaders NB 125 0 1 0 0.0% 1.9% 3.1%28-Mar-16 Magnums 96 13 1 4 31.5% 14.4% 43.7% 17.0%19-Apr-16 Magnums 100 12 0 1 27.9% 13.3% 30.3% 13.9%24-May-16 Normal Production 100 1 0 0 2.3% 3.8% 2.3% 3.8%01-Jul-16 Normal Production 100 4 0 0 9.3% 7.7% 9.3% 7.7%

Eagle Island Park Pond Nampa 17-Feb-16 Normal Production 50 8 1 10 37.3% 20.9% 88.5% 30.3%Magnums 49 3 0 4 14.3% 13.3% 33.3% 20.0%Standards 50 2 0 1 9.3% 10.7% 14.0% 13.1%Magnums 49 4 1 5 19.0% 15.3% 47.5% 23.5%Standards 38 1 1 4 6.1% 10.0% 36.8% 23.5%

06-Jul-16 Normal Production 100 4 1 1 9.3% 7.7% 14.0% 9.4%Magnums 25 2 1 0 18.6% 21.0% 27.9% 25.4%Standards 25 0 0 1 0.0% 9.3% 15.1%

19-Apr-16 Magnums 199 12 2 4 14.0% 6.9% 21.1% 8.6%24-May-16 Magnums 200 14 0 6 16.3% 7.5% 23.3% 9.1%

Magnums 99 6 1 10 14.1% 9.5% 40.0% 16.1%Standards 100 0 0 0 0.0% 0.0%Magnums 50 6 0 1 27.9% 18.2% 32.6% 19.6%Standards 50 3 0 1 14.0% 13.1% 18.6% 15.0%Magnums 40 5 0 0 29.1% 20.6% 29.1% 20.6%Standards 40 0 0 0 0.0% 0.0%

05-Jul-16 Normal Production 80 12 0 0 34.9% 16.4% 34.9% 16.4%20-Jul-16 None 80 3 0 0 8.7% 8.3% 8.7% 8.3%

15-Aug-16 Magnums 82 4 0 4 11.4% 9.3% 22.7% 13.1%

Region Water Body Hatchery Tagging Date Treatment Tags

Released

Sandpoint

Hayden Lake Sandpoint

Lower Twin Lake Sandpoint

Disposition Adjusted Exploitation Adjusted Total Use

Middle Fork Boise River Nampa 06-Aug-16

Middle Fork Payette River Nampa25-May-16

03-Aug-16

3B

Middle Fork Payette River Nampa

20-May-16

15-Jun-16

Indian Creek Nampa 19-May-16

Lucky Peak Reservoir Nampa

Crane Falls Reservoir Nampa

Crooked River Nampa

Grimes Creek Nampa

Spring Valley Reservoir

1

2

Hagerman

20-Jun-16

24-Oct-16

Winchester Lake Hagerman

20-Jun-16

24-Oct-16

Mirror Lake Sandpoint

Spicer Pond Sandpoint

Steamboat Pond Sandpoint

Fernan Lake

20

Table 4. Continued.



06-Jul-16 Normal Production 100 1 0 2 2.3% 3.8% 7.0% 6.6%Magnums 100 12 0 2 27.9% 13.3% 32.6% 14.4%Standards 100 4 1 1 9.3% 7.7% 14.0% 9.4%

Payette Greenbelt Pond Nampa 24-Feb-16 Normal Production 49 3 1 0 14.3% 13.3% 19.0% 15.3%Magnums 50 7 0 4 32.6% 19.6% 51.2% 24.1%Standards 50 2 2 1 9.3% 10.7% 23.3% 16.7%Magnums 40 4 0 1 23.3% 18.6% 29.1% 20.6%Standards 40 2 0 0 11.6% 13.3% 11.6% 13.3%Magnums 40 2 0 3 11.6% 13.3% 29.1% 20.6%Standards 40 3 0 3 17.5% 16.2% 34.9% 22.4%

05-Jul-16 Normal Production 80 3 0 1 8.7% 8.3% 11.6% 9.5%20-Jul-16 None 80 1 1 4 2.9% 4.8% 17.5% 11.7%

Magnums 40 1 0 1 5.8% 9.5% 11.6% 13.3%Normal Production 39 0 0 0 0.0% 0.0%

Weiser Community Pond Nampa 24-Feb-16 Normal Production 49 16 0 3 76.0% 28.8% 90.3% 30.8%Grading Ctrl 300 5 0 1 3.9% 2.9% 4.7% 3.2%


Grading Tx Early Leaders NB 298 6 0 0 4.7% 3.2% 4.7% 3.2%Magnums 30 2 0 0 15.5% 17.6% 15.5% 17.6%Standards 35 0 0 0 0.0% 0.0%Magnums 50 1 0 0 4.7% 7.6% 4.7% 7.6%Standards 50 5 1 0 23.3% 16.7% 27.9% 18.2%

Camas Pond 3 Hayspur 02-Jun-16 None 4 1 0 0 58.2% 83.5% 58.2% 83.5%20-Jun-16 None 75 13 1 1 40.4% 18.1% 46.6% 19.4%28-Sep-16 None 75 14 0 0 43.5% 18.8% 43.5% 18.8%






Grading Tx Early Laggers 15 0 0 0 0.0% 0.0%Grading Tx Early Leaders 15 3 0 0 46.6% 40.4% 46.6% 40.4%





Grading Tx Early Leaders NB 51 8 1 4 36.5% 20.5% 59.4% 25.5%21-Sep-16 None 199 5 0 0 5.9% 4.4% 5.9% 4.4%12-Oct-16 None 93 3 0 1 7.5% 7.1% 10.0% 8.2%





Tagging Date Treatment Tags

Released

Disposition Adjusted Exploitation Adjusted Total UseRegion Water Body Hatchery

Mores Creek Nampa 15-Jun-16

North Fork Boise River Nampa 27-Jun-16

Silver Creek Nampa

25-May-16

14-Jun-16

27-Jun-16

15-Aug-16

Cascade Reservoir Hagerman 26-May-16

16-May-16

Featherville Dredge Pond Hagerman

24-May-16

29-Aug-16

Gold Fork River Nampa 03-Aug-16

North Fork Payette River Nampa 22-Jun-16

Oakley Reservoir Hagerman 25-Apr-16

Snake River Lower American Falls 31-Aug-16

Lake Cleveland Hagerman 29-Aug-16

Lake Walcott Hagerman National

Magic Reservoir Hagerman 25-Apr-16

Filer / LQ Drain Pond Hagerman 19-Sep-16

Frank Oster Lake #1 Hagerman 19-Sep-164

3M

3B

Castle Rock Pond American Falls

Emerald Lake Nampa

21

Table 4. Continued.


Magnums 200 11 0 5 12.8% 6.6% 18.6% 8.0%Standards 200 3 1 1 3.5% 3.3% 5.8% 4.3%Magnums 200 8 3 2 9.3% 5.5% 15.1% 7.2%Standards 200 17 2 6 19.8% 8.3% 29.1% 10.2%Magnums 100 11 0 0 25.6% 12.8% 25.6% 12.8%Standards 100 6 1 0 14.0% 9.4% 16.3% 10.2%Magnums 200 16 0 4 18.6% 8.0% 23.3% 9.1%Standards 200 8 0 0 9.3% 5.5% 9.3% 5.5%Magnums 75 3 0 1 9.3% 8.8% 12.4% 10.2%Standards 75 3 4 3 9.3% 8.8% 31.0% 15.9%



Hatchery Hagerman 02-Nov-16 None 299 12 2 7 9.3% 4.6% 16.4% 6.3%Magnums 100 0 0 3 0.0% 7.0% 6.6%Standards 100 0 0 3 0.0% 7.0% 6.6%


Grading Tx Early Leaders NB 25 3 0 3 27.9% 25.4% 55.9% 34.1%Grading Ctrl 49 0 0 0 0.0% 0.0%

Grading Tx Early Laggers 50 0 0 0 0.0% 0.0%Grading Tx Early Leaders 50 0 1 0 0.0% 4.7% 7.6%


Grading Tx Early Laggers 47 0 0 0 0.0% 0.0%Grading Tx Early Leaders 45 4 0 0 20.7% 16.6% 20.7% 16.6%


Grading Tx Early Laggers 198 1 0 1 1.2% 1.9% 2.4% 2.8%Grading Tx Early Leaders 200 0 0 0 0.0% 0.0%




Little Bayhorse Lake Mackay 23-Jun-16 None 74 5 0 2 15.7% 11.5% 22.0% 13.6%Perkins Lake Sawtooth 21-Jun-16 None 49 7 0 2 33.3% 20.0% 42.8% 22.4%

06-May-16 None 27 1 1 1 8.6% 14.0% 25.9% 23.6%14-Jun-16 None 25 3 2 0 27.9% 25.4% 46.6% 31.7%17-Jun-16 None 75 11 0 3 34.2% 16.7% 43.5% 18.8%05-Jul-16 None 100 11 0 3 25.6% 12.8% 32.6% 14.4%

02-Aug-16 None 50 2 1 0 9.3% 10.7% 14.0% 13.1%08-Jun-16 None 50 1 0 1 4.7% 7.6% 9.3% 10.7%07-Jul-16 None 75 11 0 2 34.2% 16.7% 40.4% 18.1%

Yankee Fork Dredge Pond (Lower) Sawtooth 03-Aug-16 None 20 3 0 0 34.9% 31.2% 34.9% 31.2%Yankee Fork Pond #1 Sawtooth 03-Aug-16 None 20 4 0 0 46.6% 35.2% 46.6% 35.2%Yankee Fork Pond #4 Sawtooth 03-Aug-16 None 21 3 0 0 33.3% 29.8% 33.3% 29.8%

6

5

7

Squaw Creek Pond Mackay

Valley Creek Sawtooth

Yankee Fork Dredge Pond Sawtooth

Ryder Park Pond American Falls

Wellness Reservoir American Falls

Rock Creek East Fork American Falls

American Falls Reservoir American Falls

30-Aug-16

Rose Pond American Falls 21-Jun-16

26-Apr-16

Blue Creek Reservoir American Falls 25-May-16

Snake River (upper) R5American Falls 31-Aug-16

Treasureton Reservoir Grace 16-May-16

26-Apr-16

Snake River Gem State American Falls 31-Aug-16

16-May-16

Chesterfield Reservoir Grace 16-May-16

Foster's Reservoir Grace 16-May-16

Glendale Reservoir Grace 16-May-16

Horseshoe Lake American Falls 25-May-16

Island Park Reservoir Hagerman 20-Jun-16

Disposition Adjusted Exploitation Adjusted Total UseRegion Water Body Hatchery Tagging

Date Treatment Tags Released

22

Table 5. Total nonreward tags released by water body, hatchery, stocking date, and treatment in 2015. Harvest and Catch were estimated through the second year at large with associated 90% confidence intervals (C.I.).

1 Avondale Lake Sandpoint 21-Sep-15 None 149 2 1 3.0% 3.5% 4.5% 4.3%Snake River American Falls 21-Apr-15 Grading Tx Early Leaders NB 50 1 4.5% 7.3% 4.5% 7.3%

Grading Ctrl 197 1 1.1% 1.9% 1.1% 1.9%Grading Tx Late Leaders 199 1 1.1% 1.9% 1.1% 1.9%

Winchester Lake Hagerman 26-Oct-15 Grading Tx Early Leaders NB 150 1 1.5% 2.5% 1.5% 2.5%Grading Ctrl 200 8 8.9% 5.3% 8.9% 5.3%

Grading Tx Early Laggers 200 3 3.4% 3.2% 3.4% 3.2%Grading Tx Early Leaders 199 1 1 1.1% 1.9% 2.2% 2.6%

Grading Tx Early Leaders NB 199 2 1 2.2% 2.6% 3.4% 3.2%Magnums 270 1 0.8% 1.4% 0.8% 1.4%Standards 270 1 0.8% 1.4% 0.8% 1.4%Magnums 125 1 1.8% 2.9% 1.8% 2.9%Standards 125 2 3.6% 4.2% 3.6% 4.2%

Grading Tx Early Leaders NB 175 1 1.3% 2.1% 1.3% 2.1%Magnums 200 1 1.1% 1.8% 1.1% 1.8%Standards 200 1 1.1% 1.8% 1.1% 1.8%

Dierke's Lake Hagerman 21-Sep-15 Grading Tx Early Laggers 90 1 2.5% 4.1% 2.5% 4.1%Featherville Dredge Pond Hagerman 18-Aug-15 Grading Tx Early Leaders NB 25 1 8.9% 14.5% 8.9% 14.5%

Grading Ctrl 50 1 4.5% 7.3% 4.5% 7.3%Grading Tx Early Laggers 50 2 8.9% 10.3% 8.9% 10.3%

Lake Walcott Hagerman National 15-Sep-15 None 299 17 12.7% 5.3% 12.7% 5.3%Grading Ctrl 180 3 1 3.7% 3.6% 5.0% 4.1%

Grading Tx Early Leaders 175 1 1.3% 2.1% 1.3% 2.1%Grading Tx Late Leaders 178 7 8.8% 5.5% 8.8% 5.5%

Hagerman 20-Apr-15 Grading Tx Early Leaders 297 1 0.8% 1.2% 0.8% 1.2%Magnums 200 7 1 7.8% 4.9% 8.9% 5.3%Standards 200 5 5.6% 4.2% 5.6% 4.2%

Grading Ctrl 75 2 6.0% 6.9% 6.0% 6.9%Grading Tx Early Laggers 75 2 1 6.0% 6.9% 8.9% 8.4%Grading Tx Early Leaders 75 2 1 6.0% 6.9% 8.9% 8.4%

Grading Tx Early Leaders NB 73 4 12.2% 10.0% 12.2% 10.0%American Falls Reservoir American Falls 21-Oct-15 None 457 1 0.5% 0.8% 0.5% 0.8%

Grading Tx Early Leaders 199 1 1.1% 1.9% 1.1% 1.9%Grading Tx Early Laggers 200 1 1.1% 1.8% 1.1% 1.8%

Deep Creek Reservoir Nampa 21-May-15 Cormorant 300 4 3.0% 2.5% 3.0% 2.5%Foster's Reservoir Grace 18-May-15 Cormorant 300 3 2.2% 2.1% 2.2% 2.1%

Glendale Reservoir Grace 18-May-15 Cormorant 300 3 2.2% 2.1% 2.2% 2.1%Johnson Reservoir Grace 18-May-15 Cormorant 300 1 0.7% 1.2% 0.7% 1.2%

Snake River (Above American Falls) American Falls 16-Jun-15 Grading Tx Early Leaders NB 90 1 2.5% 4.1% 2.5% 4.1%Treasureton Reservoir Grace 18-May-15 Cormorant 300 1 0.0% 0.0% 0.7% 1.2%

Ashton Reservoir American Falls 20-May-15 Grading Tx Early Leaders 175 1 1.3% 2.1% 1.3% 2.1%Island Park Reservoir Nampa 25-Jun-15 Magnums 250 1 0.9% 1.5% 0.9% 1.5%

Grading Ctrl 75 1 3.0% 4.9% 3.0% 4.9%Grading Tx Early Leaders NB 75 1 0.0% 0.0% 3.0% 4.9%

22-Sep-15 Grading Tx Early Leaders 75 3 8.9% 8.4% 8.9% 8.4%Little Bayhorse Lake Sawtooth 15-Jun-15 None 50 1 4.5% 7.3% 4.5% 7.3%

29-May-15 None 150 2 3.0% 3.5% 3.0% 3.5%24-Jun-15 None 150 1 1.5% 2.5% 1.5% 2.5%

12-Aug-15 None 100 1 0.0% 0.0% 2.2% 3.7%

90% C.I.


Region Water Body Hatchery Tagging Date


HarvestedHarveste

d b/c tagged

Released Estimate 90% C. I. Estimate

7

Spring Valley Reservoir Hagerman 20-Apr-15

Arrowrock Reservoir Hagerman 26-Oct-15

Lucky Peak Reservoir Nampa7-Apr-15

2

3B

3M

4

5

6

Sage Hen Reservoir Nampa 18-May-15

Warm Lake Nampa 25-Jun-15

Lake Cleveland Hagerman 18-Aug-15


Salmon Falls Creek ReservoirNampa 24-Sep-15

Sublett Reservoir American Falls 20-May-15

Mosquito Flat Reservoir Mackay

Blackfoot Reservoir American Falls 27-Oct-15

Snake River Gem State American Falls16-Jun-15

23

Table 6. Total nonreward tags released by water body, hatchery, stocking date, and treatment in 2016. Harvest and Catch were estimated through the second year at large with associated 90% confidence intervals (C.I.).

Avondale Lake Sandpoint 20-Sep-16 None 193 4 1 4.8% 4.0% 6.0% 4.5%Fernan Lake Sandpoint 12-Apr-16 None 150 1 1.6% 2.6% 1.6% 2.6%

17-May-16 None 151 1 1.5% 2.5% 1.5% 2.5%1-Jun-16 None 147 1 0.0% 0.0% 1.6% 2.6%

2-May-16 None 100 2 4.7% 5.4% 4.7% 5.4%1-Jun-16 None 100 1 2.3% 3.8% 2.3% 3.8%

Spring Valley Reservoir Hagerman 20-Jun-16 Grading Tx Early Leaders NB 98 1 2.4% 3.9% 2.4% 3.9%Winchester Lake Hagerman 24-Oct-16 Grading Ctrl 125 1 1.9% 3.1% 1.9% 3.1%

Grading Ctrl 180 3 3.9% 3.7% 3.9% 3.7%Grading Tx Early Laggers 179 3 1 3.9% 3.7% 5.2% 4.3%Grading Tx Early Leaders 180 1 1 1.3% 2.1% 2.6% 3.0%

Grading Tx Early Leaders NB 178 2 2.6% 3.1% 2.6% 3.1%Grading Ctrl 300 2 1.6% 1.8% 1.6% 1.8%

Grading Tx Early Laggers 294 2 1.6% 1.9% 1.6% 1.9%Grading Tx Early Leaders NB 298 2 1.6% 1.8% 1.6% 1.8%

North Fork Payette River Nampa 22-Jun-16 Magnums 50 1 4.7% 7.6% 4.7% 7.6%Featherville Dredge Pond Hagerman 24-May-16 Grading Tx Early Leaders 40 1 0.0% 0.0% 5.8% 9.5%

21-Sep-16 None 199 1 1.2% 1.9% 1.2% 1.9%12-Oct-16 None 93 1 1 2.5% 4.1% 5.0% 5.8%


Grading Tx Early Leaders NB 100 1 2.3% 3.8% 2.3% 3.8%Mormon Reservoir Hagerman 18-Apr-16 None 200 1 1.2% 1.9% 1.2% 1.9%


Grading Tx Early Leaders NB 125 1 1.9% 3.1% 1.9% 3.1%Grading Ctrl 179 4 1 5.2% 4.3% 6.5% 4.8%

Grading Tx Early Laggers 180 4 5.2% 4.3% 5.2% 4.3%Grading Tx Early Leaders 180 3 3.9% 3.7% 3.9% 3.7%

Grading Tx Early Leaders NB 179 1 1 1.3% 2.1% 2.6% 3.0%Grading Ctrl 90 3 2 7.8% 7.4% 12.9% 9.5%

Grading Tx Early Laggers 90 4 10.3% 8.5% 10.3% 8.5%Grading Tx Early Leaders 90 5 1 12.9% 9.5% 15.5% 10.4%

Grading Tx Early Leaders NB 89 5 13.1% 9.6% 13.1% 9.6%Magnums 200 1 3 1.2% 1.9% 4.7% 3.9%Standards 200 2 2.3% 2.7% 2.3% 2.7%Magnums 200 4 1 4.7% 3.9% 5.8% 4.3%Standards 20 5 58.2% 38.4% 58.2% 38.4%Magnums 200 1 1.2% 1.9% 1.2% 1.9%Standards 200 3 1 3.5% 3.3% 4.7% 3.9%

Rose Pond American Falls 21-Jun-16 Grading Tx Early Laggers 25 1 9.3% 15.1% 9.3% 15.1%Magnums 100 2 0.0% 0.0% 4.7% 5.4%Standards 100 2 0.0% 0.0% 4.7% 5.4%

Wellness Reservoir American Falls 21-Jun-16 Grading Tx Early Laggers 22 1 0.0% 0.0% 10.6% 17.1%Grading Ctrl 196 3 3.6% 3.4% 3.6% 3.4%

Grading Tx Early Leaders 200 1 1.2% 1.9% 1.2% 1.9%Snake River Gem State American Falls 31-Aug-16 Magnums 149 1 1.6% 2.6% 1.6% 2.6%

Chesterfield Reservoir Grace 16-May-16

16-May-16American Falls

Island Park Reservoir Hagerman 20-Jun-16

Treasureton Reservoir Grace 16-May-16

16-May-16GraceGlendale Reservoir

Sublett Reservoir American Falls 25-May-16

American Falls Reservoir

25-Apr-16


Salmon Falls Creek Reservoir Hagerman 25-Apr-16

24-Oct-16

Cascade Reservoir Hagerman 26-May-16

Lake Walcott Hagerman

6

Lower Twin Lake Sandpoint

Mirror Lake Sandpoint

Arrowrock Reservoir Hagerman

Magic Reservoir Hagerman

1

2

3B

3M

4

5

Harvested b/c tagged

Released Estimate 90% C. I. Estimate 90% C.I.


Region Water Body Hatchery Tagging Date


Harvested

24

Table 7. Catch rates for catchable Rainbow Trout reared in baffled and unbaffled raceways at Nampa Fish Hatchery and stocked in 2017. Catch estimates are categorized by water body type and represent tags returned within the first year at-large.

Water body type n Total catch (90% C.I.)

Baffled raceway Unbaffled raceway Ponds 10 33.3% (± 20.7%) 42.1% (± 20.7%) Lakes/reservoirs 10 23.5% (± 7.4%) 19.2% (± 7.3%) Flowing waters 9 15.4% (± 10.0%) 12.2% (± 5.0%)

25

Figure 1. A.) Design of a 3.6-m aluminum baffle installed at Nampa Fish Hatchery. Each

baffle was installed perpendicular to flow and a 13 mm gap was maintained between the bottom edge of the baffle and the raceway floor to increase current velocity and transport waste material. Two openings (61 × 15 cm) were cut along the bottom edge of each baffle to allow fish to move freely within the raceway. B.) Side view of baffle installed into raceway, illustrating the 70° angle created between the back of the baffle and the raceway floor.

26

Figure 2. Catch rates for magnum (total length = 305 mm) and standard (total length = 254

mm) catchables stocked into lakes, reservoirs, and flowing waters across Idaho between 2014 and 2016. Catch was estimated through the first year at-large (i.e., within 365 days of release).

27

Figure 3. Catch rates for magnum (total length = 305 mm) and standard (total length = 254

mm) catchables stocked into lakes, reservoirs, and flowing waters across Idaho between 2014 and 2016. Catch was estimated through the second year at-large (i.e., between 366-730 days of release). No tags were returned during the second year at-large for flowing waters in 2015.

28

Figure 4. Catch rates for catchable Rainbow Trout reared in baffled and unbaffled raceways

at Nampa Fish Hatchery. Fish were stocked in late spring and early summer of 2017 into ponds, lakes, reservoirs, and flowing waters across Idaho. Estimated catch for Heroes pond exceeds 100% due to inherently high catch of tagged fish and a correction factor applied during calculation (see methods).

29

Figure 5. Year-specific angler tag reporting rates. Note: 2017 is a preliminary reporting rate.

0

10

20

30

40

50

60

2011 2012 2013 2014 2015 2016 2017*

Repo

rtin

g ra

te (%

)

Year

30

ANNUAL PERFORMANCE REPORT SUBPROJECT #2: RELATIVE PERFORMANCE OF TRIPLOID KOKANEE SALMON IN

IDAHO LAKES AND RESERVOIRS

State of: Idaho Grant No.: F-73-R-40 Fishery Research Project No.: 4 Title: Hatchery Trout Evaluations Subproject #2: Relative Performance of Triploid

Kokanee Salmon in Idaho Lakes and Reservoirs

Contract Period: July 1, 2017 to June 30, 2018

ABSTRACT

Kokanee Oncorhynchus nerka mature early and typically spawn and die between age-2 and age-4. Due to slow growth, short lifespan, and angler preference for larger fish, kokanee are often only exploited by anglers for a short period of time during their last year of life. Using triploid salmonids in hatchery-supported freshwater fisheries protects native stocks from potential genetic introgression with hatchery fish, but other benefits may include increased longevity, survival, and growth, all of which could improve kokanee fisheries. The objectives of this study were to evaluate whether switching hatchery-supported kokanee waters from diploid to triploid stocking would increase survival, longevity, or growth, as measured by increased catch of larger fish in gill net sampling. Four water bodies were selected for this evaluation: two treatments (Mirror Lake and Montpelier Reservoir) and two controls (Lower Twin Lake and Devils Creek Reservoir). Each water body has been sampled annually since 2012 to describe the existing populations of diploid kokanee and to evaluate triploid growth and survival. Devil’s Creek Reservoir had the largest kokanee, followed by Lower Twin Lake, Montpelier Reservoir, and Mirror Lake. Overall, catch-per-unit-effort and length-at-age estimates were variable among sampling years across all water bodies. Although the final stocking event for this evaluation occurred during spring of 2017, sampling will continue annually at least through July 2018, when the second group of triploid kokanee will have reached age-four to document any increase in longevity or mean fish size in the population. Author: Phil Branigan Senior Fisheries Research Biologist

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INTRODUCTION

Kokanee Oncorhynchus nerka are an important recreational species in reservoirs and lakes across the western United States and Canada (Rieman and Myers 1992). In Idaho, hatchery-reared diploid kokanee are stocked to supplement wild populations and to provide put-grow-take fisheries. Kokanee are often managed to support high yield fisheries or provide a forage base for large piscivores (Wydoski and Bennett 1981). While kokanee are important to the harvest-oriented anglers and for providing trophy fisheries, managing for healthy kokanee populations is often problematic (Beattie and Clancey 1991). Harvest rates of kokanee are heavily influenced by growth rates, population density, and fish size. Since the majority of kokanee populations in Idaho are found in oligotrophic lakes or reservoirs, growth rates can be relatively low, especially when population densities exceed 50 fish/ha (Rieman and Myers 1992). Additionally, kokanee mature early and typically spawn and die at age-3 or age-4 (Johnston et al. 1993). Due to short life span and angler's preference for larger fish, kokanee are often only exploited for a short period of time during their last year of life.

The use of triploid salmonids has become increasingly common in hatchery-supported

freshwater fisheries. Since triploids are functionally sterile, one obvious benefit of stocking triploid fish is genetic protection of wild stocks (Rohrer and Thorgaard 1986). However, it is often asserted that sterility may provide a fisheries or aquaculture benefit (Teuscher et al. 2003), such as increased survival (Ihssen et al. 1990) or growth (Habicht et al. 1994; Sheehan et al. 1999). In kokanee fisheries, enhanced longevity may provide additional sportfishing opportunity in subsequent years after semelparous diploids would have already perished. Indeed, greater longevity could ultimately result in larger size due to a longer growth period and thus increased yield. However, there are drawbacks to stocking triploids, which may include higher mortality and reduced growth during early life-history stages (Myers and Hershberger 1991). Additionally, survival to eye-up for triploid kokanee egg lots may be lower than diploid control groups (Koenig 2011), requiring more eggs to be collected to meet stocking requests.

Post-release performance of sterile kokanee relative to non-sterile conspecifics has rarely

been evaluated. Parkinson and Tsumura (1988) and Johnston et al. (1993) both found increased longevity but no growth advantage for sterilized fish, and the longevity benefit could not overcome the much poorer survival of younger age classes of triploid fish relative to control (diploid) fish. The overall result of these studies was reduced catch for the triploid groups. More recently, researchers in Canada have been experimenting with triploid kokanee in sport fish applications. Initial studies in several lakes stocked only with triploid kokanee indicate triploid fish do not produce the same quality fisheries as lakes stocked exclusively with diploid fish (BC Ministry of Forests, Lands and Natural Resource Operations, Mike Ramsay, personal communication). While these studies provide insight into the utility of sterile kokanee fisheries, results are questionable because each study was performed in only a few lakes, with no definitive marks to differentiate diploid and triploid fish, making comparisons of catch between groups difficult. In addition, Parkinson and Tsumura (1988) and Johnston et al. (1993) compared treatment and control fish stocked in the same lakes, where competition could have been a factor. Finally, the data from BC Ministry of Forests, Lands and Natural Resource Operations do not include information describing the fishery before switching to triploid only. The goal for this study was to definitively evaluate whether switching kokanee fisheries from diploid to triploid would result in greater longevity and better size structure (i.e., more larger fish) to the fishery.

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OBJECTIVES

1. Describe kokanee populations before and after switching to triploid-only stocking relative to control lakes.

2. Increase catch-per-unit-effort (CPUE) of 250 mm (or greater) kokanee by at least 25%. 3. Increase the proportion of “quality” sized kokanee (>300 mm) by at least 25% after

switching to triploid-only kokanee stocking.

METHODS

Study Sites

Since this evaluation focused on comparing fisheries after converting to triploid-only stocking, study sites were chosen from those currently stocked with kokanee. Few locations were suitable for research purposes, as we did not want to risk collapsing any particularly popular sport fisheries, and sites had to be of manageable size for cost and sampling efficiency. Additionally, naturally reproducing populations of kokanee may confound results and make interpreting treatment effects difficult, so lakes thought to have negligible natural spawning production were chosen. Based on these selection criteria, two lakes in southeast Idaho and two from northern Idaho were selected for this study. Waters in each region of the state were paired, such that one water served as a control and the other served as a treatment. Consequently, Mirror Lake and Montpelier Reservoir were randomly selected as treatment waters, whereas Lower Twin Lake and Devils Creek Reservoir served as control waters.

Two years (2012 and 2013) of initial sampling were conducted to describe the existing

populations (length distributions, age classes, growth rates) of diploid kokanee at all four water bodies. After this initial sampling, stocking at the treatment lakes was switched to triploid kokanee, while control lakes continued with normal diploid stocking. Since a particular cohort of kokanee will not fully recruit to the fishery until at least one year after stocking, triploid fish were first stocked in the spring of 2013 in treatment waters.

Egg Collection and Triploidy Induction

The fifth year of triploid treatment and diploid control groups were spawned in September of 2016 during normally scheduled weir operations on the Deadwood River. Triploid production lots were made by applying pressure treatment to eggs on site; eggs were subjected to 9500 psi at 350 Celsius-minutes after fertilization for five minutes. Kokanee from normal production were used for the diploid control groups.

Hatchery Rearing and Stocking

Fertilized eggs were flown to Cabinet Gorge Fish Hatchery where they were reared until the eyed egg stage. Unique, year-specific otolith thermal marks were applied to both diploid and triploid test groups to distinguish them from naturally produced diploid kokanee, and from subsequent year classes to ensure correct age identification. Thermal marks were confirmed prior to stocking. Stocking lots for Devils Creek and Montpelier reservoirs were transferred to Mackay Fish Hatchery to complete rearing, while Cabinet Gorge Fish Hatchery continued rearing kokanee for Mirror and Lower Twin lakes.

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Prior to stocking, 100 triploid and 10 diploid blood samples were collected to evaluate

triploid-induction rates. Blood samples were collected by severing the caudal peduncle of each fish and immersing it in a tube filled with Alsever's solution. Samples were shipped to North Carolina State University for analysis by flow cytometry. At the time of stocking, mean total length (mm) and weight (g) were collected from 100 individual fish in each study group.

Fish Sampling

Kokanee were first collected in 2012 using experimental gill nets, and sampling will continue annually through at least 2018. Net locations for sampling fish in each water were initially randomly assigned, recorded by GPS, and repeated in proceeding years. The limnetic zone of each water body was divided into numbered squares and a random number generator was used to select three squares to serve as the monitoring locations. One net was fished for one night at each of the three locations on each water body, for a total annual fishing effort of three net-nights per water body.

Kokanee were sampled once annually from mid-June to mid-July, after waters had begun

to stratify, around the timing of the new moon phase. Fish were collected by suspending the experimental gill nets at the depth of the thermocline. Each gill net measured 55 m long by 6 m deep. Two of the three nets were “small” mesh composed of panels ranging from 19 to 64 mm bar mesh monofilament; the third net was “medium” mesh composed of panels ranging from 64 to 152 mm bar mesh monofilament. Panels were randomly positioned on nets during manufacturing. Captured kokanee were processed by measuring total length (mm) and weight (g). In addition, otoliths from all fish were extracted and later analyzed in the laboratory to assign ages to each individual fish.

Data Analysis

Standing kokanee stocks before and after switching to triploid-only stocking were described in terms of fish size distribution and catch rates. Mean catch-per-unit-effort (CPUE) for each lake was calculated by summing the catch from each net and dividing by the total number of nets to generate an average catch rate (fish/net-night). Size-at-age and mean total length were used to characterize stock structure in each lake. Sectioned otolith samples were examined to determine fish age, and thermal marks were used to describe the age structure of the populations in each lake.

PRELIMINARY RESULTS / DISCUSSION

Baseline samples of diploid kokanee were collected from all four waters in 2012 and treatment triploid groups were sampled starting in 2013. By 2017, five year classes of treatment fish (age-0, age-1, age-2, age-3, and age-4) should theoretically be present in treatment waters. Age structure of sampled fish was similar in 2017 to previous sample years, with the exception of Devil’s Creek Reservoir where fish older than age-1 have not been sampled since 2014. The lack of fish older than age 1 sampled from Devils Creek Reservoir is likely attributed to fast growth (Table 8). Since 2015, CPUE increased for triploid waters and decreased for diploid waters (Figure 6). Length frequencies and mean-length-at-age were similar to previous years for diploid and triploid waters (Figure 7; Table 8).

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Similar to prior years, length at age was highly variable across waters in 2017. Devil’s Creek Reservoir again showed fast growth while Montpelier Reservoir showed moderate growth (Table 8). Additionally, the larger, faster growing fish of Devil’s Creek Reservoir continue to appear to mature and spawn at an earlier age, as no fish over the age of two have been sampled. Conversely, many age-3 kokanee were sampled in the slow growing Mirror Lake population. Older kokanee age at maturity associated with slower growth rates is well established in the literature (Grover 2005).

For the first time since this study began, age-4 fish were sampled from Mirror Lake in

2017, representing 7% of the overall catch from that system. Thus, there is evidence to suggest that triploidy improved longevity for the kokanee population at Mirror Lake. However, mean length-at-age for age-4 fish was lower than that of age-3 fish, suggesting that there is no growth benefit for fish that survive an extra year. This result may be confounded to some extent by the generally slow growth that is observed for fish of any age at Mirror Lake, and the pattern may instead be driven by annual changes in environmental conditions.

Catch-per-unit-effort remained somewhat consistent from 2012 to 2013, but was

significantly lower in 2014. Since then, CPUE has rebounded for most systems except Montpelier Reservoir, which continued to have the lowest CPUE. Catch rates at Mirror Lake increased during the same time period and have been consistently higher than the control system (i.e., Lower Twin Lake) over the past two sample years.

Since 2015, CPUE has increased at Montpelier Reservoir and Mirror Lake, both triploid

waters. Mean length-at-age for kokanee in Montpelier Reservoir has remained consistent over the past two years while fish at Mirror Lake estimated to be age-2 and older have increased in size. Conversely, fish in Lower Twin Lake have decreased in size over the same time period and no fish over age-1 have been sampled in Devil’s Creek Reservoir since 2014. Future reports will contain more detailed information and 2018 will likely serve as the final year of sampling for this evaluation. Should age-5 fish be sampled in any water body in 2018, sampling will continue in 2019 and beyond until the longevity benefit is fully documented.

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ACKNOWLEDGEMENTS

I would like to acknowledge John Cassinelli, Joe Thiessen, Liz Mamer, Kristi Stevenson, Kevin Nelson, Dennis Daw, Kyle Gatt, Jordan Everson, and Hamish Stevenson for assisting with sample collection. I would like to thank Steve Elle, Kristi Stevenson, Dennis Daw, Liz Mamer, and Kyle Gatt for their help with aging otoliths. I thank Kristi Stevenson, Dennis Daw, and Kyle Gatt for mounting, slicing, and imaging otoliths. I would also like to thank Bob Becker and the staff at Nampa Fish Hatchery for their assistance collecting and pressure shocking Kokanee Salmon eggs at Deadwood Reservoir. Additionally, I would like to thank John Rankin and the staff at Cabinet Gorge Fish Hatchery and Pat Moore and the staff at Mackay Fish Hatchery for their work rearing and releasing fish. I also thank John Cassinelli, Jennifer Vincent, and Beau Gunter for editing this report. Funding for this work was provided by anglers and boaters through their purchase of Idaho fishing licenses, tags, and permits, and from federal excise taxes on fishing equipment and boat fuel through the Sport Fish Restoration Program.

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LITERATURE CITED

Beattie, W. D., and P. T. Clancey. 1991. Effects of Mysis relicta on the zooplankton community and Kokanee Salmon population of Flathead Lake, Montana. American Fisheries Society Symposium 9:39-48.

Grover, M. C. 2005. Changes in size and age at maturity in a population of Kokanee Salmon

Oncorhynchus nerka during a period of declining growth conditions. Journal of Fish Biology 66(1):122-134.

Habicht, C., J. E. Seeb, R. B. Gates, I. R. Brock, and C. A. Olito. 1994. Triploid Coho Salmon

outperform diploid and triploid hybrids between Coho Salmon and Chinook Salmon during their first year. Canadian Journal of Fisheries and Aquatic Sciences 51:31-37.

Ihssen, P. E., L. R. McKay, I. McMillan, and R. B. Phillips. 1990. Ploidy manipulation and

gynogenesis in fishes: cytogenetic and fisheries applications. Transactions of the American Fisheries Society 119:698-717.

Johnston, N. T., E. A. Parkinson, and K. Tsumura. 1993. Longevity and growth of hormone-

sterilized Kokanee Salmon. North American Journal of Fisheries Management 13:284-290.

Koenig, M. K. 2011. Idaho Department of Fish and Game. Annual performance report number 11-

07. Boise. Myers, J. M., and W. K. Hershberger. 1991. Early growth and survival of heat shocked and

tetraploid-derived triploid Rainbow Trout. Aquaculture 96:97-101. Parkinson, E. A., and K. Tsumura. 1988. Growth and survival of hormone-sterilized Coho

Oncorhynchus kisutch and Kokanee Salmon O. nerka in a lacustrine environment. Canadian Journal of Fisheries and Aquatic Sciences 45:1490-1494.

Rieman, B. E., and D. Myers. 1992. Influence of fish density and relative productivity on growth

of Kokanee Salmon in ten oligotrophic lake and reservoirs in Idaho. Transactions of the American Fisheries Society 121:178-191.

Rohrer, R. L., and G. H. Thorgaard. 1986. Evaluation of two hybrid trout strains in Henry’s Lake,

Idaho, and comments on the potential use of sterile triploid hybrids. North American Journal of Fisheries Management 6:367-371.

Sheehan, R. J., S. P. Shasteen, A. V. Suresh, A. R. Kapuscinski, and J. E. Seeb. 1999. Better

growth in all-female diploid and triploid Rainbow Trout. Transactions of the American Fisheries Society 128:491-498.

Teuscher, D. M., D. J. Schill, D. J. Megargle, and J. C. Dillon. 2003. Relative survival and growth

of triploid and diploid Rainbow Trout in two Idaho reservoirs. North American Journal of Fisheries Management 23:983-988.

Wydoski, R. S., and D. H. Bennett. 1981. Forage species in lakes and reservoirs of the western

United States. Transaction of the American Fisheries Society 110:764-771.

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Table 8. Net-hours, CPUE, and age distribution of diploid (2N) and triploid (3N) Kokanee Salmon in two control and two treatment lakes for sample years 2012-2017. Gray shaded values represent age classes that are triploid.

Water Body Sample Year Treatment Net-

Hours CPUE Mean-Length-At-Age (mm) Age-0 Age-1 Age-2 Age-3 Age-4

Montpelier Res.

2012

3N

105.8 1.63 109 271 336 338 NA 2013 54.5 1.27 112 220 274 NA NA 2014 40.0 0.65 105 228 282 314 NA 2015 41.3 0.58 NA 252 NA NA NA 2016 41.3 0.84 96 151 270 324 NA 2017 45.6 0.66 96 245 277 323 NA

Mirror Lake

2012

3N

46.5 4.10 100 160 205 246 NA 2013 45.5 4.37 104 159 205 235 NA 2014 47.3 1.27 103 188 190 240 NA 2015 47.1 1.74 125 198 221 NA NA 2016 43.7 3.43 112 203 251 259 NA 2017 48.8 3.43 102 159 238 271 255

Devils Creek Res.

2012

2N

49.1 3.60 121 317 459 NA NA 2013 47.0 4.68 115 317 467 500 NA 2014 45.3 1.08 103 294 449 NA NA 2015 44.5 1.87 102 285 NA NA NA 2016 41.3 0.34 116 NA NA NA NA 2017 46.3 1.12 97 311 NA NA NA

Lower Twin Lake

2012

2N

89.8 3.00 106 293 389 NA NA 2013 45.0 1.82 104 289 393 NA NA 2014 48.5 0.72 97 263 387 NA NA 2015 47.9 7.62 136 317 380 NA NA 2016 45.3 1.81 NA 254 332 312 NA 2017 48.2 1.70 96 266 333 NA NA

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Figure 6. Relative abundance (fish/net hr) of Kokanee Salmon sampled from 2012-2017 among four study waters.

0

1

2

3

4

5

6

7

8

Montpelier Res. Devils CreekRes.

Mirror Lake Lower TwinLake

CPU

E (fi

sh/n

et h

r)2012

2013

2014

2015

2016

2017

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Figure 7. Length distribution (by percent) of Kokanee Salmon across four water bodies. Distributions represent samples taken in

the summer of 2012-2017.

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ANNUAL PERFORMANCE REPORT SUBPROJECT #3: PERFORMANCE OF DIPLOID AND TRIPLOID WESTSLOPE

CUTTHROAT TROUT STOCKED INTO IDAHO ALPINE LAKES

State of: Idaho Grant No.: F-73-R-40 Fishery Research Project No.: 4 Title: Hatchery Trout Evaluations Subproject #3: Performance of Diploid and Triploid

Westslope Cutthroat Trout Stocked Into Idaho Alpine Lakes

Contract Period: July 1, 2017 to June 30, 2018

ABSTRACT

Anglers value alpine lakes as a scenic, backcountry fishing experience seldom found in other fisheries. However, trout introduced into alpine lakes sometimes pose a risk to native salmonids in downstream habitats by establishing source populations in headwater locations. While stocking sterile triploid trout can reduce this risk, post-stocking performance should be equivalent to diploid fish before fisheries managers and anglers consider triploid stocking ideal. In this study, three different mechanical pressure treatments were tested to create mixed-sex triploid Westslope Cutthroat Trout Oncorhynchus clarkii lewisi; triploid induction rates were 100%, and egg survival to eye-up was only 8% lower for triploids than for diploids. Fry were stocked into 51 alpine lakes (25 with triploids and 26 with diploids), and fish were sampled three years later. Gill net catch rates, growth, and condition did not differ between stocked diploid and triploid fish. General linear models revealed that test fish were larger in lakes with fewer fish (indicating a density dependent influence on growth), and were in better condition in lower elevation lakes containing a higher percentage of shallow habitat with fewer total fish. Ploidy level was not included in the most plausible model for any of the response variables. Our results indicate that triploid Westslope Cutthroat Trout can easily be created using pressure treatment of fertilized eggs, and are a suitable alternative to diploids in alpine lake stocking programs. As such, the use of triploid trout in alpine lakes would prevent hybridization with native salmonids in adjacent habitats without sacrificing fishing quality in the lakes where they are stocked.

Authors: John Cassinelli Regional Fisheries Biologist Kevin A. Meyer Principal Fisheries Research Biologist Martin K. Koenig Sportfish Program Coordinator Ninh V. Vu Fisheries Research Biologist Matthew R. Campbell Genetics Program Coordinator

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INTRODUCTION

Historically, most alpine lakes in western North America were fishless (Dunham et al. 2004). However, over the last century many of these lakes have been stocked with hatchery trout in an effort to diversify angling opportunities. Alpine lakes provide a unique fishing opportunity with solitude, dramatic scenery, and a backcountry experience seldom found in other fisheries. Not surprisingly, anglers visiting alpine lakes typically express high levels of satisfaction with their fishing experience (WGF 2002; IDFG 2007). However, trout introduced into alpine lakes pose a potential risk to native salmonids by establishing source populations in headwater locations that are often able to migrate downstream and potentially hybridize and compete with native fish (reviewed in Dunham et al. 2004).

The use of triploid hatchery trout in alpine lake stocking programs is one way to prevent

nonnative salmonids from establishing undesirable wild populations because triploid salmonids are functionally sterile. Triploid fishes are commonly produced by heat- or pressure-shocking eggs soon after fertilization (reviewed in Maxime 2008 and Piferrer et al. 2009), but recipes that result in 100% triploid induction can vary even for species in the same family (e.g., Benfey and Sutterlin 1984; Piferrer et al. 1994; Cotter et al. 2000; Kozfkay et al. 2005) and have not yet been perfected for various salmonids including Cutthroat Trout (Kozfkay et al. 2006). Treatments to induce triploidy consistently reduce egg and sac fry survival (e.g., Happe et al. 1988; Guo et al. 1990), though performance differences between diploid and triploid fish from button-up to stocking size are generally less consistent (Withler et al 1998; Wagner et al. 2006; Taylor et al. 2011).

While previous studies have shown variability in pre-release performance between diploid

and triploid fish, most studies investigating fishery performance after stocking have found reduced survival for triploids. Reduced post-release survival for triploid fish has been demonstrated for Rainbow Trout Oncorhynchus mykiss in particular (Simon et al. 1993; Brock et al. 1994; Koenig et al. 2011; Koenig and Meyer 2011) but also for Coho Salmon O. kisutch (Rutz and Baer 1996) and Atlantic Salmon Salmo salar (Cotter et al. 2000). Reduced triploid survival has been attributed to a combination of having fewer red blood cells, lower total blood hemoglobin (Benfey and Sutterlin 1984; Benfey 1999), a reduced hemoglobin–oxygen loading capacity (Graham et al. 1985), and reduced anaerobic capacity (Hyndman et al. 2003; Scott et al. 2014). Differences in survival as a result of these physiological shortcomings become most apparent when triploid hatchery trout are stocked in challenging conditions such as waters with low dissolved oxygen (Simon et al. 1993; Yamamoto and Iida 1994) or higher temperature (Ojolick et al. 1995). Hatchery trout are often stocked in chronically stressful waters because wild trout typically cannot support a robust fishery in such environments. While pristine in setting, alpine lakes can be challenging environments for hatchery trout due to short growing seasons, inconsistent food sources, and low dissolved oxygen during winter months (Donald and Anderson 1982; Bailey and Hubert 2003).

Although reduced post-release survival for triploid hatchery trout should be expected, it is

not a foregone conclusion. In fact, some studies have demonstrated equivalent post-stocking survival for diploid and triploid trout stocked in lotic (Dillon et al. 2000) and lentic settings (Teuscher et al. 2003). In aquaculture settings, triploid fish have a growth advantage over diploid fish because they do not expend energy on gonadal development (Ihssen et al. 1990), though such growth advantages have rarely manifested themselves in the wild (Ojolick et al. 1995; Koenig et al. 2011; Koenig and Meyer 2011; but see Teuscher et al. 2003). In addition to differences in growth and survival between diploid and triploid fish, behavioral differences have also been noted. Of particular interest is a study that found that while both diploid male and female Brook Trout Salvelinus fontinalis emigrated from Adirondack lakes during spawning, only male triploids emigrated (Warrillow et al. 1997). This suggests that stocking triploids could result in a

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higher percentage of stocked fish remaining in alpine lakes once stocked, potentially maintaining higher trout densities over the long term.

None of the above mentioned diploid-triploid post-release comparisons have been

conducted on Cutthroat Trout. The Idaho Department of Fish and Game currently stocks about 700 of the state’s estimated 3,000 alpine lakes, often using diploid Westslope Cutthroat Trout O. clarkii lewisi. Downstream migration of these fish could lead to hybridization with native stocks of Westslope Cutthroat Trout and Redband Trout O. mykiss gairdneri. Thus managers are faced with the quandary of being reluctant to stock diploid Cutthroat Trout in headwater lakes due to hybridization concerns, while also being reluctant to stock triploid fish if they provide an inferior fishery for alpine lake anglers. Considering the remaining uncertainty with regard to triploid post-stocking performance, the following objectives were established for this study: (1) develop a “recipe” for Westslope Cutthroat Trout triploidy using mechanical pressure treatment, (2) compare the survival, growth, and condition of mixed-sex triploid and diploid Westslope Cutthroat Trout fry stocked into alpine lakes, and (3) evaluate whether environmental factors influence survival, growth, and condition of diploid and triploid Westslope Cutthroat Trout in alpine lakes.

METHODS

Triploid Recipe Development

Westslope Cutthroat Trout stocked throughout Idaho originate from the Idaho Department of Fish and Game’s brood stock facility at Cabinet Gorge Fish Hatchery, and were initially derived from the King’s Lake stock in British Columbia. An experiment to induce triploidy in Westslope Cutthroat Trout eggs was conducted at the hatchery in 2010 using hydrostatic pressure. Previous pressure treatment studies have shown that the duration and level of applied pressure are relatively consistent between species, but the time post-fertilization to most effectively inhibit the shedding of the third polar body can be variable (Kozfkay et al. 2006). Therefore, three treatments were tested using the same pressure (9,500 psi) and treatment duration (5 minutes), but the pressure treatment was applied at three different times after fertilization, those being 300, 350, and 400 Celsius-minutes-after-fertilization (CMAF, water temperature × time). There were three replicates of each treatment and a control. Eggs from 19-23 females were pooled together for each replicate. Approximately equal numbers of eggs were split four ways (three treatments and one control) from the pooled eggs, and then fertilized using pooled milt from 4-5 males and activated with water.

Surviving eggs were reared to approximately 50 mm at which time blood samples were

collected to determine triploid induction rates via flow cytometry. Blood was collected by caudal severance, stored in Alsever’s solution, and shipped to North Carolina State University where ploidy levels were determined with flow cytometry. Up to 50 blood samples were collected per treatment replicate where possible, but some replicates with poor survival had as few as 20 fish remaining, in which case all fish were sampled. The triploid induction rate was determined as the proportion of fish that were triploid out of the total tested in each replicate. Confidence intervals (95%) around the triploid proportion were calculated according to the methods outlined in Fleiss et al. (2003).

Egg Collection / Rearing

In 2011 and 2013, triploid eggs were created at Cabinet Gorge Fish Hatchery using standard spawning techniques followed by pressure treatment to induce triploidy. Approximately

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120 female Westslope Cutthroat Trout were used to collect about 100,000 triploid eggs to then rear to fry, assuming roughly 50% survival to the eyed-egg stage (based on previous salmonid triploid experience). Batches of eggs from 20-30 females were pressure treated to induce triploidy using the most successful pressure treatment derived above. Diploid fish were obtained in the same fashion, with the exception of the pressure treatment process. These fish were reared separately from the triploid group. After eye-up, eggs were transferred to the McCall Fish Hatchery for rearing.

Both diploid and triploid test fish were marked with adipose fin clips while rearing at McCall

Fish Hatchery to differentiate them from previously stocked or naturally produced trout in our study lakes. Prior to stocking, 100 triploid and 10 diploid blood samples were collected to estimate triploid induction rates using the same methods described above. Just prior to stocking, fish from both the triploid and diploid groups were sampled to characterize mean length (mm), weight (g), and relative weight (Wr) using the formula:

𝑊𝑊𝑟𝑟 = (𝑊𝑊/𝑊𝑊𝑠𝑠) ∗ 100,

where W = actual fish weight, and Ws = a standard weight for fish of the same length (Anderson and Neumann 1996).

A total of 51 lakes were stocked with test fish (26 with diploids and 25 with triploids) by

use of fixed-wing aircraft as part of the routine 2011 and 2013 (August and September) stocking requests for the specified lakes. Study lakes were chosen throughout central Idaho to encompass a wide geographical range and variable physiochemical habitat characteristics, but sampling efficiency (i.e., distance from trailhead, and some targeted clustering of lakes to maximize data collection for each field trip) was also considered when selecting study lakes. Diploid and triploid marked fish were stocked into separate lakes to avoid any potential competition between the ploidy test groups that might influence performance and survival (Kozfkay et al. 2006; Koenig et al. 2011). The number of marked trout stocked in each lake was determined by the standard annual request for that location, resulting in a wide range of stocking densities (34 to 1,429 fish/acre).

Post-Stocking Evaluation

All lakes were sampled three years after stocking so stocked fish could grow to a size desirable to anglers. Two, three, or four floating experimental gill nets were set per lake depending on lake size. Gill nets (46 m long and 1.5 m deep) consisted of nylon mesh panels of 19, 25, 30, 33, 38, and 48 mm bar mesh; they were set perpendicular to the shoreline in mid- to late afternoon and retrieved the following morning. Captured fish were identified to species, checked for an adipose fin clip, measured to the nearest mm (total length), and weighed to the nearest g. In 2016, a tissue sample was taken from all adipose-clipped trout to genetically assign sex to test fish and determine if there were any differences in sex ratios between diploid and triploid groups.

Several lake characteristics were measured (Table 9) that have been previously shown to

be related to trout size (length or weight) and abundance in alpine lakes (e.g., Donald et al. 1982; Chamberlain and Hubert 1996; Rabe 2001; Bailey and Hubert 2003). Elevation (m) and surface area (km2) were determined using Google Earth Pro (Google Inc. 2013). Shoreline development – measured as the length of the shoreline (as the numerator) divided by two times the square root of the surface area of the lake times pi – is a measure of the amount of shoreline relative to the size of the lake, with perfect circles having a value of 1.0; this measurement was also taken from Google Earth Pro. Aspect, which affects solar input, and therefore productivity in alpine lakes,

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was categorized as best (south facing lakes), excellent (SW and SE facing), good (E and W), fair (NE and NW), and poor (N). Stocking density was calculated as the number of fish stocked divided by the estimated surface area (fish/km2). Lake distance (km) from the nearest maintained trail was also measured from maps and was used as an index of angler accessibility. At the time of the fish surveys, an estimate of the percent of shallow water (i.e., <1-2 m deep) in the lake was visually estimated because shallower lakes are generally more productive.

Genetic Analyses

Restriction site associated DNA sequencing was used to identify sex-specific markers to estimate the proportion of captured test fish in 2016 that were males or females. This method uses a restriction enzyme to cut the genome of reference males and females and then sequence 100-300 base pairs that flank the restriction site and the resulting DNA fragments. This technology is a particularly powerful tool for exploring genetic variation in ‘nonmodel’ species because it does not require a fully sequenced genome (Gamble and Zarkower 2014). We screened 10 phenotypic males and 10 phenotypic females using the Pst-I restriction enzyme. We identified two single nucleotide polymorphic (SNP) markers - WCT_245656_41 and WCT_138669_65 - that yielded patterns of high genotyping success and differentiated genetic sex in test samples. These SNP markers were converted into taqman assays (primer/probe sequences and PCR conditions available from authors upon request). The accuracy of these markers was further tested with a screening of 90 phenotypic females and 90 phenotypic males from the Kings Lake stock of Westslope Cutthroat Trout. Of the 180 samples, 175 (97.2%) exhibited concordance between phenotypic sex and genetic sex. All five of the discrepancies were from phenotypic males that genotyped as genetic females. Because 100% concordance was observed among genotyping calls between the two markers, only WCT_138669_65 was screened on study samples.

Data Analyses

Prior to stocking, the mean length and mean Wr of test fish was compared using t-tests. For post-stocking evaluations, each lake was considered the unit of observation for all analyses. For each lake, catch-per-unit-effort (CPUE) was calculated as the catch rate of study fish per net-hour fished; CPUE was considered an index of the abundance of study fish in the lake. There was strong correlation between catch/hr and catch/net-night (r = 0.93), thus data analyses were essentially identical regardless of which catch metric was used. Mean fish length and mean Wr of test fish were also estimated for each lake as indices of fish growth and fish condition. Two-sample t-tests were used to assess whether CPUE, mean length, and mean Wr differed between diploid and triploid groups.

To evaluate whether lake characteristics affected CPUE, growth, or condition of test fish,

all independent variables (i.e., lake characteristics) were first plotted individually against all three response variables (CPUE, mean length, and mean Wr) to look for data outliers, nonlinear relationships, and heteroscedasticity. Because naturally-produced or previously-stocked trout were encountered in 46 of the 51 study lakes, the CPUE of non-test fish was included as a predictive variable to account for potential density dependent effects on the abundance of stocked test fish. For mean length and mean Wr analyses, density dependence was evaluated by relating these two metrics to CPUE of all fish sampled; scatterplots indicated these two relationships were nonlinear, thus CPUE of all fish sampled was given a natural logarithm transformation prior to the remaining analyses.

General linear models were then developed for each response variable separately.

Candidate models for each response variable were limited to all potential single-factor models,

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as well as the best multifactor model if that model was superior to any of the single-factor models. Candidate models were ranked using Akaike’s Information Criterion corrected for small sample size (AICc; Burnham and Anderson 2002), and the amount of variation explained by each model was compared using the coefficient of determination. Ploidy was also included as an explanatory variable, and year was included because of the difference in fish condition at time of stocking between years.

A two-proportion z-test (Fleiss et al. 2003) was used to evaluate whether the sex ratio was

skewed toward females in triploid lakes compared to diploid lakes, as would result if diploid males and females both engaged in spawning migrations that resulted in some emigration from lakes, but for triploid fish, only males engaged in such migrations (Warrillow et al. 1997). Because such an effect would only increase the female sex ratio in triploid lakes relative to diploid lakes (not decrease it), a one-tailed test was conducted. All analyses were conducted using the SAS statistical software package (SAS 2009) with α = 0.05.

RESULTS

Triploid Recipe Development

Triploid induction rates were very similar across all three treatments (Table 10). The 300 and 350 CMAF treatments both showed 100% triploid induction rates across all replicates. The 400 CMAF treatment had only slightly lower triploid induction (98% on average). Survival to eye-up was highest for the control group (31% on average), followed by the 300 CMAF test group (27% on average). Mean survival to eye-up was much lower for the 350 CMAF (16%) and 400 CMAF (18%) test groups. Eye-up rates were low for all egg lots from Replicate 1, including controls, suggesting poor egg quality for that group. When not including eggs from Replicate 1, mean eye-up rates were much higher, ranging from 21% to 38%. The 300 CMAF treatment (9,500 psi, 5 minutes) returned the best combination of induction rate and survival to eye-up; therefore, this treatment was used to develop triploid eggs for the rest of our study.

Egg Collection / Rearing

For the 2011 egg take, eye-up rates between the two study groups were similar to those observed during recipe development trials, with triploid eye-up rate (41%) being slightly lower than for diploids (48%). For eggs collected in 2013, eye-up rates were higher and virtually identical for diploids (57%) and triploids (56%). Triploid induction rates were 100% in both 2011 and 2013.

At the time of stocking, the average length and Wr of diploid fish in 2011 (42.8 mm and

121.5, respectively) were very similar to that of triploid fish (44.2 mm and 112.9); neither the length (t = 1.33; P = 0.18) nor the Wr (t = 1.21; P = 0.23) of test fish differed statistically between ploidy groups. In 2013, the average length of diploid fish (42.0 mm) and triploid fish (41.1 mm) again did not differ statistically (t = 1.77; P = 0.08); however, the mean Wr of diploid fish (130.4) and triploid fish (80.8) differed statistically (t = 35.93; P <0.001; Figure 8).

Post-Stocking Evaluation

A total of 1,372 trout were caught in gill nets across all 51 test lakes, 24% of which were test fish; the remaining fish were mostly wild trout although some were previously stocked hatchery trout. Of the 26 lakes stocked with diploid trout, 22 contained study fish, while 19 of the 25 triploid lakes contained study fish.

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Mean CPUE across both study years was 0.16 fish/hr for diploid test fish compared to

0.15 fish/hr for triploid test fish, and did not differ statistically between the two ploidy groups (t = 0.40; P = 0.69). Average length at each lake was 291 mm for both diploid and triploid test fish and obviously did not differ statistically between ploidy groups (t = 0.01; P = 0.99). Mean Wr of test fish was 97.5 for lakes stocked with diploid test fish and 96.2 for lakes stocked with triploid test fish. The slightly higher diploid Wr was not statistically different (t = 0.35; P = 0.73).

The general linear models developed to analyze factors potentially influencing CPUE,

mean length, and Wr in alpine lakes showed that most factors we measured had little to no effect on the post-stocking performance of test fish (Table 11). For the CPUE models, the best model indicated that catch of test fish was higher at lakes with more shoreline relative to the size of the lake. There was over 10 times more support for this model than the next best three models, which collectively indicated that catch of test fish was higher at smaller lakes with a higher percentage of shallow habitat and when catch of non-test fish was lower. However, even the best model explained only 11% of the variation in CPUE of test fish between lakes.

For the fish length models, the best model indicated that test fish were larger in lakes with

fewer total fish, and explained 28% of the variation in mean fish length across all lakes. There was very little support for any other models.

For Wr, the best model indicated that test fish condition was higher in lower elevation lakes

containing a higher percentage of shallow habitat, with fewer total fish, and that were stocked in 2011 (rather than 2013). The best model explained 39% of the variation in mean Wr of test fish, and there was very little support for any other models.

Thus density dependence was most evident in fish growth and condition models and only

slightly supported in the abundance models; this was also evident when examining scatterplots alone (Figure 9). Ploidy was not included in the most plausible model (based on AICc weights) for any of the response variables.

Results from fish sampled in 2016 showed that sex ratios of adult study fish remaining in

lakes was variable (Figure 10). Overall, the proportion of the catch that was female in triploid lakes (55%) was slightly higher than in diploid lakes (48%), but did not differ statistically (z = 0.80, P = 0.21). Thus there was no evidence that a higher proportion of diploid females were emigrating from lakes relative to triploid females.

DISCUSSION

Hydrostatic pressure treatment proved to be an effective way to create triploid hatchery Westslope Cutthroat Trout, and our recipe was similar to those previously found to be effective for various salmonids (Teskeredžić et al. 1993; Kozfkay et al. 2005, 2006). As expected, triploid green-egg to eyed-egg survival was slightly lower, but this can usually be mitigated for during the egg take process by spawning more fish. Prior to stocking, fish condition was lower for triploid fingerlings in one year, but this did not result in reduced post-stocking fish condition. Previous work comparing pre-stocking hatchery growth of diploid and triploid trout has been highly variable, with some studies demonstrating that triploid hatchery trout grew better than diploids prior to stocking (Simon et al. 1993; Sheehan et al. 1999) and other studies demonstrating the opposite effect (Myers and Hershberger 1991) or no difference (Wagner et al. 2006). Considering this variability in pre-stocking performance between studies, and potential low triploid egg eye-up

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rates, hatchery staff should closely monitor growth and survival of triploid trout in-hatchery to meet stocking goals typically set for diploids.

Three years after stocking them into alpine lakes, mixed-sex triploid Westslope Cutthroat

Trout had equivalent survival, growth, and condition compared to diploids. These results concur with a previous study demonstrating equivalent performance of mixed-sex triploid and diploid Brook Trout stocked in alpine lakes (Budy et al. 2012), but contrast a study in which diploid Rainbow Trout survival was higher than for mixed-sex triploids stocked in mountain lakes (Koenig et al. 2011). Authors of the latter study suggested that because diploid and triploid fish were stocked into the same waters in their study, competition rather than inherently lower performance may have explained the differential survival they observed, but authors of the former study directly evaluated some aspects of competition and observed no differences between diploids and triploids in diet or aggressive behavior. In the present study, by stocking groups independently, year-class specific competition was removed as a potential confounding factor. Assuming that catchability by anglers does not differ between diploid and triploid fish (Dillon et al. 2000), stocking triploid Westslope Cutthroat Trout in alpine lakes should produce the same angler satisfaction as diploid stocking, with the added benefit that adjacent native salmonid populations face little to no conservation threat.

Out-migration of trout stocked in alpine lakes has been documented by other authors

(Warrillow et al. 1997; Adams et al. 2001; Daniels et al. 2008) and can create two potential problems, both of which can be circumvented by stocking triploid fish. First, stocking triploids reduces the potential risk of out-migrating fish colonizing adjacent waters and threatening the persistence of native salmonids via competition or introgressive hybridization. Second, while sterile males display external sexual characteristics, and migrate to spawning areas at rates similar to diploid males, sterile females may not (Warrillow et al. 1997). Thus the use of all-female triploid trout in alpine lake stocking programs could potentially halt spawning-related out-migration altogether. In fact, all-female triploid Rainbow Trout stocked in alpine lakes outperformed diploid and mixed-sex triploid fish by a 3:1 and 11:1 ratio, respectively (Koenig et al. 2011), although what role out-migration played in these differences was not investigated. While not statistically different in the present study, the slightly higher percentage of females (determined genetically) in triploid waters - relative to diploid waters - was intriguing, but this slight skewness was not statistically significant and was in the same direction as the genotype:phenotype discordance mentioned above. Having sampled at three years after stocking, we may have collected fish too early to detect a significant shift in sex ratios, though the size and age of our test fish should have resulted in most fish being mature. Further research on gender-specific out-migration rates, and the feasibility of creating all-female fry for stocking, is needed to determine if the excess costs and labor of creating all-female triploids is justified by a higher percentage of stocked trout remaining in receiving waters for anglers to catch.

With a robust sample size of lakes and wide range in stocking densities in our study, we

anticipated some sort of density-dependent relationship between stocking density and CPUE (cf. Bailey and Hubert 2003) that might provide managers with better guidelines on how many fish to stock in a given alpine lake. However, stocking density explained none of the variability in CPUE of stocked Westslope Cutthroat Trout and little of the variability in their growth and condition. Any relationship between stocking density and stocked fish abundance in the present study may have been masked by the fact that 76% of the fish caught were non-test fish; thus, in most cases the number of fish stocked had little influence on total fish abundance in the lake. Nevertheless, there was a strong density-dependent response of test fish growth and condition to the total number of fish caught (Figure 9); such density-dependent signals are common in alpine lake trout fisheries

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(Hall 1991; Walters and Post 1993; Parker et al. 2007; Messner 2017), though predation on stocked fry may also have played a role.

Although we admittedly measured only some of the environmental variables that have

been previously shown to influence salmonid growth and survival in alpine lakes, the only metrics that had any appreciable relationship to post-stocking performance of Westslope Cutthroat Trout were elevation, the percentage of the lake that was shallow, and the amount of shoreline relative to the size of the lake. In particular, lower elevation lakes grew larger fish with better condition, as has been demonstrated previously for mountain lakes (Donald et al. 1980). While elevation likely did not have a causative effect on fish growth or condition, elevation is often correlated with other physiochemical conditions in alpine lakes that we did not measure, such as water temperature and conductivity, both of which have been shown to affect fish growth in alpine lakes (Donald et al. 1980; Chamberlain and Hubert 1996; Bailey and Hubert 2003). Shallow habitat has long been associated with increased lake productivity for fish (Moyle 1949; Northcote and Larkin 1956), including alpine lakes (Chamberlain and Hubert 1996).

This study indicates that mixed-sex triploid Westslope Cutthroat Trout are a viable

alternative to diploids for fisheries managers to utilize as a put-and-grow stocking tool in alpine lakes where the conservation of adjacent native salmonid populations is a concern. Egg takes associated with triploid groups should be adjusted to compensate for slightly less survival to eye-up. Further research comparing mixed-sex and all-female Westslope Cutthroat Trout post-release performance may be warranted to evaluate whether the added cost of developing an all-female strain would be outweighed by the added survival other studies have demonstrated for all-female strains (e.g., Koenig et al. 2011).

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ACKNOWLEDGMENTS

We acknowledge the staffs at Cabinet Gorge and McCall fish hatcheries for their work in spawning, rearing, marking, and stocking the WCT used in this study. Luciano Chiaramonte, Micah Davidson, Dennis Daw, Leah Gunnink, Pat Kennedy, Tony Lamansky, Liz Mamer, Kevin Nelson, Kylie Porter, Rick Raymondi, Dan Schill, Noah Starr, Luke Teraberry, Joe Thiessen, Jennifer Vincent all assisted with lake sampling. Robert Hand and Dale Allen and their field crews also helped with additional lake sampling. We thank Dan Schill for critically reviewing an earlier version of the manuscript. Funding for this work was provided by anglers and boaters through their purchase of Idaho fishing licenses, tags, and permits, and from federal excise taxes on fishing equipment and boat fuel through the Sport Fish Restoration Program.

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Table 9. Means and ranges of lake and fish characteristics measured at 51 alpine lakes in Idaho where either diploid or mixed-sex triploid Westslope Cutthroat Trout were stocked and sampled three years later. CPUE is catch-per-unit-effort (fish/hr), and Wr is relative weight.

Table 10. Percent eye-up and percent triploidy (with upper and lower 95% confident intervals) for controls and three pressure treatments of fertilized Westslope Cutthroat Trout eggs treated at 9,500 for 5 minutes at varying Celsius-minutes-after-fertilization (CMAF).

Diploid lakes Triploid lakesLake characteristics Mean Min Max Mean Min MaxElevation (m) 2,226 1,639 2,472 2,201 1,345 2,525Surface area (ha) 3.1 0.5 11.7 3.8 0.4 12.1Percent shallow habitat 0.21 0.02 0.80 0.22 0.03 1.00Stocking density (Number/acre) 237 38 1235 224 34 1429Distance from nearest trail (km) 3.1 0.0 11.0 3.6 0.0 12.0CPUE of test fish 0.16 0.00 0.50 0.15 0.00 0.52Total length of test fish 291 217 372 140 220 353Wr of test fish 98 75 116 96 77 129CPUE of non-test fish 0.58 0.00 3.02 1.20 0.00 2.59

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Table 11. Model results relating catch-per-unit-effort (CPUE), fish length, and relative weight of test fish to various lake and fish characteristics at 51 alpine lakes in Idaho stocked with either diploid or mixed-sex triploid Westslope Cutthroat Trout fry and sampled three years later.

Model AICc ΔAICc weight r2

Catch-per-unit-effort modelsBest: Shoreline development -140.86 0.00 0.68 0.11CPUE of non-test fish -135.74 5.12 0.05 0.02Surface area -135.73 5.13 0.05 0.02Percent shallow habitat -135.50 5.36 0.05 0.02Elevation -134.88 5.98 0.03 0.00Distance from nearest trail -134.85 6.01 0.03 0.00Stocking density -134.76 6.10 0.03 0.00Ploidy -134.75 6.11 0.03 0.00Year -134.70 6.16 0.03 0.00Aspect -132.80 8.06 0.00 0.10

Fish length modelsBest: Ln(CPUE of all fish) 335.66 0.00 0.98 0.28Aspect 345.25 9.59 0.01 0.19Elevation 346.14 10.48 0.01 0.09Stocking density 346.99 11.32 0.00 0.07Shoreline development 348.38 12.72 0.00 0.04Percent shallow habitat 349.24 13.58 0.00 0.02Year 349.44 13.78 0.00 0.02Surface area 349.47 13.80 0.00 0.02Distance from nearest trail 349.88 14.21 0.00 0.01Ploidy 350.16 14.50 0.00 0.00

Relative weight modelsBest: Ln(CPUE of all fish) + year + percent shallow habitat + elevation 214.11 0.00 0.96 0.39Ln(CPUE of all fish) 221.67 7.56 0.02 0.16Elevation 223.09 8.98 0.01 0.15Year 224.19 10.08 0.01 0.12Stocking density 227.49 13.38 0.00 0.04Distance from nearest trail 227.68 13.57 0.00 0.04Percent shallow habitat 228.72 14.61 0.00 0.01Ploidy 229.09 14.98 0.00 0.00Surface area 229.22 15.11 0.00 0.00Shoreline development 229.22 15.11 0.00 0.00Aspect 232.79 18.68 0.00 0.00

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Figure 8. Relative weights of juvenile diploid (2N) and mixed-sex triploid (3N) Westslope Cutthroat Trout prior to stocking in 2011 and 2013.

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Figure 9. Scatterplots of potential density-dependent relationships for catch-per-unit-effort, mean length, and relative weight (Wr) for diploid (open circles) and mixed-sex triploid (filled circles) Westslope Cutthroat Trout stocked in 51 alpine lakes in Idaho and sampled three years later. Correlation coefficients (r) and least-squares linear regression lines are also depicted.

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.00 1.00 2.00 3.00 4.00

Test

fish

cau

ght/

hr g

ill n

ettin

g

Non-test fish caught/hr gill netting

r = -0.14

70

80

90

100

110

120

130

-3.00 -2.00 -1.00 0.00 1.00

Mea

n W

rof

test

fish

Ln (total fish caught/hr gill netting)

r = -0.43

200

250

300

350

400

-3.00 -2.00 -1.00 0.00 1.00

Mea

n le

ngth

of t

est f

ish (m

m)

Ln (total fish caught/hr gill netting)

r = -0.55

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Figure 10. Sex composition of diploid and triploid Westslope Cutthroat Trout stocked in 51 alpine lakes in Idaho in 2013 and sampled three years later.

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Prepared by: Approved by: IDAHO DEPARTMENT OF FISH AND GAME Phil Branigan Jeff C. Dillon Fisheries Research Biologist Fisheries Research Manager James P. Fredericks, Chief Bureau of Fisheries

PROJECT 4: HATCHERY TROUT EVALUATIONS...catchables across 24 Idaho lakes and reservoirs and 19...

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Transcript of PROJECT 4: HATCHERY TROUT EVALUATIONS...catchables across 24 Idaho lakes and reservoirs and 19...