Determining Sex Ratios and Sexual Maturities of Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) in the Saco River, ME

Carolyn Wheeler1, Marine Sciences 2015; Caitlyn Little1, MS; Gail Wippelhauser2, Ph.D.; Gayle Zydlewski3, Ph.D.; Michael, Kinnison3 Ph.D.; James Sulikowski1, Ph.D. 1University of New England, Biddeford, ME; 2Maine Department of Resources, Augusta, ME; 3University of Maine, Orono, ME

.

Introduction The Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) (fig. 1A) is a long-

lived, anadromous fish species ranging from Labrador, CA to Florida, USA

(Status Review Team (ASSRT), 2007). In the Saco River, located in the Gulf

of Maine, Atlantic sturgeon were common in the 1920’s, but were extirpated

by the 1950’s due to overfishing (fig. 1B). However, after a 60 year absence,

Atlantic sturgeon reappeared in the Saco River

in 2007. Although the reason for the return of

this species to this river system remains

unknown, research on basic life history

information is necessary to facilitate the

conservation of this federally protected species.

Understanding reproductive parameters such as sex ratios and sexual

maturities are vital to effective management of any species. Unfortunately,

this information is typically obtained by lethal, gross dissection, or stress

inflicting endoscopy. Thus, in order to better understand these important

life history parameters in Atlantic sturgeon, three non-invasive techniques

(steroid hormone analysis, ultrasonography, and external morphological

features) have been developed (Webb et al., 2002; Petochi et al., 2011;

Vecsei et al., 2003).

These three methods are considered valid however, each technique has

its limitations when used alone. For example, when using ultrasound

imaging immature male and female sturgeon may show similar internal

morphological features, making it difficult to decipher sex (Petochi et al.,

2011). While in steroid hormone analysis, both mature males and females

typically contain elevated concentrations of testosterone and estradiol

respectively, which is an indication if an individual is male and female

(Webb et al., 2002). However, immature individuals typically have low

amounts of testosterone and estradiol, leading to inconsistencies in

determining sex. When each of these techniques is used individually,

misidentifications can be as high as 20%. Therefore, the aim of this study is

to combine these three aforementioned techniques to increase the accuracy

of sex determination to 90%.

By using the three non-lethal techniques of ultrasound, steroid hormone

analysis and external morphological features in combination, three major

questions will be addressed:

(1) What is the sex ratio of Atlantic sturgeon in the Saco River?

(2) What is the maturity states of these individuals (i.e. immature or

mature)?

(3) If mature, are the fish in spawning condition?

Methods

Capture

Atlantic sturgeon were collected using 6-inch and 12-inch gillnets,

two to three times a week using the University of New England’s research

vessel from April to November in 2013.

Conservation Implications Because of the endangered and threatened statuses of sturgeon

populations in the United States, new accurate methods are needed to assess

populations for better management. By utilizing ultrasound imaging, RIA

and external morphological features for the first time together on Atlantic

sturgeon, this project will produce accurate results while eliminating

inaccuracies of each individual method. This validation will give way to a

comprehensive understanding of the Saco River population, which can be

utilized in evaluating other sturgeon and fish populations. Overall, the

return of Atlantic sturgeon to the Saco River

indicates the increased health of the

river system, as well as the recovery of

the East Coast population.

Acknowledgements I would like to thank:

• Dr. James Sulikowski and his lab team

• NOAA Section Six Funding

• The University of New England Summer Undergraduate Research Experience (SURE)

References Cicia AM, Driggers III WB, Ingram GW Jr., Kneebone J, Tsang PCW, Koester DM, Sulikowski JA. 2009. Size and age estimates at sexual maturity for

the little skate Leucoraja erinacea from the western Gulf of Maine, U.S.A. Journal of Fish Biology, 75: 1648-1666.

Petochi, B. T., Di Marco, P., Donadelli, V., Longobardi, A., Corsalini, I., Bertotto, D., Finoia, M.G. and Marino, G. 2011. Sex and reproductive stage

identification of sturgeon hybrids (Acipenser naccarii × Acipenser baerii) using different tools: ultrasounds, histology and sex steroids. Journal of

Applied Ichthyology, 27: 637–642.

Status Review Team (ASSRT). 2007. Status review of Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus). Report to National Marine Fisheries Service,

Northeast Regional Office (0).

Sulikowski JA, Driggers III WB, Ingram GW Jr., Kneebone J, Ferguson DE, Tsang PCW. 2007. Profiling plasma steroid hormones: a non-lethal

approach for the study of skate reproductive biology and its potential use in conservation management. Environmental Biology of Fish, 80(2-3): 285-

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Vecsei P, Litvek MK, Noakes DLG, Rein T, Hochleithner M. 2003. A non-invasive technique for determining sex of live North American sturgeons.

Environmental Biology of Fish, 68: 333–338 .

Webb, M. A., Feist, G. W., Foster, E. P., Schreck, C. B., & Fitzpatrick, M. S. 2002. Potential classification of sex and stage of gonadal maturity of wild

white sturgeon using blood plasma indicators. Transactions of the American Fisheries Society, 131(1), 132-142.

Results

Figure 1: (A) An Atlantic Sturgeon (Acipenser oxyrinchus oxyrinchus)

(B) Atlantic sturgeon caught in Maryland in 1901 (http://www.nccoast.org/)

Objectives

Figure 4: Ultrasound images of (A) immature male sturgeon

showing distinct boundaries and echogenic (bright) margins, (B) a

mature male sturgeon showing distinct margins, and lobulated and

smooth testes, (C) an immature female sturgeon that is

heterogenic and lamellated in shape with indistinct margins and

the ovary is more hyperechoic than the abdominal muscles, and

finally (D) a mature female sturgeon with light, granulated and

echogenic ovaries, that also exhibits ovarian folds.

A B

C D

Sexual Maturities

Sample Collection

At the time of capture, physical measurements were recorded and

blood was drawn from the caudal vein of each sturgeon using a needle and

vacutainer (fig. 2A) and placed on ice. Using an Ibex Pro portable

ultrasound with a convex

transducer, the

sturgeon were placed

with the ventral side up

to view gonads (fig 2B).

Finally, the urogential

region of each individual

was examined for

shape (Fig. 3).

Figure 2: (A) A caudal venous puncture to collect a large blood sample.

(B) An ultrasound being conducted on an Atlantic sturgeon ventrally.

A B

Radioimmunoassay

The frozen plasma

was processed via

radioimmunoassay (RIA)

following techniques

modified from Sulikowski

et al (2007) and Cicia et al

(2009). Figure 3: Urogential opening shapes of a male (A) and female (B).

A B

Ultrasonography

After sampling, ultrasound images were analyzed using a scoring

method where three categories will be evaluated: shade, fat amount

(immature sturgeon)/texture (mature sturgeon) and gonadal margins.

Figure 5: Overall for the 2012 and 2013 sampling seasons,

from RIA only, there was 50% females, 32% males and 18%

unknown. This unknown category is from individuals where

sex could not be determined by RIA independently. With the

addition of the ultrasonography and external morphological

data the unknown category will be reduced to under 10%.

Figure 6 : Sex percents of immature (<100 cm TL), maturing (100-150 cm TL) and mature (>150 cm TL)

Atlantic sturgeon based on RIA data only. These percentages indicate that maturing individuals have the

highest unknown rate due to many gonadal changes caused by large amounts of hormone activity.

Seasons

Figure 7: Sex percents by seasons sampled (March-November) based on RIA data only. These percentages

indicate that there is a large amount of males present in the Saco River in the fall and more females in the

summer months.

A

B