Salmon age and size at maturity: Patterns and processes

1. Age Designation 2. Variation among populations

1. Latitude 2. Within regions 3. Within watersheds

3. Variation within populations 1. Smolt size 2. Growth rate 3. Non-anadromy

4. Size – Sex Ratio 5. Catch vs. Spawning Population 6. Declines in Size and/or Age

Age Designation The total age of the fish does not capture important life history events. Rather, we need to indicate the periods of time spent in freshwater and at sea to distinguish fish of the same age with different life histories. In addition, we need a way to account for the period of time spent as a developing embryo and alevin. There are two distinctly different but equivalent ways in which salmon ages are commonly designated (plus a third used in Russia).

Age Designations: for example, a sockeye salmon

Years spent Designation Fresh- water

Salt-water

U.S. (European)

Canadian (Gilbert-Rich)

Total Age

1 2 1.2 42 4 1 3 1.3 52 5 2 2 2.2 53 5 0 1 0.1 21 2 0 2 0.2 31 3

N.B. These “years” are really winters as a free-swimming fish.

This includes the “missing” year in embryonic stages.

Age Designations

Years spent Designation Fresh- water

Salt-water

U.S. (European)

Canadian (Gilbert-Rich)

Total Age

1 2 1.2 42 4 1 3 1.3 52 5 2 2 2.2 53 5 0 1 0.1 21 2 0 2 0.2 31 3

Age Designations

Years spent Designation Fresh- water

Salt-water

U.S. (European)

Canadian (Gilbert-Rich)

Total Age

1 2 1.2 42 4 1 3 1.3 52 5 2 2 2.2 53 5 0 1 0.1 21 2 0 2 0.2 31 3

Age Designations

Years spent Designation Fresh- water

Salt-water

U.S. (European)

Canadian (Gilbert-Rich)

Total Age

1 2 1.2 42 4 1 3 1.3 52 5 2 2 2.2 53 5 0 1 0.1 21 2 0 2 0.2 31 3

Age Designations

Years spent Designation Fresh- water

Salt-water

U.S. (European)

Canadian (Gilbert-Rich)

Total Age

1 2 1.2 42 4 1 3 1.3 52 5 2 2 2.2 53 5 0 1 0.1 21 2 0 2 0.2 31 3

Features used for Age Determination:

1. Otoliths (ear bones): Record information

during embryonic stages, permanent, but necessitate lethal or post-mortem sampling

2. Scales: not deposited until some period of growth has taken place, can fall off and get replaced, but can be removed from live fish

Aside: Otoliths are mineral and generally yield no DNA but scales can yield DNA from decades past, before DNA was discovered.

Age 1.2 sockeye salmon, Bristol

Bay

focus

Freshwater check

First marine check

Second marine check at the edge

FW 1

SW 1

SW 2

SW 3

Age 1.3 Bristol Bay sockeye

salmon

Age 4 steelhead from Forks Creek: Michael Dauer

1st winter in FW

2nd winter in SW

2nd winter in FW

1st winter in SW

Scale focus

Emerged in 1997

Smolted in 1998

Winter of 1999 at sea

Winter of 2000 at sea

Spawned in 2001

Returned in 2002

Repeat spawning hatchery steelhead from Forks Creek: Michael Dauer

Returned in 1996

Returned in 1998

Returned in 1997

Emerged in 1992

Winter 1995 at sea

Winter 1993 in fresh water

Winter 1994 in fresh water

Wild steelhead: three time spawner

For steelhead and other iteroparous species, the age designation must indicate spawning events as well as the years spent in freshwater and at sea. A 4-year old fish on its first return might be a 1.3 if it went to sea at age 1 but a fish of the same age that spawned in the previous year would be designated 1.1S1. Repeat spawners are smaller than “maidens” of the same age. Michael Parker

Distribution of sockeye salmon by total age in the Chignik Lake system, AK

0.055.63

56.78

37.12

0.430

10

20

30

40

50

60

3 4 5 6 7

Total Age

% o

f run

Dahlberg (1968)

Distribution of Chignik Lake system sockeye salmon by age group

0.05 0.05 0.0035.58

10.68

0.32

46.1

26.27

0.26 0.53 0.1705

101520253035404550

1.1 2.1 3.1 1.2 2.2 3.2 1.3 2.3 3.3 1.4 2.4

Age Group

Mea

n %

of r

un

jacks

Ocean age 1

Ocean age 2

Ocean age 3

Ocean age 4

0.0

0.2

0.4

0.6

0.8

1.0

320 370 420 470 520 570 620 670

Fork length (mm)

Prop

ortio

n su

rviv

ing

to s

paw

n

0

1000

2000

3000

4000

5000

Fecu

ndity

Survival to spawningFecundity

Hypothesized costs in mortality and benefits in fecundity of marine residence

Overall length varies greatly among populations: Mean lengths of North American Chinook salmon

populations

05

10152025303540

400 450 500 550 600 650 700 750 800 850 900Post-orbit to hypural length (mm)

Num

ber

of p

opul

atio

ns

malesfemales

Roni 1992

Kitsumkalum River chinook salmon

Levels of variation in age and size at maturity among populations

• Latitude • Regional features • Local features

Are all the big salmon are in Alaska? Not necessarily.

Roni 1992

Examination of Chinook salmon did not yield any clear trend of size with latitude once age had been accounted for. Coho salmon seem to be larger in Alaska but this does not seem to have been documented, and pink and chum are often smaller in Alaska than farther south, at a given age.

Puget Sound, ca. 50 cm)

Pink salmon weight and chum salmon length (e.g., age-4) decreases with latitude

00.5

11.5

22.5

3

Arctic

Bristol B

ay

Alaska

Peninsula

Kodiak

Prince W

illiam

Sound

SE Alask

a

N Brit

ish C

olumbia

S Brit

ish Columbia

Fraser

River

Washington

Oregon

Pink

sal

mon

wei

ght (

kg)

550600650700750800

Chu

m s

alm

on le

ngth

(mm

)

pink weightchum length

The area where salmon enter the ocean has little effect on their final body size. Small-bodied populations may be located near large-bodied ones, so the differences in size must be related to other things.

Fishing districts

Togiak

Nushagak

Ugashik

Egegik

Naknek-Kvichak

Iliamna Lake

Kvichak River

Naknek River

Wood River

Bristol Bay

District System 2 3Naknek-Kvichak Alagnak 58 41

Kvichak 83 17Naknek 34 65total 70 30

Nushagak Igushik 26 74Nushagak 15 85Wood 54 46total 42 58

Sockeye salmon ocean age varies among districts within Bristol Bay, and among river

systems within districts Ocean age (%)

Older and larger fish tend to predominate in larger rivers (e.g., Wood River sockeye) but they

have access to the same growing conditions

0

20

40

60

80

100

A and Ccreeks

HansenCreek

Bear Creek Ice Creek AgulowakRiver

% o

cean

-age

3 s

alm

on Stream width (m) in the

Wood River system

1.8 3.8

5.1 15.1

77.3

Some individuals and populations tend to grow faster than others. In addition, individuals and populations differ in the “norm of reaction” between growth and maturation. That is, growing at the same rate, some will mature in the next year whereas others with stay at sea, grow larger, and mature at an older age. Really big fish are not faster growing.

Male chinook salmon

Age 4

Age 1

What controls age at maturity within populations?

• Growth in freshwater or smolt size • Growth at sea • Genetics

Coho smolt Chinook

Back-calculated lengths of Chinook salmon (in mm) at different ages, as a function of their final age at

maturity (data from Parker and Larkin 1959).

AGE Age at maturity

Sample 2 3 4 5 6

2 4 266 3 27 220 508 4 150 183 466 676 5 60 171 425 622 813 6 8 122 368 549 730 917

Lengths of Asian chum salmon sampled at sea that were maturing or immature at successive ages. Maturing fish were consistently larger than the

immature fish of their age.

250

350

450

550

650

750

2-May 1-May 1-May 1-May

Fork

leng

th (m

m)

immaturematuring

LaLanne 1971

Not only growth rate at sea but smolt size affects age at maturity. Fish that mature at an early age generally were older/larger as smolts

(e.g., Wood River sockeye salmon).

0

20

40

60

80

100

1 2 3

Age-1 smolts

Age-2 smolts

Number of years spent at sea before returning

% o

f eac

h m

arin

e ag

e gr

oup

Age 4

Age 3

Age 2

Age 1

Mature male UW Chinook salmon

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25

Average smolt weight (g)

% o

f mal

es

age 1 jacksall jacks

Average smolt weight affected the percent of male UW Chinook that matured as jacks and especially age-1 “mini-jacks”

The tendency of female UW Chinook to mature at age 3 rather than age 4 was also related to average smolt weight

0

20

40

60

80

100

0 5 10 15 20 25

Average smolt weight (g)

% a

ge 3

fem

ales

Size, sex and survival • In most populations, the sex ratio is nearly

50:50, and males are slightly larger for their age than females (Why?)

• In many coho salmon populations, males out-number females but are smaller

• So, do females incur a higher mortality associated with their larger size? And why are females larger than males in coho, but smaller in sockeye salmon, for example?

N.B. Fishing rate on jacks is low, so surveys in streams inflate their apparent abundance.

Insert photo of adult coho and jack

Is there also a genetic control over age at maturity?

Do jacks beget jacks?

Females mated with jack Chinook salmon produced more jacks and fewer old males than

females mated with older males

0

20

40

60

80

2 3 4 5 6

Age at maturity of males

% o

f adu

lt of

fspr

ing

2 x 4+

4+ x 4+

Hankin et al. 1993.

Sired by jacks Sired by

older males

Genetic control over age at return

in steelhead

Ocean age of parents

2 3

2 57.0 43.0

3 20.6 79.4

Ocean age of offspring (%)

Tipping 1991

Fisheries can be selective with respect to size, and thus age (e.g., Nushagak River

female sockeye in 1984)

0

0.2

0.4

0.6

0.8

1

485 495 505 515 525 535 545 555 565 575 585 595 605

Escaped

Caught

Prop

ortio

n ca

ught

or e

scap

ing

Length

Further complexities • There may be non-anadromous

individuals (typically males) in anadromous populations

• Variation in size within non-anadromous populations related to food resources, selection from physical habitat limitation, predation risk, etc.

Cedar River 1 + Chinook salmon smolt

Cedar River precocious male Chinook salmon

Large-bodied rainbow trout from British Columbia

Resident cutthroat trout

Genetic and Environmental Factors Influencing Age and Size at Maturity

Age at Maturity: Primarily represents a trade-off between the reproductive benefits of increased size against the risk of mortality in the next year. Age at maturity is negatively related to growth rate or size at age.

Size at Age: Results from 1) natural selection

from factors associated with reproductive success, predation, and physical features of the migratory route and spawning grounds, and

2) environmental influences on growth rate.

Declines in size or age at maturity have been recorded in many populations

r2 = 0.56

400

450

500

550

600

650

700

1950 1960 1970 1980 1990 2000

Ave

rage

Len

gth

(mm

)

UW female coho salmon

Possible reasons for declines in size and age at maturity (Ricker 1980)

1. Biased data 1. Fish caught earlier in the season 2. Fish caught in the year prior to maturity

2. Genetic changes 1. Selective loss of large-bodied populations 2. Fishing selects for fish that mature early in life 3. Size selective fishing selects for small/young fish

3. Environmental changes 1. Changes in temperature affect growth and maturation 2. Changes in density affect growth and maturation

4. Effects of hatcheries 1. Large smolts mature at an earlier age than small ones 2. Selection for large fish actually selects for slow growth