Salmon age and size at maturity: Patterns and processescourses.washington.edu/fish450/Lecture...
Transcript of Salmon age and size at maturity: Patterns and processescourses.washington.edu/fish450/Lecture...
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