long-term effects of size- selective fisheries & hatchery mating practices on age & sex...
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LONG-TERM EFFECTS OF SIZE-SELECTIVE FISHERIES & HATCHERY MATING PRACTICES ON AGE & SEX COMPOSITION OF CHINOOK SALMON RETURNING TO HATCHERIES David Hankin & Jackie Fitzgibbons
Fisheries Biology
Humboldt State University, Arcata, CA
LIFE HISTORY OF CHINOOK SALMON
Anadromous and Semelparous Age at Maturity:
Males: Ages 2 (“jacks”) through Age 6
Females: Ages 3 through Age 6 Female Age Composition is used to Classify
Stock-Specific Maturation Schedule (Early-, Mid-, and Late-Maturing).
In Wild Populations, Percentages of Males at Age are Not Tightly Correlated with
Proportions of Females at Age
FEMALE AGES STREAMS MALE AGES
3 4 5 6 2 3 4 5 6
50 44 5 1 Applegate 33 39 26 2 0
0 20 73 7 Nehalem 4 23 31 42 0
2 33 43 21 Trask 0 12 62 20 6
4 30 58 9 Salmon 35 22 28 13 2
Hatchery Production is HUGE:
• California’s Central Valley (Sacramento River):
32 million fish
• OR/WA Columbia River Hatcheries: 150-180 million fish
AGE AT MATURITY IS AN INHERITED TRAIT THAT IS STRONGLY INFLUENCED BY PARENTAL AGES
ELK RIVER HATCHERY AGE AT MATURITY EXPERIMENTS:
Hankin et al. 1993. Evidence for inheritance of age at maturity in chinook salmon. CJFAS.
Elk River Hatchery Experiments
Age-Specific Mating Experiments:
1974 BY: 3 x 3 VS 5 x 5
1979 BY: 2 x 4+ VS 4+ x 4+
1980 BY: 2 x 4+ VS 4+ x 4+
2 3 4 5 6
AGE
0
400
800
1200
Est
imate
d R
iver
Retu
rns
at
Age
1974 BY: 3x3 vs 5x5
Female Returns: 3x3Female Returns: 5x5
2 3 4 5 6
AGE
0
1000
2000
3000
Est
imate
d R
iver
Retu
rns
at
Age
1974 BY: 3x3 vs 5x5
Male Returns: 3x3Male Returns: 5x5
2 3 4 5 6
AGE
0
50
100
150
Obse
rved R
iver
Retu
rns
at
Age
1979 BY: 2x4+ vs 4+x4+
Female Returns: 2x4+Female Returns: 4+x4+
Spawning Behavior Research Suggests that Larger Males Enjoy Greater
Reproductive Success (Baxter HSU)
MANAGEMENT ISSUES AND MODELING QUESTIONS
Does size-selective ocean fishing, through shifting age composition of spawners to younger ages, select for earlier age at maturity (Ricker 1980, 1981)?
Does random mating of hatchery fish, especially random inclusion of jacks as male parents, cause unintentional (genetic) selection for earlier age at maturity (Hankin 1986-present!)?
KEY MODEL FEATURES
Matrixes of Conditional Maturation Probabilities – Device to Account for Heritability of Age at Maturity
Age- and Sex-Structured Model of a Hatchery Chinook Salmon Population That Incoporates:
1. Hatchery Mating Practices, & 2. Size-Selective Ocean Fisheries
Example Matrixes of Conditional Maturation Probabilities: AT AGE 2, FOR MALES
MALE PARENT AGE
FEMALE PARENT AGE
2 3 4 5 6
3 0.5810 0.2997 0.1786 0.0574 0.0287
4 0.5428 0.2800 0.1688 0.0536 0.0268
5 0.5280 0.2600 0.1549 0.0498 0.0249
6 0.4652 0.2400 0.1430 0.0460 0.0223
Example Matrixes of Conditional Maturation Probabilities: AT AGE 3, FOR FEMALES
MALE PARENT AGE
FEMALE PARENT AGE
2 3 4 5 6
3 0.4026 0.3103 0.2182 0.1280 0.0604
4 0.2740 0.2112 0.1484 0.0856 0.0429
5 0.1456 0.1122 0.0789 0.0455 0.0228
6 0.0726 0.0567 0.0394 0.0228 0.0140
MODEL ASSUMPTIONS
REASONABLE ASSUMPTIONS
Hatchery matings are all 1:1 No females mature at age 2 All eggs are equally likely to survive to age 2 50:50 sex ratio in ocean at age 2
MODEL ASSUMPTIONS
“SIMPLIFYING” ASSUMPTIONS
No Freshwater Harvest Size at age k is independent of parental ages Ocean exploitation rates are constant and do
not vary between years
Model Parameters
p1 = probability of survival from egg to age 2
pk = (conditional) probability of surviving from age k to k+1
iF(i,j) = conditional probability of a female maturing at age i given
age i male and age j female parents
uk = ocean exploitation rate at age k
fj = average number of eggs per age j female
max = maximum number of eggs that can be hatched and reared
MODEL SCENARIOS
UNEXPLOITED VS EXPLOITED HATCHERY MATING POLICY:
1. Completely Random Mating of All Adults, Including Jacks; OR
2. Completely Random Mating Except for Some Selection Against Jacks.
Modeling Results % Jacks in Returns (Unexploited)
1/Z ('Systematic Jacks') or Y ('Maximum Jacks')
Per
cent
age
Jack
s20
2530
3540
1.00 0.75 0.50 0.25 0.10
Other Age Groups Should Also Be Affected By Jack Mating Policy (Unexploited Equilibrium)
2 3 4 5 6
010
30
Male Age at Maturity
Per
cent
of
Ret
urns Random Matings
1/Z=0.25Y=0.1No Jacks Used
2 3 4 5 6
010
30
Female Age at Maturity
Per
cent
of
Ret
urns
Exploitation and Random Mating Together Shift Age Structure Toward Males & Younger Ages
2 3 4 5 6
020
4060
Male Age at Maturity
Per
cent
of
Ret
urns
Unexploitedu3=.2, u4=.35u3=.3, u4=.53
2 3 4 5 6
020
4060
Female Age at Maturity
Per
cent
of
Ret
urns
Selection Against Jacks Can in Part Compensate for Age Structure Shifts Due to Ocean Fishing
Proportion of Jacks Used as Male Parents (1/Z)
Per
cent
Jac
ks in
Pop
ulat
ion
2030
4050
60
1.00 0.75 0.50 0.25 0.10
Unexploited
Moderate Exploitation
Heavy Exploitation
2 3 4 5 6
020
40
60
Male Age at Maturity
Perc
ent
of
Retu
rns
Unexploitedu3=.2, u4=.35u3=.3, u4=.53
Completely Random Mating
2 3 4 5 6
020
40
60
Male Age at Maturity
Perc
ent
of
Retu
rns
No Jacks Used
Jack Mating Policy Effects on Age Composition are not Limited to Age 2 Males: Male Returns
Jack Mating Policy Effects on Age Composition are not Limited to Age 2 Males: Female Returns
3 4 5 6
010
2030
Female Age at Maturity
Per
cent
of
Ret
urns
Unexploitedu3=.2, u4=.35u3=.3, u4=.53
Completely Random Mating
3 4 5 6
010
2030
Female Age at Maturity
Per
cent
of
Ret
urns No Jacks Used
Conclusions from Modeling
Completely Random Mating Should Theoretically Select for Early Age at Maturity.
Jack Usage is Critical in An Early-maturing Stock Type.
“Different” Hatchery Mating Protocols Might Mitigate, in Part, for Fishery Selection?
NEED MORE MATING EXPERIMENTS!!
MORE DIFFICULT QUESTIONS TO ANSWER IN FUTURE:
How does size-selective ocean fishing affect long-term trends in age at maturity in wild population with non-random mating?
How much additional selective effect due to mating policy and inheritance of age at maturity vs. direct selective effects of “fishing down”?