David Hankin & Jackie Fitzgibbons Fisheries Biology

1. 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

2. FUNDING: THANKS TO - THE YUROK TRIBE & THE TRINITY RIVER RESTORATION PROGRAM

3. 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).

4. Female Age Composition in Several Oregon Coastal Streams Early- Mid- Late-

5. In Wild Populations, Percentages of Males at Age are Not Tightly Correlated with Proportions of Females at Age

6. Size at Age Increases Dramatically Through Age 4, Then More Slowly

7. Late-Maturing Stocks Produce the Largest Fish (Kenai R., Alaska)

8. Ocean Fisheries Can Dramatically Reduce the Probability of Spawning at an Old Age

9. Hatchery Production is HUGE: • California’s Central Valley (Sacramento River): 32 million fish • OR/WA Columbia River Hatcheries: 150-180 million fish

10. Recreational and Commercial Fisheries are Intensive

11. 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.

12. 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+

17. Spawning Behavior Research Suggests that Larger Males Enjoy Greater Reproductive Success (Baxter HSU)

20. 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!)?

21. 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

22. Example Matrixes of Conditional Maturation Probabilities: AT AGE 2, FOR MALES

23. Example Matrixes of Conditional Maturation Probabilities: AT AGE 3, FOR FEMALES

24. 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

25. 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

26. Model Variables, Model Parameters, & Model Form: Model Variables

27. Model Parameters p1= probability of survival from egg to age 2 pk = (conditional) probability of surviving from age k to k+1 siF(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 Qmax = maximum number of eggs that can be hatched and reared

28. Model Form

31. 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.

32. Modeling Results% Jacks in Returns (Unexploited)

33. Other Age Groups Should Also Be Affected By Jack Mating Policy (Unexploited Equilibrium)

34. Exploitation and Random Mating Together Shift Age Structure Toward Males & Younger Ages

35. Selection Against Jacks Can in Part Compensate for Age Structure Shifts Due to Ocean Fishing

36. Jack Mating Policy Effects on Age Composition are not Limited to Age 2 Males: Male Returns

37. Jack Mating Policy Effects on Age Composition are not Limited to Age 2 Males: Female Returns

38. 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!!

39. 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”?

40. MORE DIFFICULT QUESTIONS TO ANSWER IN FUTURE: • How is “size at age” inherited and to what degree does it influence maturation?