Fishery selection on Alaskan sockeye salmon and potential changes in size at maturity

1. Fishery selection on Alaskan sockeye salmon and potential changes in size at maturity Neala Kendall Tom Quinn School of Aquatic and Fishery Sciences University of Washington

2. Need for quantifying harvest selection • Life history traits are changing over time (Darimont et al. 2009 PNAS)

3. Need for quantifying harvest selection • Life history traits are changing over time (Darimont et al. 2009 PNAS) • Importance of quantifying harvest selection (Carlson et al. 2007 Ecology Letters, Edeline et al. 2007 PNAS)

4. Need for quantifying harvest selection • Life history traits are changing over time (Darimont et al. 2009 PNAS) • Importance of quantifying harvest selection (Carlson et al. 2007 Ecology Letters, Edeline et al. 2007 PNAS) • Evaluating implications of selection (Olsen et al. 2004 Nature, Heino and GodØ 2002 Bulletin of Marine Science)

5. Fishery selectivity curve Fish caught Length Hutchings, Nature 2005 Difficult to quantify fishery selection ?

6. Alaska salmon: good model to study fishery selection Semelparous and anadromous Length and age at maturity easy to measure Know population size and structure Long-term gillnet fisheries Large, long term data set J. Carter

7. Research questions Does fishery selection vary by fish length and sex? J. Carter

8. Research questions Does fishery selection vary by fish length and sex? Are fish length at age changes over time correlated with fishery selection? J. Carter

9. Alaskan gillnet sockeye salmon fisheries Upper Cook Inlet Bristol Bay

10. Methods • Yearly historical fishery reconstruction • Characterize annual length distributions in catch, escapement, and total run • Estimate: 1) Length-specific vulnerability 2) Selection differentials

11. Length frequency histogram example Males Females

12. Vulnerability profiles by length 1990 2002 2003 1994 1999 1 Females 0 1 Males 0 650 650 650 400 400 400

13. lengthescapement – lengthtotal run std. deviation of lengthtotal run Selection on length: SSDs Standardized selection differential = Smaller fish are escaping to spawn than are getting caught Larger fish are escaping to spawn than are getting caught SSD + -

14. Female SSDs more consistently negative than male SSDs Female average Male average J. Carter

15. Fishery selection on Bristol Bay sockeye salmon and length at age changes over time

16. Bristol Bay, Alaska fishing districts

17. Differential fishery selection on ocean age 2 fish Nushagak Nushagak P = 0.143 P < 0.001 Ugashik P = 0.051 P < 0.001 Naknek-Kvichak Naknek-Kvichak P < 0.001 P < 0.001 Proportion frequency Proportion frequency Togiak P = 0.756 P = 0.010 Egegik P = 0.002 P < 0.001 Standardized selection differential Standardized selection differential

18. Average length of ocean age 2 fish has decreased over time 550 Nushagak slope=-0.60 Ugashik slope=-0.16 550 slope=-0.64 slope: P = 0.003 450 Naknek-Kvichak slope=-0.26 slope=-0.16 slope: P = 0.218 Average length (mm) 450 Togiak slope=-0.19 550 Average length (mm) slope=-0.05 slope: P = 0.033 slope=-0.21 Egegik slope=-0.31 550 slope: P = 0.869 450 slope=-0.21 slope: P = 0.005 450

19. SSDs somewhat correlated with decreasing length at age over time

20. Run sizes/harvest rates vary Average fish sizes vary Fishing regulations (mesh size, timing, breaks between fishing periods) vary Why different selection among fishing districts and over time? Conclusions Conclusions

21. Fish caught Conclusions Conclusions Conclusions • Are larger than average fish more vulnerable to being caught? YES

22. Conclusions • Does the fishery harvest different lengths of males than females? Males YES Females Length

23. Are fish length at age changes over time correlated with fishery selection? Conclusions Fishing districts that harvest larger fish show a greater decline in fish length at age over time YES… Other factors, such as ocean temperature and competition, also affect growth But…

24. What can fishery managers do? Escapement counts Exploitation rate Fishery selectivity Time

25. Future work • Create quantitative genetics models to understand impacts of fishery selection and environmental factors on length at age at maturation • Calculate maturation reaction norms for spawning populations to understand potential genetic changes associated with fishery selection • Using estimated selectivities, model ideal length and age at maturity under different harvest scenarios J. Bennis J. Bennis J. Bennis J. Carter

26. Tim Baker and Fred West, ADFG Mark Willette and Terri Tobias, ADFG Jeff Hard, NOAA Fisheries Alaska Salmon Program, UW Funding: School of Aquatic and Fishery Sciences Alaska Sustainable Salmon Fund National Science Foundation Gordon and Betty Moore Foundation Acknowledgements

28. Differential fishery selection on ocean age 3 fish • In most districts, smaller than average male fish caught, average female • Differences in selection among districts Nushagak Nushagak P = 0.057 P = 0.01 * * Ugashik P = 0.001 P = 0.47 Naknek-Kvichak * * Naknek-Kvichak P = 0.009 * * P = 0.083 Proportion frequency Proportion frequency Togiak P < 0.001 P = 0.273 * * Egegik P = 0.005 * * P = 0.52 Standardized selection differential Standardized selection differential

29. Average length of ocean age 3 fish has decreased over time • In most districts, fish getting smaller over time • Differences in size decline among districts 620 Nushagak slope=-0.60 Ugashik 620 slope=-0.16 slope=-0.64 slope: P < 0.001 520 Naknek-Kvichak slope=-0.26 slope=-0.16 slope: P = 0.041 Average length (mm) 520 Togiak 620 Average length (mm) slope=-0.19 slope: P = 0.172 slope=-0.05 Egegik 620 slope=-0.31 slope=-0.21 slope: P = 0.018 520 slope=-0.21 slope: P = 0.009 520

30. Vulnerability differs by length & sex example Males J. Carter Females

31. Vulnerability curves differ among years 2002 1980 1991 420 420 620 620 420 620 Length (mm) Females J. Carter J. Bennis