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 God Ø 2002 Bulletin of Marine Science)

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

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 Bristol Bay Upper Cook Inlet

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 Females Males

12. Vulnerability profiles by length Females Males 1990 19941999 20022003 400 650 400 650 400 650 0 1 0 1

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

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

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 Proportion frequency Standardized selection differential P < 0.001 P = 0.143 P < 0.001 P = 0.002 P < 0.001 P = 0.051 P = 0.010 P = 0.756 Nushagak Naknek-Kvichak Egegik Ugashik Togiak Nushagak Naknek-Kvichak

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

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

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

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

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

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

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

25.  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. BennisJ. Carter Future work J. Bennis

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

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

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

31. Females Vulnerability curves differ among years J. Bennis Length (mm) 19801991 2002 420 620 420 620 420 620 J. Carter