1. A multi-species population assessment model for the Gulf of Alaska Kray F. Van Kirk, SFOS, UAF, Juneau Terrance J. Quinn II, SFOS, UAF, Juneau Jeremy S. Collie, GSO, URI, Narragansett ftkv@uaf.edu@uaf.edu

2. Jointly funded by AK and RI Sea Grant Jointly funded by AK and RI Sea Grant Also collaboration with North Sea colleagues: Lewy, Vinther (Denmark) Also collaboration with North Sea colleagues: Lewy, Vinther (Denmark) Project started February, 2004 Project started February, 2004 Species groups Species groups Gulf of Alaska Gulf of Alaska Georges Bank Georges Bank North Sea North Sea Sea Grant

3. Justification Crisis in Fisheries Management Crisis in Fisheries Management Single species analysis does not answer questions of multi-species interactions Single species analysis does not answer questions of multi-species interactions Ecosystem approaches desired Ecosystem approaches desired Natural mortality is not constant! Natural mortality is not constant! Harvest strategies cannot evolve until models do Harvest strategies cannot evolve until models do

4. Previous MSVPA Models Predation mortality estimated from gut studies Predation mortality estimated from gut studies Single predation coefficient Single predation coefficient Works backwards from oldest ages Works backwards from oldest ages Catch-at-age is measured without error Catch-at-age is measured without error Applied to North, Baltic and Bering Seas, Georges Bank, and a few tropical areas Applied to North, Baltic and Bering Seas, Georges Bank, and a few tropical areas

5. Model Overview Catch-age measured with error Catch-age measured with error Forward time progression from Forward time progression from age 1 recruitment Cohort abundance subject to fishing, Cohort abundance subject to fishing, flexible predation, and residual natural mortality

6. Age-structured Analysis

7. Modeling Predation Mortality Annual Ingestion of Predator Age (grams) = consumption of modeled prey of interest + consumption of non-modeled ‘other food’. Where annual ingestion rate is given by: Growth Increment Growth Efficiency Hall et al. in press

8. Components of Modeled Prey (1) Predator j of size b preference for prey of size a. (from Ursin 1971, where size-preference is a function of predator-prey weight-at-age ratio) (from Ursin 1971, where size-preference is a function of predator-prey weight-at-age ratio) Predator j preference for prey of species i. (from AFSC data, as a ratio of prey i consumed relative to total prey consumed; changes over time) (from AFSC data, as a ratio of prey i consumed relative to total prey consumed; changes over time)

9. Components of Modeled Prey (2) Suitability of prey i,a to predator j,b : size/age preference * prey preference Availability of prey i,a to predator j,b : prey suitability * prey abundance

10. Total Annual Consumption Consumption of prey i,a by predator j,b Prey Availability Predator Abundance Predator Ingestion Total Available Food (Modeled Prey And Other Food)

11. Total Available Food T.A.F. = Modeled prey + all other prey How to quantify ‘other prey’? - Very little data Use factor to multiply modeled prey (10x, 50x…) to obtain estimated biomass of Other Prey Set multiplier as parameter to be estimated Modeled prey, species iAll other prey

12. Total ‘P’ for prey i,a by predator j Predation Mortality ‘P’ Sum of ALL predation on species i age a by ALL ages of predator j Total predation on species i,a (grams) Total biomass of species i,a (grams)

13. Cohort Abundance Residual Natural Mortality Fishing Mortality Predation Mortality Traditional Natural Mortality ‘M’

14. Initial Model Set-up Pacific Cod (Gadus macrocephalus) Arrowtooth Flounder (Atheresthes stomias) Walleye Pollock (Theragra chalcogramma)

15. Initialization Parameters Abundance at age for year 1(SAFE) Abundance at age for year 1(SAFE) Fixed overall F (Mean 1981 – 2001) Fixed overall F (Mean 1981 – 2001) Fixed R (0.1) Fixed R (0.1) Spawner-Recruit alpha and beta Spawner-Recruit alpha and beta Prey Preference (Mean 1981 – 2001) Prey Preference (Mean 1981 – 2001)

16. Changes in Prey Preference

17. Population Trends (SAFE) Arrowtooth Flounder Walleye Pollock Pacific Cod

18. Initial Results  Fishing pressure on pollock too great  Insufficient food available to pollock Arrowtooth Flounder Pacific Cod Walleye Pollock

19. Increase ‘Other Food’ factor from 10x to 50x Walleye Pollock Arrowtooth Flounder Pacific Cod BASE CASE SCENARIO

20. Predation Mortality from Base Case Pollock Cod ATF

21. Full Recruitment ‘F’ for pollock at 1 Pollock Cod ATF Cod Predation on ATF 1981 – 2001 Base Case Predation on ATF 1981 – 2001 F = 1

22. Full Recruitment ‘F’ for pollock at 1 Other Food factor = 50xOther Food factor = 100x

23. Full Recruitment ‘F’ for pollock at 0 Pollock Cod ATF Pollock ATF Cod Predation on Pollock 1981-2001: Base CasePredation on Pollock 1981-2001: F = 0 Pollock

24. Full Recruitment ‘F’ for pollock at 0 Predation on ATF 1981-2001: F = 0 Predation on ATF 1981 – 2001 Base Case Pollock Cod ATF

25. Model Sensitivities Prey Abundance Prey Abundance Predator Abundance Predator Abundance Prey preference and ‘Other Food’ factor Prey preference and ‘Other Food’ factor Fishing Pressure Fishing Pressure

26. Next Steps Parameter Estimation Parameter Estimation Rho (species preference) Rho (species preference) Elements of size-preference function Elements of size-preference function ‘Other food’ multiplier ‘Other food’ multiplier Objective Functions Objective Functions Fishery catch at age Fishery catch at age Survey catch at age Survey catch at age Stomach contents (predation rates) Stomach contents (predation rates) Addition of Pacific halibut and Steller Sea Lion Addition of Pacific halibut and Steller Sea Lion

27. Areas for Exploration Predation between age classes and connection with fishing pressure Predation between age classes and connection with fishing pressure Complexity of multi-species model vs. robustness of single species models Complexity of multi-species model vs. robustness of single species models Estimation of recruitment parameters once other parameters are set Estimation of recruitment parameters once other parameters are set