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Comments and developments on extended single-species and minimally realistic models

Comments and developments on extended single-species and minimally realistic models. James N. Ianelli Alaska Fisheries Science Center Seattle, WA.

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Comments and developments on extended single-species and minimally realistic models

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  1. Comments and developments on extended single-species and minimally realistic models James N. Ianelli Alaska Fisheries Science Center Seattle, WA This information is distributed solely for the purpose of predissemination peer review under applicable guidelines. It has not been formally disseminated by NOAA Fisheries and should not be construed to represent any agency determination or policy.

  2. Age-structured models used at the AFSC

  3. Predators as “fleets” approach… Hollowed, A.B., Ianelli, J.N., and Livingston, P.A. 2000. Including predation mortality in stock assessments: a case study for Gulf of Alaska walleye pollock. ICES J. Mar. Sci. 57: 279–293.

  4. Extended single species models Case study of Eastern Bering Sea Pollock: impact of environmental/ecosystem variability on management advice

  5. Translation: the higher the variance, the lower the upper limit on TAC Tactics from our management guidelines… Formally risk averse

  6. Some sources of error in Fmsy Natural mortality Growth Stock-recruitment relationship: Selectivity

  7. How does SRR affect EBS pollock management? • Directly by adjusting the maximum permissible harvest level • TAC level would be considerably higher under the following Fixed selectivity Deterministic mean-mass-at-age Fixed natural mortality

  8. Characterizing cannibalism Prey length Month Prey sizes Predator concentrations 10 Studies linking water column data to predator-prey overlap so far inconclusive

  9. Regimes?

  10. Recruitment responses to putative regimes relatively weak for pollock 1977-1988 1977-1998 1977-2004 Mean 1989-2004 Recent history Early period

  11. Body-weight loss/gain Based on average for males E of 170W, 1991-2006

  12. Impact on management due to growth changes are important

  13. Adding uncertainty in future mean mass-at-age affects quota limit Adding future mass-at-ageuncertainty lower the TAC by >20,000 t

  14. Retrospective diagnostics Balloons proportional to uncertainty

  15. MSM • Starts w/ age-structured assessment model • Same fisheries and survey data, some structural simplifications • Diet data incorporated • Easy evaluation of alternative predator functional responses • Coded in C++ (ADMB) • Ease of estimation and evaluating uncertainty (MCMC, non-linear mixed-effects approaches) Incomplete data are ok!

  16. Schematic changes where k = prey species a = prey age y = year f = fishery r = predator species u = predator age From Kinzey

  17. Predator functional responses • Type I: linear • Type II: asymptotic • Type III: S-shaped • Type IV: ratio interference • Type V: ratio pre-emption, asymptotic • Type VI: Hassel-Varley • Type VII: “Ecosim” Predation mortality is allowed to vary among predator age-classes to better mimic the ration data. From Kinzey

  18. Data vs model fit:daily ration (Types I - VII) From Kinzey

  19. Model communication

  20. Pollock

  21. Age-1 pollock predation

  22. Resource utilization

  23. Age-1 pollock predation

  24. Conclusions • Extended single species models • Implied affects on quota limits exist • Direct affect on quota limits work • MSM • Allow focus on prey sizes and tailored suitabilities • Provides ability for statistical evaluation Fit to real “Data” • Can be adapted to encompass alternative functional responses • Are limited in scope • Only a few elements of the ecosystem included

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