Multispecies Production Models:Past and Present, Examples at the NEFSC

1. Multispecies Production Models:Past and Present, Examples at the NEFSC By W.J. Overholtz, J.S. Link, H. Moustahfid, R.J. Gamble, M.C. Tyrrell, B.E. Smith NEMOW-August 2007

2. 2-Tier Surplus Production Analysis • Brown et al 1977: analysis of the ICNAF bottom trawl fishery in SA 5+6 during 1961-1972. • Mayo et al 1992: re-analysis with additional years from 1973-1987. • Aggregate catch and effort data to estimate surplus production and BRPs.

3. Brown et al. 1976 Catch and Effort 1961-1972 Aggregate MSY 900,000 mt Summed Quota 1,300,000 mt

4. Mayo et al. 1992- Catch and Effort 1960-1987 1960-1976 Aggregate MSY 700,000 mt 1977-1987

5. Conclusions • “…summing the MSYs from individual assessments may be an overestimate of the total MSY.” • The 2nd Tier Quota was 30-45% lower than the sum of the individual quotas (1.3 e6 mt). • Similar results from LP analyses: weak stock management necessary!

6. Gulf of Maine-Georges Bank Herring Surplus Production Accounting for Predation

7. Atlantic Herring M2 and F during 1959-2002

8. Modified Fox model

9. If predators increase, less fishery SP would be available At Bmsy=1452 kt

10. Predator vs Fishery Tradeoff 2007 1200 2026 1400 At Bmsy=1452 kt

11. Conclusions • Predation mortality (M2) should be included in stock assessments of prey fish. • SS assessments of prey fish are generally optimistic relative to BRPs • If the fishery and predators utilize the same size spectrum of prey, then tradeoffs are probably warranted.

12. Guild-Based Biomass Production Model • We examined a suite of ecological and harvest scenarios. • The ecological scenarios: modify competition and predation parameters (nsh). • The harvest scenarios: modifying harvest rates. • The goal was to investigate general properties and responses in a Guild System

13. Modified Schaefer Model N =Biomass B = Competition Coefficient I = species R = Growth Rate a = Predation Coefficient p = predator (on species i) H = Harvest Rate K = Carrying Capacity g = Guild Member G = Guild

14. DEMERSALS OVERFISHED 1. total system biomass increased. 2. Piscivores and Shrimp-Fish declined. 3. Planktivores increased and k increased for this guild. 4. Benthivores increased due to a higher growth rate, and a reduction in competition and predation. 5. Reduction in predation caused an overall biomass increase.

15. PISCIVORES OVERFISHED 1. Total biomass of the system increased, 2. Rankings within the Planktivore guild changed. This was because more predation occurred on PL1 and PL2 than PL4. 3. When predation effects were lowered, PL1 and PL2 were able to out compete PL4.

16. Results for this scenario show a strong similarity to the historical situation in the Northeast U,S, Atlantic Ecosystem . Starting in the early 1990’s, the Piscivore biomass began to decline, resulting in an increase in Planktivore biomass. Additionally, increasing trends in Benthivore and Shrimp-amphipod biomasses occur in both the real world situation and this scenario.

17. PELAGICS OVERFISHED 1. Total biomass of the system decreased. 2. Most of this decrease can be attributed to the much lower biomass of Planktivores.

18. CONCLUSIONS 1. Predation appears to be the dominant biotic term within the model. 2. Overall biomass of a guild tends to be stable. even though individual species biomasses may change greatly. 3. Changes in one biotic factor may cause unexpected results due to predatory and competitive interactions. 4. A demonstration copy can be obtained by contacting Robert Gamble (Robert.Gamble@noaa.gov).

19. General Conclusions • Rich History of Past and Current Use. • Sum and Parts are Important • Addresses the Issue of Biological and Technological Interactions • Could this Approach to Simplify Management.