1. Evaluation of a North Sea Cod recovery plan taking into account biological interactions (Alexander Kempf, Morten Vinther, Jens Floeter, Axel Temming)

2. Introduction

3. Cod stock in the North sea is in serious problems: - SSB is on a historical all time low well under B lim - very low recruitment numbers in the last years

4. In recent years management measures have been applied to rebuild the cod stock: - box closures - effort reductions - cut down of total allowable catch (TAC) Latest proposal of European comission (Reg 2003/0090 (SNS)): - effort reductions/ control - Harvest Control Rules (HCR) for setting TAC

5. HCR rules for rebuilding cod stock (Article 6 and 7 of Reg 2003/0090 (SNS)): a) If SSB is over B lim 1.Council decide by qualified majority on a TAC for the following year 2.Either the SSB reaches B pa or SSB should increase by 30% per year 3.Fishing mortality F is not allowed to exceed F pa (F pa for Cod in the North Sea = 0.65) 4.If SSB is predicted to exceed B pa with rule number two, a TAC should be calculated that will lead to a SSB equal to B pa 5.Except for the first year, the TAC is not allowed to increase or decrease by more than 15% compared to the TAC one year before 6.4. + 5. shall not apply, if F pa (see 3.) would be exceeded!

6. b)If SSB is under B lim : 1.If SSB is predicted to be under B lim in the end of the year, the fishing mortality (F) should be reduced to a level, that SSB will pass B lim in the following year. 2.If fishing mortality must be reduced to a level, that the resulting TAC would be less then 20% of past years TAC, the fishing mortality must be increased that the resulting TAC is exactly 20% of past years TAC.

7. Questions to be adressed in the analysis carried out: -can the mentioned HCR rules help cod to recover? - what are the effects of a cod recovery on other species in a multispecies context? - lead the allowance of biological interactions to other answers for the fisheries management than the usual single species assessment?

8. Material and Methods

9. Article 6 and 7 in pseudo computer language: (based on Morthen Vinther)

10. Theory of VPA: VPA (Virtual Population analysis): Rather simple technique by which you back-calculate how many fish there must have been in the sea to account for the observed catches (virtual population) (Sparre 1983). Cohort concept: C= numbers caught by fishing D= number of natural deaths N= stock numbers

11. Theory of VPA: Two kinds of VPA´s: SSVPA: no biological interactions are taken into account (e.g. predation mortalitiy)!  only a qualified guess for the coefficient of natural mortalitiy (M)  M is constant over the hole calculation time period  Z= F + M MSVPA: predation mortality (M2) is quantified inside the model!  Z= F+ M2+ M1 Z = total mortality F = fishing mortality M2= predation mortality M1= residual natural mortality (starvation, diseases...)

12. VPA run with 4M (multi or single species) inital stock numbers stock recruitment relationship F in the first prediction year suitabilities for calculation of M2 Multi and single species VPA keyrun of year 2003 was used! Make prediction for one year i using 4M Take output from 4M and apply HCR routines for estimating next years fishing mortality F (R program) Write input data for 4M prediction Final prediction year? END yes no Predictions using 4M (single and multi-species possible) as external procedure: (based on Morthen Vinther) i= i+1

13. Further notes on prediction runs: - HCR rules were simulated to be in use from year 2003 on - last prediction year was 2010 - included predator and prey species: only predatorpredator and preyonly prey saithecodherring North Sea mackerelwhitingsprat western mackerelhaddockN. pout sea birdssandeel raja radiata. grey seals horse mackerel

14. - Stock recruitment relationship: - Reference point (B lim, B pa etc.) adjustment for using single species reference points in a multi species assessment Recruitment (Ricker relation or Arithmetic Mean) SpeciesRecruitmentOmitted Years CodRicker1969 HaddockAM WhitingRicker1977-1980 SaitheRicker HerringRicker SpratRicker1973 and 1975 SandeelAM Norway PoutAM SoleRicker PlaiceRicker

15. Way of reference point adjustment: ( based on Morthen Vinther ) Stock areas in single species and multispecies assessment differ:  Single species values for B pa and B lim were reduced by the same percentage as catches from outside area IV contribute to the total catch.  F pa was left unchanged single speciesmulti species North Sea (IV) Kattegat and Skagerrak (III) English Channel (VIId) only North Sea (IV)

16. Simulation szenarios carried out among others (in total 17): Szenario no. HCR applied to species single or multi species mode Prediction value for F 1 nonesingleF current, SSVPA 2 nonemulti F current, MSVPA 3 nonesingleF pa 4 nonemultiF pa 5 Codsingle F current, HCR 6 CodmultiF current, HCR 7 Cod, Whiting, Haddock multiF current, HCR

17. Results

18. HaddockSandeel Cod Whiting Scenario with F curr and no HCR species:

19. CodWhiting HaddockSandeel Scenario with F pa and no HCR species:

20. Scenario with F curr and Cod as HCR species: Cod Whiting Haddock Sandeel

21. Scenario with F curr and Cod, Whiting and Haddock as HCR species: Cod Whiting HaddockSandeel

22. Summary and discussion: 1. There are marked differences between single species and multi species assessment. Reasons: - SSVPA and MSVPA calculate different F pattern stock recruitment relationships. Single species assessment can´t cover trends in predation mortality due to increasing or decreasing predator stocks!

23. Summary and discussion: 2. Cod recovery has negative effects on other species when taking biological interactions into account (esp. whiting)  Recovery plans must include strategies for all species of economic and ecological interest not only for one single species alone! 3.HCR seem to help cod to recover But: In keyrun 2003 Grey gurnard was excluded!

24. Grey gurnard plays an important role: - in keyrun 2002 actual responsible for about 60% of the predation mortality on young cod - in keyrun 2003 excluded from the model Reason: Cod can´t recover in the model through the high predation mortality caused by grey gurnard even if cod is fished with F pa !

25. Questions: 1.Only one stomach data set from 1991 available  just an extreme situation was sampled?  overlap highly variable  actual MSVPA set up ignore this! 2. Is the bad situation for cod caused by the Holling type II parameterisation?

26. Final conclusions: When thinking about recovery plans and HCR, biological interactions must be taken into account! But: Uncertainties in multi species modelling must be reduced to give certain and useful answers!  EU project BECAUSE try to solve these problems Website: www.rrz.uni-hamburg.de/BECAUSEwww.rrz.uni-hamburg.de/BECAUSE

27. Thanks for your attention!