Climate Change and Implications for Management of North Sea Cod ( Gadus morhua )

1. Climate Change and Implications for Management of North Sea Cod (Gadus morhua) L.T. Kell, G.M. Pilling and C.M. O’Brien CEFAS, Lowestoft

2. Acknowledgements This paper was prepared with funding support provided by the Commission of the European Communities Directorate General for Fisheries (DG XIV) and by the Department for Food, Environment and Rural Affairs (UK).

3. Objectives • Evaluate whether management strategies for North Sea cod i.e. • Recovery plans • Harvest Control Rules are robust to plausible hypotheses about climate change • Whether climate change is the most important factor for management

4. Methodology ~ Simulation IWC, MATACS/MATES • Experimental approach using computer simulation. • Operating Model • Hypotheses about Stock and Fishery dynamics • Management Procedure • Alternative Assessment and management options • Experimental treatments correspond to hypotheses about dynamics • Can includes a wide range of uncertainty

5. Uncertainty Sources of uncertainty implicitly considered • Process Error • Recruitment, somatic growth, natural mortality • Measurement Error • Occurs when collecting observations from a population • Estimation Error • Arises during the assessment process • Model Error • Models used within assessment procedures will never capture the true complexity of the dynamics • Implementation Error • Management actions are never implemented perfectly

6. Climate Change Hypotheses Climate change acts through temperature on • Growth (weight-at-age): • Optimum temperature for growth • Stock Recruitment Relationship • Juvenile survival • Carrying capacity

7. Temperature scenarios

8. Weight-at-age ~ f(T) Age 3 Age 5 Impacts on selectivity by gear, discarding practice and SSB

9. Stock Recruitment ~ Ricker 500000 450000 400000 350000 300000 Recruitment 250000 200000 150000 100000 Biomass at maximum recruitment 50000 0 0 200000 400000 600000 800000 1000000 1200000 1400000 SSB 2001

10. Stock Recruitment ~ a(T) 500000 450000 400000 350000 300000 Recruitment 250000 200000 150000 100000 Biomass at maximum recruitment 50000 0 0 200000 400000 600000 800000 1000000 1200000 1400000 SSB 2001 Hadley Low 2030

11. Stock Recruitment ~ a(T) 500000 450000 400000 350000 300000 Recruitment 250000 200000 150000 100000 Biomass at maximum recruitment 50000 0 0 200000 400000 600000 800000 1000000 1200000 1400000 SSB 2001 Hadley Low 2030 Const. Increase 2030

12. Stock Recruitment ~ a(T) R/S at origin 500000 450000 400000 350000 300000 Recruitment 250000 200000 150000 100000 50000 0 0 200000 400000 600000 800000 1000000 1200000 1400000 SSB 2001 Hadley Low 2030 Const. Increase 2030

13. 500000 450000 400000 350000 300000 250000 200000 150000 100000 50000 0 0 200000 400000 600000 800000 1000000 Stock Recruitment ~ b(T) Recruitment 1200000 1400000 SSB 2001 Hadley Low 2030 Const. Increase 2030

14. Productivity Curve • ~ Juvenile Survival Affects fishing mortality Reference points (FMSY, FCrash)

15. Productivity Curve • ~ Carrying Capacity Affects biomass reference points (BMSY, Blim, BPA) • ~ Juvenile Survival Affects fishing mortality Reference points (FMSY, FCrash)

16. Management Strategies Strategies investigated were either those adopted by the European Commission or currently under consideration by the Commission • Short-term • Recovery plans • Long-term • Harvest Control Rules

17. Short-term Management Strategies • North Sea cod Recovery Plan (Adopted in December 2003) • Set Catch each year so that SSB increases by 30% annually until stock recovers to 150,000 t (BPA)

18. Results • Predicated upon the assumptions used in the simulation experiments • Don’t allow us to predict what will happen • Allow us to investigate the relative importance of the various processes and the interactions between them

19. Recovery ~ Climate Change

20. Recovery ~ Climate Change Most of the biomass during the recovery period is from year-classes recruited prior to implementation of the recovery plan

21. Recovery ~ Yields

22. Recovery ~ Climate Change

23. Recovery ~ In a mixed fishery?

24. Recovery ~ But will we know? 1.0 2001 Low ~ Alpha Probability of Recovery High ~ Alpha 0.5 Low ~ Beta High ~ Beta Cod Bycatch Perceived 0.0 2000 2005 2010 2015 Year

25. Long-term Management Strategies • Harvest Control Rules where Total Allowable Catches (TACs) are set for a target Fishing Mortality • Target F = 0.65 (FPA defined by ICES) • Target F = 0.45 • ICES HCR • F reduced if SSB < BPA F F = 0.65 SSB BPA

26. Management Objectives • Sustainability • SSB > BPA (SSB at which spawning impaired) • Yields • Stability of Yields (long-term planning)

27. Harvest Control Rules ~ Results

28. Results • Yields of North Sea cod at the levels seen in the 1980’s could be achieved if fishing mortality reduced and fisheries managed on a mixed stock basis

29. Conclusions I • Climate Change has little effect in short-term • Management of fleets in the mixed North Sea fisheries more important, especially if distribution of stocks change • Can not easily estimate changes in MSY or BMSY • As important to understand the mechanism through which climate change acts as well as to quantify the magnitude of change • Unlikely to determine this solely through stock assessment or analyses based upon VPA

30. Conclusions II • Do not try to make Stock Assessment more complex by including environmental covariates • Develop simpler management procedures that meet management objectives and are robust to uncertainty about the true dynamics • Do this by evaluating candidate strategies against plausible hypotheses about ecological, environmental, fishery processes and the interactions between these processes