1. The Response of Atlantic Cod (Gadus morhua) to Future Climate Change
Ken Drinkwater
Institute of Marine Research, Bergen, Norway
Bjerkenes Center Climate Research

2. Presentation focuses upon temperature effects and uses what we know from past studies to predict the future
Outline
Temperature-Cod Relationships
Future Climate Change
Predicted Cod Responses

3. Temperature-Cod Relationships

4. Cod Stocks
Cod presently inhabit many of the continental shelf areas of the northern North Atlantic, bordering the subpolar gyre.

5. Cod Recruitment and Temperature
Warm Temperatures
increases Recruitment
Warm Temperatures
decreases Recruitment 7 6 8 4 9
Recruits 10 3
Temp
Mean Annual Bottom Temperature 11 2
Planque and Fredou (1999)

6. Growth Rates
Temperature accounts for most of the differences in growth rates between stocks (Brander 1994, 1995).

7. Temperature accounts not only for stock differences but also for interannual variability within stocks
West Greenland
Faroe Islands
Brander 1995

8. Field estimate of growth rate
Specific growth rates from Brander (2003).

9. Further on Temperature Effects
Individual growth and production of Atlantic cod is found to increase with temperature (Dutil and Brander, 2004).
In spite of this, population abundance tends to be maximum in colder water stocks, e.g. Northeast Arctic cod and until recently, Northern cod off Newfoundland.
There are no cod stocks found at average bottom temperatures exceeding 12°C.

10. From Rätz and Lloret 2003
The condition of the fish as measured by Fulton’s K (higher values means better condition) also shows an increase with increasing temperature.

11. Temperature appears to affect age of maturity of Atlantic Cod7 7 7 6 6
3.5 2

12. Combining age of maturity of different cod stocks from Hutchings and Myers (1993) with bottom temperatures from Brander (1994).

13. Future Climate Change

14. Future changes in global mean temperature for six different emission scenarios using several different climate models (IPCC; 200 ).

15. The multi-model ensemble annual mean change of the temperature (color shading), its range (thin blue isolines) (°C) and the multi-model mean change divided by the multi-model standard deviation (solid green isolines, absolute values) for relative to

16. Summary of Temperature Changes in Cod Regions
Predicted temperature changes range from 2° to 5°C.
Multi-model variability varies from ±1.5°C at lower values to ±3°C.
Maximum temperatures and uncertainty ranges in the north (e.g. Barents Sea, Greenland) and minimum in the south (e.g. North Sea, Celtic Sea, Georges Bank).

17. Cod Responses to Temperature Scenarios

18. Cod Recruitment and Temperature
Warm Temperatures
increases Recruitment
Warm Temperatures
decreases Recruitment 7 6 8 4 9
Recruits 10 3
Temp
Mean Annual Bottom Temperature 11 2
Planque and Fredou (1999)

19. GB
If BT < 5° and T warms stock recruitment generally increase
If BT between 5° and 8.5°C little change in recruitment
If BT >8.5°C recruitment generally decreases
If BT 12°C we do not see any cod stocks

20. Effect on abundance of 1°C increase
No change
Decrease
Collapse ?

21. 2°C Temperature Increase

22. 3°C Temperature Increase

23. 4°C Temperature Increase

24. Northward Expansion
In addition to the changes in the present stocks, under warming temperatures the cod with expand northward. This will include establishing new spawning sites.
How far north?

25. ?
Northward Expansion

26. Growth – With increasing temperatures both individual growth (Brander 1995) and stock production (Dutil and Brander 2003) should generally increase.
Condition – With increasing temperatures and improved growth rates the cod should be in better condition.
Maturity – With increasing temperatures age of maturity will likely decrease.

27. Summary With increasing temperatures:
Overall Atlantic cod production should generally increase both due to individual growth and stock production and better condition.
The cod will expand northward, which will include the establishment of new spawning grounds.
However, we expect some of the present warmer water stocks will decrease substantially and the stocks in the warmest waters may disappear altogether.

28. Caveats Only considered temperature effects on cod.
The temperature changes will be linked to what happens to the circulation changes, e.g. to the thermohaline circulation and wind forcing.
There is high uncertainty in the future temperature scenarios and few regional climate models are available.
Cod is not independent of the ecosystem and can not be considered separately, i.e. its food.
Fishing will play a major role in the response and must be included in future .

29. Observational Support for Conclusions
In spite of the uncertainties and general nature of the results, there is support for the conclusions.
During the 1920s and 1930s warming, cod spread northward (see Drinkwater poster).
There is evidence that spawning sites move northward under warming conditions (see Sundby and Nokken poster).
Cod production and biomass was high in most regions during the last warm period from the 1920s to the 1960s or so.

30. From Rätz and Lloret 2003