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

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Presentation on theme: "1 1 Ken Drinkwater Institute of Marine Research, Bergen, Norway Bjerkenes Center Climate Research The Response of Atlantic Cod (Gadus morhua) to Future."— Presentation transcript:

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

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

3 3 3 Temperature-Cod Relationships

4 4 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 Mean Annual Bottom Temperature Temp Warm Temperatures decreases Recruitment Warm Temperatures increases Recruitment Recruits Planque and Fredou (1999)

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

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

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

9 9 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 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 Cod 6

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

13 13 Future Climate Change

14 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 16 Summary of Temperature Changes in Cod Regions Predicted temperature changes range from 2° to 5°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). Multi-model variability varies from ±1.5°C at lower values to ±3°C.

17 17 Cod Responses to Temperature Scenarios

18 Cod Recruitment and Temperature Mean Annual Bottom Temperature Temp Warm Temperatures decreases Recruitment Warm Temperatures increases Recruitment Recruits Planque and Fredou (1999)

19 19 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 GB

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

21 2°C Temperature Increase

22 3°C Temperature Increase

23 4°C Temperature Increase

24 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 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 27 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. Summary

28 28 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. Caveats

29 29 In spite of the uncertainties and general nature of the results, there is support for the conclusions. 1.During the 1920s and 1930s warming, cod spread northward (see Drinkwater poster). 2.There is evidence that spawning sites move northward under warming conditions (see Sundby and Nokken poster). 3.Cod production and biomass was high in most regions during the last warm period from the 1920s to the 1960s or so. Observational Support for Conclusions

30 30 From Rätz and Lloret 2003

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