4Cod StocksCod presently inhabit many of the continental shelf areas of the northern North Atlantic, bordering the subpolar gyre.
5Cod Recruitment and Temperature Warm Temperaturesincreases RecruitmentWarm Temperaturesdecreases Recruitment76849Recruits103TempMean Annual Bottom Temperature112Planque and Fredou (1999)
6Growth RatesTemperature accounts for most of the differences in growth rates between stocks (Brander 1994, 1995).
7Temperature accounts not only for stock differences but also for interannual variability within stocksWest GreenlandFaroe IslandsBrander 1995
8Field estimate of growth rate Specific growth rates from Brander (2003).
9Further 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.
10From Rätz and Lloret 2003The condition of the fish as measured by Fulton’s K (higher values means better condition) also shows an increase with increasing temperature.
11Temperature appears to affect age of maturity of Atlantic Cod 777663.52
12Combining age of maturity of different cod stocks from Hutchings and Myers (1993) with bottom temperatures from Brander (1994).
14Future changes in global mean temperature for six different emission scenarios using several different climate models (IPCC; 200 ).
15The 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
16Summary 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).
18Cod Recruitment and Temperature Warm Temperaturesincreases RecruitmentWarm Temperaturesdecreases Recruitment76849Recruits103TempMean Annual Bottom Temperature112Planque and Fredou (1999)
19GBIf BT < 5° and T warms stock recruitment generally increaseIf BT between 5° and 8.5°C little change in recruitmentIf BT >8.5°C recruitment generally decreasesIf BT 12°C we do not see any cod stocks
20Effect on abundance of 1°C increase No changeDecreaseCollapse?
26Growth – 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.
27Summary 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.
28Caveats 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 .
29Observational 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.