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Warmer water temps? Cod may not be too bothered

Researchers in Denmark have used sophisticated technology to determine the temperature threshold of cod fish. Presented in the Marine Ecology Progress Series, the findings are an outcome of the CODYSSEY ('Cod spatial dynamics and vertical movements in European waters and impli...

Researchers in Denmark have used sophisticated technology to determine the temperature threshold of cod fish. Presented in the Marine Ecology Progress Series, the findings are an outcome of the CODYSSEY ('Cod spatial dynamics and vertical movements in European waters and implications for fishery management') project, which was supported under the 'Quality of Life and management of living resources' programme of the EU's Fifth Framework Programme (FP5). Their findings suggest that warmer water is not as bad for adult cod as most people think. Cold water does not put a damper on cod. So if global warming is affecting everything on this planet, how are cod going to fare? Experts say this fish will have to rise to the challenge of meeting the escalating sea temperatures head on. Enter the CODYSSEY project partners, who investigated exactly at what temperatures cod are found in the Northeast Atlantic. Hundreds of cod were equipped with state-of-the-art mini thermometers to see just how hot the water has to be before they are adversely affected. Researchers from various European institutions, including the National Institute of Aquatic Resources in Denmark (DTU Aqua), placed advanced temperature gauges on more than 2,000 cod from various North Atlantic stocks, namely the Baltic and North Seas and the Skagerrak strait. According to the researchers, the gauges registered and stored water temperatures for more than 12 months around the fish at fixed regular intervals. The team has so far caught 902 cod through fishing, and has sent back the tags holding the stored data back to the lab. 'It's absolutely unique to have data from such a large and comprehensive study,' says Professor Ken Haste Andersen of DTU Aqua. Why cod and not some other fish? The researchers say two key features of cod helped their selection: it is an important fish commercially and its size is large enough to easily carry the electronic tag without it being a nuisance. 'Some fish were found at temperatures as cold as -1.5°C while others swam quite happily in water that was nearly 20°C above zero,' Professor Andersen notes. 'This shows that cod are relatively adaptable fish that can tolerate higher temperatures than was previously thought. However, while this is generally true for adult cod, they appear to be somewhat more conservative in their choice of water temperature when they spawn,' he adds. 'During this period, all the fish stocks studied consistently sought out water that had a temperature of between one and eight degrees°C. This indicates that the egg and larvae stages of a cod's life may constitute a particularly vulnerable time with regard to the effects of climate change.' It should be noted that while northeast Atlantic cod can survive in water temperatures that reach 20°C, there is no guarantee that all adult cod can tolerate all temperatures. For instance, transferring the cod from the North Sea to north of Iceland, with water temperature at -1.5°C would have an adverse impact on the fish. 'Each fish stock in each area is well-adapted to the local conditions,' Professor Andersen points out. 'It is widely known that cod can live in water at sub-zero temperatures, because they can produce antifreeze proteins which protect them.' By tagging the cod fish with data logging thermometers, scientists in Europe have a much better picture of how the fish will tolerate the ocean temperature hikes. Furthermore, the results of the CODYSSEY project are helping researchers better understand the horizontal and vertical movements of cod, and improve their predictions on the individual movements and seasonal distributions of cod stocks.For more information, please visit: CODYSSEY:http://www.codyssey.co.uk/Marine Ecology Progress Series:http://www.int-res.com/journals/meps/

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