Wednesday, June 5, 2013

Study Looks at Fisheries Reshaped by Warming Oceans

A study by University of British Columbia scientists shows that ocean warming has had a global impact on the mix of species caught by fishermen, replacing some of those traditionally caught in many fisheries worldwide at least since 1970.

Previous studies indicated some species are shifting location in response to temperature increases, with fish gradually moving away from the equator into cooler waters.

UBC’s William Cheung and his co-authors used the temperature preferences of fish caught around the world to determine the relationship between fisheries catch and ocean warming. They first assembled data on the distribution of 990 marine fish and invertebrates, when assigned each species a temperature preference based on the average sea surface temperature in areas where that species was predicted to have occurred between 1970 and 2000.

Then to measure changes in the composition of marine fisheries, the researchers compiled data on the tonnage of each species caught in the 52 marine ecosystems that account for most of the world’s fisheries. Next, for each ecosystem and each year from 1970 through 2006, they calculated the average temperature preference of the species, weighted by the amount caught. Finally, the researchers determined the connection between ocean warming and changes in fisheries catch by using a statistical model that separates out other factors, such as fishing effort and oceanographic variability.

A summary provided through the PEW Charitable Trusts said the authors found that, except in the tropics, catch composition in most ecosystems slowly changed to include more warm-water species and fewer cool-water species.

Earlier research led by Cheung predicted continuing changes in fish distribution and catch as oceans warm. These shifts could have several negative effects, which may be felt most in the tropics, where water temperatures could exceed the preferences of many tropical species, resulting in a large reduction in catch.

Additional impacts could include loss of traditional fisheries, decreases in profits and jobs, conflicts over new fisheries that emerge cause of distribution shifts, and food security concerns, particularly in developing countries. The research was published in May in the periodical Nature.

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