Some Like It Hot

cod small Some Like It HotWarmer seas could mean more diverse fish schools in the northeast Atlantic Ocean. Rising water temperatures have already led to major shifts in the abundance of commercially important stocks, according to a new study that, for the first time, considers the absolute abundance of fish species and not just their presence or absence.

“We see many more southerly, warm-water species faring well on the European shelf than more northerly, cold-adapted species,” said Stephen Simpson of the University of Bristol in the United Kingdom, lead author of the Current Biology study. “This means more small-bodied, faster-growing species with shorter generation times, and potentially more diversity.”

Simpson’s team analyzed data coming from 11 independent surveys, covering 28 years, more than a million square kilometers of the European continental shelf, and more than 100 million fish. “Our study is the first to combine a whole suite of European data sets to get the ‘big picture’ of how warming is affecting fish communities,” Simpson said.

The northeast Atlantic has been described as the “cauldron of climate change,” with warming occurring at a rate four times the global average over the past 30 years, Simpson explained. “While a 1.31° Celsius change in mean annual temperature in the North Sea over the past three decades may sound trivial, temperature has a strong influence on egg maturation rates, growth, and survival of fish larvae, and impacts on the planktonic communities that underpin the food webs that sustain commercial fisheries,” he said.

Indeed, the data show that fish in European waters have undergone profound community-level changes that are related to dramatic warming trends for the region. The vast majority—a whopping 72 percent—of common fish species have already shown a response to the rising sea temperatures.

Of those, three out of every four fish species have grown in numbers with warming. Catches of cold-loving species, including haddock and cod, have dropped by half in the past three decades, while landings of warm-loving species, including hake and dab, have more than doubled.

The results show that studies focused only on changes to where particular fish species are found (species ranges) will miss the far more ecologically and economically relevant effects of warming, Simpson said. They also suggest that there will be an unavoidable change in what’s for dinner.

“We may see a further decline in cold-adapted species, many of which were the staple for our grandparents,” Simpson said. But now “exotic” warm water species could gain. “With effective management,” he says, “European seas have the potential to yield productive and sustainable fisheries into the future.”

Europe is currently considering major reforms in its fisheries policy, which has led to severe overfishing and damage to marine ecosystems.David Malakoff | September 15, 2011

Source: Steve Simpson, Simon Jennings, Mark Johnson, Julia Blanchard, Pieter-Jan Schön, David Sims and Martin Genner. “Continental Shelf-Wide Response of a Fish Assemblage to Rapid Warming of the Sea.” Current Biology doi:10.1016/j.cub.2011.08.0

Image © Greg Amptman | Dreamstime.com

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