In rapidly warming seas, some fish lose while others gain

(Press-News.org) Rising temperatures in the northeast Atlantic Ocean have already led to major shifts in the abundance of commercially important fish stocks. That's according to a report published online on September 15 in Current Biology, a Cell Press publication, that is the first to consider the absolute abundance of species as opposed to their presence or absence alone.

"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. "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. "The flip side is a likely increase in species that for the UK may seem relatively exotic now—red mullet and John dory. Over time, with effective management and an appropriate response in consumer demand, European seas have the potential to yield productive and sustainable fisheries into the future."

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