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Warmer Barents Sea could spell disaster for cod, haddock

Warmer temperatures could decimate many important fisheries, according to the Institute of Marine Research.

The temperature of the Barents Sea could increase by nine degrees Celsius by the end of the century, if no action is taken to curb greenhouse gas emissions. And that could spell doom for many important fisheries, like cod and haddock.

These are the findings of a recent report from Norway’s Institute of Marine Research, which used temperature projections from the latest Intergovernmental Panel on Climate Change (IPCC) report.

Under the IPCC’s business-as-usual scenario, average global temperature will increase by up to 4.5 degrees Celsius. Temperature increases in the Arctic are predicted to be double the global average, in part because the ice sheet across much of the Arctic is quite thin. As it melts, the darker surfaces of land and water absorb more heat and further accelerate warming.

Svein Sundby, the research scientist who wrote the report, said an increase of nine degrees could make the Barents Sea unlivable for many fish populations.

“That is absolutely over the hill for cod and many other boreal species,” he said. “Most of the Norwegian commercial species are boreal species.”

Sundby said Atlantic cod on the Norwegian continental shelf thrive in ocean temperatures between zero and 11 degrees Celsius. The Barents Sea is currently about four degrees. At 13 degrees, cod eggs and larvae would struggle to survive.

Barents Sea still below the “optimal temperature”

Warmer waters aren’t always harmful to fish species, depending on the amount of the increase and the baseline temperature. To date, rising sea surface temperatures have actually improved Barents Sea fisheries. The report said the sea has warmed by 0.8 degrees since the early 1980s, which has increased numbers of many stocks, including cod, haddock, herring, and mackerel.

But Sundby said further south, that same temperature increase has had a negative effect on fisheries, because temperatures there were already approaching the limit for boreal species.

“There is an optimal temperature for Atlantic cod, and the Barents Sea at this stage hasn’t reached the optimal temperature yet,” he said.

If the Barents Sea were to experience rapid warming, Sundby said it’s possible southern fish stocks would move further north to replace the declining northern populations. But that’s not a guarantee, due to the “specialized” conditions in the high North.

Many unknowns

The long, dark winters in the Barents Sea affect the life cycle of plankton, which form the base of the food chain. Plankton accumulate large fat stores in the summer months, and then spend the winters in a type of hibernation in the cold, deep waters. Fish species that feed on plankton in the Barents Sea are adapted to this unique behaviour, but Sundby said there’s no guarantee that fish populations from further south would adjust to these conditions.

“That’s a very special kind of life cycle,” he said. “If the temperate species are not able to adapt to do the same… they will not survive in the Barents Sea, even if the temperature is okay for them.”

A fishery collapse would have profound economic consequences for the Barents region. The cod fishery is the most important fishery in the Barents Sea, and was valued at NOK 4.8 billion (€570 million) in 2014.

Sundby said that, to avoid the business-as-usual scenario, global annual carbon emissions must start to decline within the next two decades.

“We have 20 years,” he said. “Not much more.”