Something alarming is happening in the Gulf of Maine

A new study in the journalSciencefound that the once plentiful cod fishery in the Gulf of Maine, the coastal body of water that stretches from the north shore of Massachusetts up to the Canadian Maritimes, is headed for collapse.

The culprit? Climate change.

Andrew Pershing, the study’s lead author and the Chief Science Officer of the Gulf of Maine Research Institute, told Business Insider that warming sea surface temperatures negatively affect cod populations, but the actual reasons aren’t totally clear yet.

The Gulf of Maine is at serious risk because it’s warming so rapidly — 99.9% faster than the rest of the world’s oceans, according to the study.

The level of warming and the speed at which it’s happening is unprecedented, even for a highly variable part of the ocean like the Gulf of Maine, according to scientists.

“We’re moving into this new reality where we’re seeing ecosystems pushed way beyond our historical reference points,” said Pershing.

A big reason behind the collapse, the study found, is that when the government sets cod quotas for commercial fishing operations, they don’t account for environmental factors — specifically, warming sea surface temperatures. This has proved disastrous for bodies of water that are changing as rapidly as the Gulf of Maine.

Typically, managers of fisheries set quotas based on a simple feedback model. “Basically the assumption is that fishing is the main driver on the population,” said Pershing. “You look at the stock, and if it’s down, you pull the quotas down. If you’re no longer catching as many fish, that should allow the population to rebound.”

According to Pershing’s study, this assumption breaks down if the environment moves quickly away from average conditions, like the Gulf of Maine has in the past decade.

Previously, sea surface temperature was not thought to have a major effect on cod populations. It’s only because the Gulf of Maine has warmed so extremely that scientists began to see an obvious effect.

“Temperature just hadn’t been recognised as a major driver of cod populations before,” said Pershing. “It’s one of those catch-22s where you see the effect of temperature only because we’ve had such a big effect in the last ten years.”

On the graph below, you can see how warming sea surface temperatures correlate with declines in cod spawning stock over the last 35 years:

This knowledge is surprisingly new. Fisheries’ quotas, determined by regulators through careful estimations, simply do not take temperature into account.

So while the Gulf of Maine is warming and becoming increasingly inhospitable to cod, they are still being fished at the same rate. And now, this has resulted in rampant overfishing.

“What I’m really trying to highlight with this work,” says Pershing, “is that we need to account for environmental change in our models.”

Still, while the effect the warming oceans are having on cod populations is clear, the actual mechanism driving this warming is less clear. “In the paper, we lay out some hypotheses, but we really don’t know what’s driving it yet,” said Pershing. “That’s really something I hope people will start to look at in the future.”

And, the study isn’t all bad news. Some other fish species, for example, could be unaffected by the change or even affected in the opposite direction, said Pershing. “The conditions that are good for haddock are bad for cod,” Pershing said. “So the boom we’re seeing now in haddock could be related to the same mechanisms.”

As for now, fishermen and regulators alike will be forced to adapt to a new normal in the Gulf of Maine.

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