New England. Before Tom Brady, three-way sandwiches, or trips to the packy, the region's residents shared a cultural identity defined mostly by the cod fish. But a fishing technology boom coupled with bad management led to the fish's collapse in the early 1990s. Cod never bounced back, and warm water could be part of the reason why.

The Gulf of Maine—cupped by Cape Cod, capped by Nova Scotia—has been getting about .03˚C warmer every year since 1982. But cod are cold water fishes, and the warmer waters mess with their biology in bad ways. It also changes the prey available to them, and exposes them to new predators. Added up, that means fewer fish. A new paper in the journal Science says these rising temperatures have contributed to cod's dwindling numbers, and should be considered when calculating future fishing regulations.

New Englanders have harvested the sea for centuries, and up until a few decades ago cod was their biggest cash crop. In the 1960s, new technology like sonar and radar let fishermen catch more fish, as well as selectively target older, larger fish. Unfortunately, marine ecologists and fisheries managers didn't experience a similar technological boon. Without knowing crucial ecological information—Where do cod migrate? How do cod reproduce? Just how many cod are there?—fisheries managers couldn't write regulations that kept up with the record number of cod being pulled out of the ocean.

Around 1992, the Northwest Atlantic cod fishery crashed. Fish stocks were around 1 percent of their historic levels. Since then, despite decades of severe catch limits, cod has not come back, and nobody totally understands why.

Sea temperature is a part of that equation. "Temperature affects cod in every way you can imagine," says Michael Fogarty, head of ecological assessment at NOAA's Northeast Fisheries bet365体育赛事 Center. Cold water-adapted cod have speedier metabolisms in warm water, which means they need more food. But those meals aren't always around. So cod are smaller, and fewer survive to reproduce.

"And the fact that they are constantly out looking for food can lead to more mortality, because the fish are being risky and showing themselves to predators," says Andrew Pershing, chief scientist at the Gulf of Maine Research Institute and lead author of the study. He says there seem to be plenty of other ways warmer water affects cod, but biologists and ecologists have yet to tease them all out.

The study found that the Gulf of Maine has been warming at a rate faster than 99 percent of the world's ocean water. This warming—which was particularly fast over the last decade—has coincided with stringent catch limits. In 2013, for instance, Gulf of Maine cod fishermen were only allowed to catch 25 percent of what they'd caught in 2011. And still the fish aren't rebounding. "I don’t think there’s any doubt up here that climate change is very real," says Tom Nies, executive director of the New England Fisheries Management Council. "And it's affecting fisheries in ways we’re just beginning to understand."

So what's causing the Gulf of Maine to warm so quickly? "We think two things are going on," says Pershing. One is the Gulf Stream. "The Gulf Stream responds to wind patterns, and also to the distribution of warm and cold water in the Atlantic," says Pershing. "You can think of it really as an area of warm water in the North Atlantic that just expands." That expansion has lined up with a long term sea surface temperature oscillation that brought warmer water into the northwestern Atlantic—on top of the steady global warming trend.

For fishermen who have faced decades of slashed quotas, this is more bad news. "My expectation is this paper will get a lot of closer looks, and it may lead to changes in the way quotas are set," says Nies. "But if you look at the quotas, they are already pretty darn low. It would be difficult to set them any lower and still have quotas at all."

And those low quotas don't just affect cod fishermen. Bycatch rules means that even fishermen who are out targeting things like like haddock and pollock can have their seasons end early if they inadvertently bring aboard too many cod. The fish is a choke species.

But Nies sees a bright side. "If you get to a point where you are setting quotas correctly, you get biological results," he says. Even under the most pessimistic regulatory scenario, a stock should eventually become commercially—and ecologically—viable. And this study is a first step in setting informed limits: Pershing is one of the scientists who makes quota recommendations to the New England Fishery Management Council.

Pershing says making these calculations is hard, and not just because they determine the survival of cod in the Gulf of Maine. "The decisions being made affect people's families," he says. At least in the short term, things are looking wicked bad for fish and fishermen alike.