Climate change isn’t yet coming for your fish and chips—but it has taken Gulf of Maine cod off the menu for most people. An analysis of how cod react to warmer waters shows that the fishery is failing despite strict quotas because climate change has warmed the gulf much faster than the rest of the ocean.
“We suspect that there may be other species, in the northeast and elsewhere, that are being impacted by warming waters in a similar way,” says study leader Andrew Pershing, chief scientific officer of the Gulf of Maine Research Institute.
Atlantic cod are found from the U.S. northeast coast, north to Canada and across the North Atlantic as far as the Barents Sea north of Russia. The northwest Atlantic population, off the United States and Canada, has been chronically overfished and eventually crashed in the 1990s. Fishery managers instituted deep cuts in quotas for commercial fishers, and the recreational fishery is now closed.
Such measures worked in the waters off Newfoundland, scientists reported October 27 in the Canadian Journal of Fisheries and Aquatic Sciences. But in the Gulf of Maine, closer to the cod’s southern limit, the fish continued to decline.
Oceans around the world have gradually risen in temperature as excess greenhouse gases in the atmosphere have warmed the globe. Warming in the Gulf of Maine, though, has been much faster, and Pershing and his colleagues suspected that might be affecting cod.
As they report today in Science, between 2004 and 2013, the Gulf of Maine warmed an average of 0.4 degrees Fahrenheit per year, faster than 99.9 percent of the rest of the ocean. That warming is happening because the Gulf Stream is moving north as winds have changed, and “some of the warm water it carries is able to work its way into coastal waters, including the Gulf of Maine,” explains coauthor Michael Alexander of the National Oceanic and Atmospheric Administration’s Earth System Research Laboratory.
The Gulf Stream may also be affected by Arctic warming, Alexander says. That warming melts sea ice and releases cold freshwater into the North Atlantic. That cold water is projected to slow down a huge ocean current called the Atlantic meridional overturning circulation, and it may also play a role in the Gulf Stream’s northward migration.
When the researchers looked at how these warmer waters affected cod, they found fewer cod larvae and juveniles survived until adulthood. The death rate for older fish also went up. This was why the fishing quotas didn’t work. The quotas rely on assumptions about how many fish of various ages survive from year to year, but those assumptions were wrong.
Managers of the Gulf of Maine cod fishery currently don’t take temperature into account when determining fishing quotas, but Pershing says doing so “needs to be a priority.” Right now, quotas are set so low that the fish population should eventually recover, he says. But with warming temperatures, expectations about how fast the cod fishery could rebuild and how large it can get have been unrealistic, the researchers say.
Cod-lovers shouldn’t worry about eating the fish, though. “Most cod in the [United States] is now imported from places like Iceland and Norway or is Pacific cod from Alaska,” Pershing notes. “These stocks are currently doing well.”
But Gulf of Maine cod could be just the beginning. “We are seeing a remarkable change in this ecosystem,” Pershing says, “and we need to figure out the short- and long-term impacts on the species we care about.”