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Last Thursday, scientists described how rapidly warming water and ineffective regulations led to the collapse of the Gulf of Maine cod population. Last Tuesday, scientists described cod’s remarkable comeback just 1,500 kilometers north, off the coast of Newfoundland and Labrador.
How to explain the difference?
Owing to a host of factors—including human interference—the two regions are far less similar than their geographic proximity suggests.
In each paper, the researchers point to reasons that led to the decline of North Atlantic cod stocks: changes to the ocean environment, overfishing, and the response—or lack thereof—of regulators.
Atlantic cod, at the top of the food chain, can grow two meters long and swim in shoals dozens of kilometers wide. They have been a cornerstone of diets and economies from New England through Atlantic Canada for hundreds of years.
At the fishery’s peak in 1968, the industry caught nearly four million tonnes of cod. Cod stocks went bust in 1992 and fish numbers declined steadily until 2008, when fishermen caught fewer than 800,000 tonnes.
The collapse has been particularly bad in the Gulf of Maine. The amount of breeding cod there is just four percent of its healthy maximum, according to the report in Science.
Its authors ascribe the trend largely to changes brought on by global warming. Between 2004 and 2012, water temperatures rose faster in the Gulf of Maine than in 99.9 percent of the world’s oceans. That’s because the Gulf Stream, which brings warm water north from the Gulf of Mexico, has been drifting further north as a consequence of global warming. The Gulf Stream veers east as it passes Maine, so this challenge is unique to the Maine cod.
But humans have also played a part in the stock’s decline. The paper’s lead author and chief science officer at the Gulf of Maine Research Institute, Andrew Pershing, says regulators mismanaged the region’s cod.
For two years regulators delayed implementing the strictest quotas in an attempt to buffer fishermen from a weak economy. And when they were finally in place, the limits did not take into account the damage warmer waters were doing to cod stocks.
That meant that even though fishermen were following the rules, they were unknowingly taking more fish than the population could handle. But Pershing doesn’t entirely blame regulators for not understanding the science.
“Given the rapid pace of change in the Gulf of Maine, I think it would’ve been asking a lot to expect that people would have recognized the changes and made the linkages to cod,” he writes in an email.
Meanwhile, Canadian cod have benefited from stricter regulations. Canada banned all cod fishing after the 1992 collapse, although officials are currently allowing a recreational cod fishery. (Norwegian and Russian regulators responded even more quickly to the crash and their fisheries are thriving.)
That moratorium was crucial, says George Rose of Newfoundland’s Memorial University. Rose co-authored the paper on the cod recovery, published in the Canadian Journal of Fisheries and Aquatic Sciences.
“The fish needed to be protected to give them time to respond to more favorable conditions out there,” Rose says.
A period of more favorable temperatures and the rebound of their favorite food, fish called capelin, allowed the Canadian fishery to finally start growing. One population off Newfoundland increased from a few thousand in 2003 to nearly 250,000 in 2014.
“The lesson from Newfoundland is that stocks can be rebuilt but that it requires both good management and favorable conditions. From the Gulf [of Maine], the lesson is that populations on the edge, both in terms of their range and abundance, will be hard to manage without incorporating temperature and other environmental effects [into the management models],” Pershing writes in an email.
Rose believes that it’s only a matter of time before the Canadian commercial fishery reopens. Coastal communities depend on it, both economically and socially. But it is not a decision to be taken lightly, he says.
“The worst thing we could do is try to bring it back too quickly. Nature’s given us a second chance here and we don’t want to blow it.”