About This Species
When Europeans first arrived in America, among the bounties they discovered were giant, plentiful Atlantic cod. The fish choked the harbors of the Northeast, making for easy fishing. Some cod, people said, were as big as men.
The cod caught these days are far smaller, typically 2 to 3 feet. Though they can survive in temperatures from 30-68 degrees Fahrenheit, they are usually found in temperatures ranging between 32 and 53 degrees Fahrenheit. In North America, their range extends as far south as Cape Cod to the northernmost point of Labrador.
Their size, reproduction and spawning times are linked to temperature. Scientists have found that the fish feed more when in an optimal temperature range. At the extreme ends of that range, they eat less and are smaller. Also, warmer temperatures can cause the fish to mature slower and to spawn earlier.
Cod populations in several areas declined through the '90s, due to a combination of overfishing and climate change. In some of those areas, even the cessation of fishing has not helped the population rebound, but they have made gains in others.
The Gulf of Maine, where sea surface temperatures have increased faster than 99 percent of the oceans worldwide, has seen a precipitous drop in cod. Andrew Pershing, the chief scientific officer at the Gulf of Maine Research Institute, wrote in a 2015 study in the journal Science that as the waters warmed, they were no longer an ideal temperature for the species, but it was not immediately recognized by the fishing industry.
As cod stocks along the southern, warmer parts of its range have been depleted, they are booming along the northern part of the fish's range, like Labrador and Newfoundland.
"Every species has its optimal temperature," Pershing said in an interview. "As the northern Atlantic has warmed up, the ecosystems at the northern end of the cod's range, the cod stocks there have become optimal temperatures."
A study published in the ICES Journal of Marine Sciences in 2005 looked at how cod populations would be impacted by global warming. It found that as the Atlantic warms, some would decline or disappear, while others would increase.
At 1 degree Celsius of temperature rise, the study found that stocks along the southern edge of the range, like Georges Bank in Cape Cod and the Irish Sea, would suffer, while the stocks further north could increase. In the 12 years since that study was published—and as global temperatures have increased to more than 1 degree Celsius above preindustrial levels—Pershing said those predictions have borne out. As temperatures continue to rise, more areas are expected to see declines, while a few in Labrador and Newfoundland, will increase.