Cod were the backbone of New England’s fisheries and a key species in the Gulf of Maine for centuries.
Today, cod stocks are on the verge of collapse, hovering at 3 percent to 4 percent of sustainable levels, according to scientists. And even harsh fishing restrictions have failed to slow the rapid decline, surprising both fishers and fisheries managers.
Now a report links the events directly to global warming.
“Here is an explanation for why the Gulf of Maine’s cod fishery has not recovered despite significantly reduced fishing,” said Mike Sieracki, program director in the Division of Ocean Sciences at the U.S. National Science Foundation.
A key lesson: “management plans will need to incorporate climate change factors to be effective.”
Between 2004 and 2013, the Gulf of Maine warmed faster than 99 percent of the global ocean, according to the report. The paper attributes the effect to changes in the position of the Gulf Stream, a warm ocean current, and to climate oscillations in the Atlantic and the Pacific—both adding to a steady warming caused by global climate change.
In the face of plunging cod stocks, fisheries managers put a series of limits on fishing, but even these failed to produce a rebound, according to the researchers.
“Fishers stayed well within their limits for cod, and yet stocks continued to decline,” said Andrew Pershing, chief scientific officer of the Gulf of Maine Research Institute and lead author of the study. “This creates a frustrating situation that contributes to mistrust among fishers, scientists and managers.”
But the events also “told us something else was going on… it turns out that warming was driving the decline.”
Pershing and colleagues found that rising water temperatures reduced the number of newborn cod, and may have killed off many young fish. Cod needs cold water, and the Gulf of Maine is at the edge of its geographic range. With further warming, expect more declines, the report authors warned.
The findings are published this week in the journal Science.