"Long before it's in the papers"
October 29, 2015


Warming helped decimate New England cod stocks, study finds

Oct. 29, 2015
Courtesy of National Science Foundation
and World Science staff

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.

Bottom-dwelling fish such as Atlantic cod are often found near structures such as shipwrecks. (Credit: NOAA)

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.

* * *

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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% to 4% of sustainable levels, according to scientists. And even painful cuts to the fishery have failed to slow this rapid decline, surprising both fishers and fisheries managers. Now a report links the events directly to rapid warming of ocean waters. “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 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 despite generally good compliance, 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 increasing water temperatures reduced the number of newborn cod, and may have killed off many young fish. Cod is a cold-water species, 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.