Gayathri Vaidyanathan, Science Writer

PNAS Aug. 8 2017

Figure: Starting around 2009, climate-induced migration of mackerel stocks sparked squabbles among several nations that had traditionally shared the fishery. Image courtesy of Shutterstock/Rich Carey.

Denmark, Ireland, Norway, and multiple other nations didn’t see the fish war coming. In 2011, in the waters and fjords of east Greenland, fishermen began spotting a blue-green iridescent fish. It was mackerel, a species that had never before been caught so far north. By 2014, the fish was one of Greenland’s most valuable exports, generating $100 million in sales (1).

Mackerel had previously ranged in the balmier waters off the Faroe Islands, Denmark, Iceland, Norway, and Scotland. Dating back to 1999, these nations had an agreement divvying up the fishery. Then as the ocean warmed, the stock began expanding northward, first to Iceland in 2009 and then to Greenland (2).

A carefully arranged agreement was suddenly in disarray. After Iceland and Greenland set up their own quotas, the historic mackerel nations tore up their agreement and sanctioned the new entrants for daring to hunt the fish. Efforts to renegotiate a new contract and set a collective, sustainable catch limit have failed. Mackerel is now being overfished by 48% above sustainable levels (1). “The stock will decrease if the fishery continues at this rate,” says Teunis Jansen, a fisheries scientist at the Technical University of Denmark. “But there is no country that has an interest in being responsible and cutting down on their national quotas.”

The case of the mackerel has analogs elsewhere. The blueline tilefish, which was once found only in the southeastern United States, has shown up north of Cape Hatteras. The black sea bass, which used to be centered off Virginia, is now centered off New Jersey. As climate change has heated up the oceans, some of the world’s most valuable fisheries are declining in productivity or shifting their distribution, thereby pitting nations, states, and fishermen against one another.

But there is hope. If governments manage their coastal resources well, fisheries globally could rebound by 2100, even in a warming world, according to new research based on a comprehensive modeling initiative that incorporates fisheries science, economics, and climate change. “This is added motivation to get our act together and fix fisheries because if we do that, the future can be more prosperous than today,” says Steve Gaines, a fisheries scientist at the University of California, Santa Barbara.

See http://www.pnas.org/content/114/32/8435.full