AUGUSTA — Two new scientific studies are highlighting the current and future impacts that rising ocean temperatures will have on lobster, clams and other important commercial fisheries in the Gulf of Maine.

Research on nearly 700 North American fish species predicts Atlantic cod habitat could shrink by as much as 90 percent by century’s end and that lobster populations could shift 200 miles farther north as a result of climate change. Meanwhile, a separate research project suggests Maine’s soft-shell clam industry could collapse unless steps are taken to protect the fishery from green crabs that are thriving in the state’s warming waters.

“Something is out of whack and we need to do something about it. We need to adapt,” said University of Maine at Machias professor Brian Beal, who has studied soft-shell clams for more than 30 years.

The studies are part of a growing body of scientific work seeking to understand – and look beyond – changes that fishermen across the country are witnessing on the water every day.

In the Gulf of Maine, which is among the fastest-warming bodies of water around the globe, cod, northern shrimp and other once-abundant species are experiencing long-term declines despite severe limits on fishing. Meanwhile, southerly species such as black sea bass and squid are edging into New England waters once considered too cold for them.

Research published this week in the journal PLOS ONE used data from more than 130,000 bottom trawls and 16 different climate models to estimate the current and future distribution of 686 fish and invertebrate species along the Atlantic and Pacific coasts.

The models used low and high emissions levels of climate-warming gases to calculate the effects, with the lower forecasts tied to levels set in the 2016 Paris Accord agreement. President Trump has withdrawn the U.S. from that agreement.

Overall, the research predicts hundreds of species will shift northward, further disrupting some of the nation’s most important commercial fisheries. In Maine, some of the state’s most economically and culturally significant species – including lobster, scallops, shrimp and groundfish – could find the cooler waters to the north in Canada more hospitable if ocean temperatures continue to rise at the current pace.

The study led by researchers at Rutgers University predicted that:

• The remaining U.S. Atlantic cod habitat – primarily off New England’s coast – could shrink by 90 percent by 2100.

• Lobster distribution could shift another 200 miles north, putting more of the crustaceans in Canadian waters and out of reach of Maine fishermen.

• Likewise, populations of Atlantic sea scallops that fetched Maine fishermen $9.3 million last year could shift more than 430 miles northward.

“It’s quite striking how fast the Gulf of Maine is warming and is projected to warm in the future, so we do expect large impacts on the Gulf of Maine,” said Malin Pinsky, an associate professor at Rutgers University’s Department of Ecology, Evolution and Natural Resources and one of the lead authors of the study. “Some species are moving out, but other species are moving in. And so, from a fisheries perspective, the question is can fisheries managers figure out that transition?”

Maine fishermen landed nearly $570 million worth of seafood last year, making commercial fishing one of the state’s largest industries.

Maine’s lobster landings fell 15 percent in 2017 to 110.8 million pounds worth an estimated $434 million. That was not unexpected after a string of record-breaking years, but some studies have raised concerns that lobster larvae are declining in numbers.

“It does suggest that the habitat will decline,” Pinsky, a Maine native, said of his group’s study. “The question is, will the habitat decline to a point where it cannot support a fishery?”

SOFT-SHELL CLAM FISHERY AT PARTICULAR RISK

The Gulf of Maine is warming faster than nearly every other part of the world’s oceans, according to studies by the Gulf of Maine Research Institute and other organizations. A recent study by scientists at the National Oceanic and Atmospheric Administration predicted that surface waters in the Gulf of Maine could warm by 6.7 degrees over the next 80 years, which is twice the warming rate witnessed over the past 30 years.

As waters warm, they become less hospitable to the cold-loving species such as cod and other groundfish that were the backbone of the coastal New England economy for hundreds of years. Like in Pinsky’s broader study, the NOAA research suggests the Gulf of Maine could experience sharp declines in groundfish abundance in the coming decades.

The temperature rise, combined with other climatic changes, also affects the abundance of important food sources, such as phytoplankton. A 2016 study by researchers at Bigelow Laboratory for Ocean Sciences in East Boothbay, for instance, found that increased precipitation over the past 80 years and the resulting surge in freshwater has changed the color of the Gulf of Maine, making it more difficult for phytoplankton to compete for sunlight needed to survive.

Beal’s research group at the University of Maine at Machias, meanwhile, says the changes have already had dramatic effects on southern Maine’s soft-shell clam population. And without an “introduction of some revolutionary thinking to the clam industry,” Beal said, Maine may not have much of an industry left in the near future as one of the most voracious invasive species in Maine, the green crab, spreads and multiplies in the warming waters.

In research conducted largely around Casco Bay over a four-year period, Beal compared clam survival rates inside special contraptions designed to keep out predators with clams in the adjacent mud. And the results were striking: They found hundreds or even thousands of clams ranging in size from one-eighth of an inch to 1½ inches inside the simple “boxes,” but just outside of the protected area there were practically none.

“There are a variety of predators, so it’s not just green crabs and milky ribbon worms,” Beal said. “There are fish … and birds that prey on clams, but I would say the most important predator that is preying on clams is the green crab.”

A native of Europe, green crabs have been in Maine waters for roughly a century. But their numbers have exploded in the past decade, a trend that Beal and other researchers say is directly tied to warming waters. That’s because the small crabs’ predation rate and reproduction increase in higher temperatures.

Back when Beal began conducting professional research in the mid-1980s, it was possible to get survival rates of 50 percent to 60 percent for young clams placed in unprotected areas. Now they are seeing survival rates of 5 percent or less. In some areas of Casco Bay, less than 0.01 percent of juvenile clams survived beyond their first year, he said.

‘WE NEED TO … ADAPT’ TO GREEN CRABS

In 2017, Maine reported the smallest commercial clam harvest – 6.9 million pounds worth $12.4 million – since 1930. Although harvesting closures because of harmful algal blooms caused part of that drop, the number of licensed clammers in the state has fallen by roughly 75 percent since the mid-1970s.

“We are going to lose an iconic fishery, and we are going to lose it either because people don’t care about it or they just don’t believe” in the science, Beal said.

Beal said towns or individuals need to begin using some form of predator-exclusion devices, which he believes would be workable on plots of 2 to 5 acres. Beal said the state also needs to protect the largest and most reproductively valuable clams from harvesting – as is done in the lobster fishery – while instituting “rolling closures” along the coast that protect clam flats during peak spawning times.

Acknowledging the politics of climate change, Beal said the reality is the Gulf of Maine is warming regardless of whether people want to debate the reasons why. He and other researchers would like to see water temperatures decline, yet the current trend and the models suggest that is not likely. And that means green crabs will likely continue to flourish in the warming waters off Maine’s coast.

“There is no predator that can even match the prowess of the green crab,” Beal said, noting that the species thrives along all types of shoreline and eats almost anything but appears to have a special appetite for shellfish. “They’re here and no one is going to fish them out. So what we need to do is adapt to them.”

Pinsky, with Rutgers University, said he hopes his group’s study will “lay bare some of the choices ahead of us” as policymakers debate how aggressive to be in seeking to limit emissions of climate-warming gases.

“Sticking to the Paris agreement would help our fisheries significantly,” he said.

Kevin Miller can be contacted at 791-6312 or at:

kmiller@mainetoday.com

Twitter: KevinMillerPPH

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