Herring swim past Primnoa coral in the Outer Schoodic Ridges area of the Gulf of Maine in the summer of 2014. Researchers say temperatures in some deep areas of the gulf have risen by nearly 9 degrees Fahrenheit over the past 15 years, which has affected seasonal migration habits of endangered right whales. Credit: NOAA

Water deep in the Gulf of Maine has been warming twice as fast as the surface over the past 15 years, causing a significant disruption in the seasonal migration of endangered right whales, according to a new scientific study.

The study is consistent with what many whale researchers have suspected for a couple of years — that warming water in the Gulf of Maine is driving endangered right whales farther north in their seasonal search for food — but the degree by which deep parts of the gulf are getting warmer had not been previously examined.

Overall, in recent decades the Gulf of Maine has been warming faster than 99.9 percent of the world’s oceans, according to previous scientific reports.

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Some portions of the gulf ranging in depth from around 65 feet to 500 feet have been warming as fast as nearly 1 degree Fahrenheit per year from August through February, according to the study, which was published earlier this month in the scientific journal Oceanography. Since 2004, some deep areas have warmed by nearly 9 degrees Fahrenheit, which is roughly twice as much as the fastest-warming waters at the gulf’s surface.

That change in temperature appears to be having a significant impact on the abundance of right whales’ preferred food source, a small copepod called Calanus finmarchicus. As concentrations of the tiny, high-fat creatures drop in the gulf, the whales’ migration patterns have been changing, challenging location-based efforts to protect them from ship strikes and entanglements in fishing gear.

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“The climate-driven changes rippling throughout the Gulf of Maine have serious consequences for the small number of remaining right whales,” Nick Record, a senior research scientist at Bigelow Laboratory in Boothbay, said in a statement. “Climate change is outdating many of our conservation and management efforts, and it’s difficult to keep up with the rapid evolution of this ecosystem.”

Dan Pendleton, a research scientist at New England Aquarium in Boston and a co-author of the paper, said Wednesday that the springtime flow of multiple kinds of copepods southwest along the Maine coast has increased in recent years, leading to greater seasonal concentrations of whales in Cape Cod Bay.

But in some deep areas such as basins and the gulf’s Northeast Channel, the warmer water is suppressing the abundance of Calanus finmarchicus in late summer, when the whales traditionally migrate east to feast on the tiny shrimp-like creatures.

It could be that the copepod, which drifts with the currents, reproduces less in warmer water, or that it has a higher mortality rate as temperatures increase, he said.

“That is where we’ve seen a very high rate of warming,” Pendleton said of Northeast Channel, which is a deep trough east of Georges Bank that connects the gulf to the deeper ocean off the continental shelf.

Pendleton said research for the study did not delve into whether the abundance of Calanus finmarchicus has been increasing in the Gulf of St. Lawrence in Canada, where over the past few years right whales have come into more frequent contact with snow crab fishing gear. He said that, prior to 2015, whale researchers did not spend much time looking for right whales north of Nova Scotia.

“Certainly, it appears there are more [whales in the Gulf of St. Lawrence] than there used to be,” Pendleton said.

Efforts to boost protections for north Atlantic right whales, the population of which is estimated to be a little more than 400 individual animals, has led to additional lobster fishing gear restrictions being developed to reduce the risk of entanglement in U.S. waters.

Concerns about the impact added restrictions are expected to have on Maine’s $484 million lobster fishery prompted Maine’s congressional delegation on Tuesday to ask federal officials to make sure that risk reduction standards are equitable between the United States and Canada, among other things.

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Bill Trotter

A news reporter in coastal Maine for more than 20 years, Bill Trotter writes about how the Atlantic Ocean and the state's iconic coastline help to shape the lives of coastal Maine residents and visitors....