BLUE HILL — Changes in the ocean’s temperature may be keeping more right whales in the Gulf of Maine, or at least leading them to stay here during more of the year, and bringing them closer to shore.

Andrew J. Pershing of the Gulf of Maine Research Institute and a professor at the University of Maine School of Marine Sciences said more right whales in the Gulf of Maine would be a “nightmare” for lobstermen.—STAFF PHOTO BY STEPHEN RAPPAPORT

Speaking last week at the Marine Environmental Research Institute (MERI) in Blue Hill, Pershing explained that right whales feed primarily on a nearly microscopic form of plankton, a copepod of the species Calanus.

During the summer months, that is one of the most abundant copepods in the Gulf of Maine. That abundance, in part, is what attracts large aggregations of right whales to the waters off the coast of Maine to feed.

Weighing in around 63 tons, the right whale “is the second largest animal you’re likely to see in the Gulf of Maine,” Pershing said. The fin whale is even bigger.

Despite holding down second place, the typical right whale consumes some 1,500 pounds of plankton, mostly copepods, generating about a half-million calories — daily. So the connection between the amount of plankton in the water, and where it is concentrated, has a direct impact on where the whales are.

It has long been known that the Gulf of Maine is a rich feeding ground for right whales. It was also well known that pregnant females headed south for the winter to calve.

Until recently, no one really knew where male right whales, and females that weren’t calving, spent the cold months of the year. Earlier this month, though, scientists from the National Oceanic and Atmospheric Administration’s National Marine Fisheries Service discovered a pod of the giant animals disporting themselves in the waters of the Jordan Basin, about 70 miles south of Bar Harbor. Scientists first spotted what is believed to be the same group of whales in mid-December off Gloucester, Mass.

Pershing said the congregation of whales suggests that the Gulf of Maine might be “the long unknown right whale breeding ground.” Scientists still have plenty of work to do, he added, before they can be certain of that.

According to Pershing, among mainstream scientists “there is a general acceptance that climate change is real, and a product of human activity.” The phrase “climate change” encompasses much more, though, than warmer temperatures.

Using increasingly sophisticated computer models, scientists are making confident predictions about the melting of ice in the Arctic and increases in the amount of precipitation in the Northern Hemisphere. Those models show that the decreasing salinity of the northern oceans, including the Gulf of Maine, from the 1950s to the 1990s is likely to continue.

One result of the change in salinity in the Gulf of Maine appears to be that plankton that usually disappear during the warm months when the warm water is nutrient-poor are now showing up in the cooler fall and winter months. The result has been blooms of plankton — whale food — in places and at times of the year when they didn’t occur in the past. That can have major implications for fisheries management decisions.

Under current federal fisheries regulations, lobstermen fishing in the Gulf of Maine beyond an “exemption line” that runs close to the coastline, must use fishing gear that is modified to reduce the risk of entangling feeding right whales and other large whales. The question facing fisheries managers, Pershing said, is whether that exemption line is in the right place.

Lobstermen say they never see whales close to shore and want the exemption line pushed into deeper water. Conservation groups argue that whales do feed inshore and that the exemption line is too liberal.

According to Pershing, the Maine Department of Marine Resources (DMR) has begun a study of what climatic conditions could bring large numbers of copepods into nearshore waters. If it turns out that that the one effect of a warming climate is the concentration of Calanus copepods close to the coast, it could mean that many more Maine lobstermen could face the need to make extensive, and expensive, modifications to their gear if they want to continue to go lobster fishing.