A North Atlantic right whale breaks the ocean surface off...

A North Atlantic right whale breaks the ocean surface off Provincetown, Mass., in Cape Cod Bay on April 10, 2008. Credit: AP / Stephan Savoia

The National Oceanic and Atmospheric Administration’s Fisheries division and Canadian authorities are launching an investigation after a number of North Atlantic right whales have died this summer, stressing the already imperiled population.

Thirteen of the critically endangered mammals have died since April — 10 in Canada’s Gulf of St. Lawrence and three at or near Cape Cod and Martha’s Vineyard, Massachusetts, said David Gouveia of NOAA Fisheries Greater Atlantic Region.

“The recent right whale mortalities are concerning,” Gouveia said during a news briefing Friday.

The investigation, coordinated with Fisheries and Oceans Canada, will focus on cause of death, changing habitats, food distribution, pathogens and other factors.

Right whales are one of the most endangered large whale species in the North Atlantic. Their population hovers between 450 and 500.

“Thirteen animals is a lot of animals when you talk about a population of less than 500,” said Sean Hayes, chief of the Protected Species Branch for NOAA’s Northeast Fisheries Science Center.

On average, the species loses 3.8 whales a year, making this year’s tally troublesome, especially considering this was one of the worst calving years in nearly two decades.

“When number of deaths is high and number of births is low . . . it’s difficult to recover a population,” Hayes said.

The whales typically migrate from Florida north along the Eastern Seaboard to Canada and back again as they feed, breed and birth calves.

They have been seen sporadically from shore and air surveys during the winter, said Rob DiGiovanni Jr., founder and chief scientist for the Atlantic Marine Conservation Society based in Hampton Bays.

“This is a normal migratory route for them passing by here,” he said.

The animals got their name as the “right whale” to hunt because they are slow movers, feed near the surface and float when dead. Long Islanders were known to hunt them before commercial whaling was outlawed.

They were listed as endangered under the Endangered Species Conservation Act in 1970. The biggest threats to the population come from collisions with ships and getting tangled in fishing and lobster gear.

Those are the primary suspected causes in this recent spate of deaths, said Matthew Hardy, manager of the Aquatic Resources Management Division for Fisheries and Oceans Canada.

The investigation of what is officially called an “unusual mortality event” will be used to determine if regulatory changes — for example, modifications to ship traffic or types of authorized fishing gear — are necessary.

“We hope that it will serve to inform better decision-making,” Hardy said.

Latest videos