OTTAWA, Ontario — An area of the Gulf of St. Lawrence was closed to snow crab fishing Thursday after an eighth North Atlantic right whale was found dead Wednesday.

Of the eight whales found floating in the gulf since early June, at least half have been identified as also having fed in southern New England waters, including Cape Cod Bay, according to the New England Aquarium.

Snow crab fishing gear poses a risk to the rare whales, according to Fisheries and Oceans Canada, which oversees the conservation and sustainable use of the nation's oceans and inland waters.

Fishing gear entanglement and ship strikes are primary threats to the right whales, the population of which was at 524 in 2015 and is believed to be in decline, according to researchers.

About 98 percent of the total allowable catch for snow crab in Area 12 of the Gulf of St. Lawrence had already been harvested at the time of the closure, the government agency said in a statement.

“We understand the impact this could have on fishers,” the agency said. “However, the recent whale mortalities in the area are unprecedented and this closure is an important measure to address the situation.”

Staff from the National Oceanic and Atmospheric Administration’s aerial survey plane, based in Woods Hole, spotted the eighth dead whale. The survey team is among several from Canadian and U.S. agencies and groups responding to the rash of whale deaths and entanglements in the gulf.

The whales have been feeding in the gulf, which is not an area they’ve typically used in past decades, according to whale conservationist Regina Asmutis-Silvia, of Whale and Dolphin Conservation, an international advocacy group with an office in Plymouth. Fewer measures have been taken to protect right whales in the gulf, such as the seasonal slow-down zones for ships around Cape Cod.

The Canadian coast guard was to tow the eighth dead whale to shore and a necropsy was planned for Friday to determine the cause of death, the agency said.

— Follow Sean F. Driscoll on Twitter: @seanfdriscoll.