Researchers at the New England Aquarium in Boston say another North Atlantic right whale has died.
The aquarium's right whale research team tweeted that the dead whale was a female named "Couplet."
Melissa Munro of Sierra Club Canada says "Couplet," who mothered five calves, was found last Monday in the waters off Cape Cod.
Ten of the endangered mammals have died in the Gulf of St. Lawrence since early June – at least some after colliding with ships.
The Canadian government has ordered vessels to slow down in parts of the gulf as it tries to protect right whales who frequent the waters.
It's estimated there are only about 500 North Atlantic right whales still alive.