Another right whale found dead

American researchers in Boston say another North Atlantic right whale has died.
The researchers at the New England Aquarium tweeted over the weekend that the dead whale was a female named ``Couplet.''
The Sierra Club says ``Couplet,'' who mothered five calves, was found last week off Cape Cod.
Ten right whales have died in the Gulf of St. Lawrence since early June -- at least some of them after colliding with ships.
The Canadian government has ordered vessels to slow down in parts of the gulf as it tries to protect the whales.
It's believed only about 500 North Atlantic right whales remain.