LONG BRANCH, N.J. — The carcass of a critically endangered species of whale was found floating off the coast of New Jersey on Thursday, federal authorities said.

The whale was a North Atlantic right whale. The whales number only about 400, and have suffered high mortality and poor reproduction in recent years.

The National Oceanic and Atmospheric Administration said the whale was found floating off the coast of Elberon, N.J. The agency and the Marine Mammal Stranding Center are working on performing a necropsy of the animal to determine how it died.

The death was the first observed right whale death in U.S. waters this year. The animals are vulnerable to ship strikes and entanglements in fishing gear. Extensive measures have been taken to protect the whales in the waters off the Northeast.