BOSTON – An entangled right whale that researchers have attempted to save numerous times during a widely followed, three-month struggle may have died, scientists said.

Scientists at the Center for Coastal Studies said the last time they received a signal from a telemetry buoy attached to the North Atlantic right whale, known as Churchill, was Sunday afternoon.

David Mattila, director of the center’s disentanglement program, said the lost signal may mean the buoy is underwater, an indication the whale might be dead.

“Although most healthy right whales naturally float, this whale has lost so much weight that if he has died it is possible that the carcass would sink, taking the tag down with it,” Mattila said.

The water pressure would destroy the buoy, scientists said.

The 50-ton whale was first spotted June 8 off Cape Cod with a synthetic marine rope jammed in its mouth. The whale is one of only about 300 North Atlantic right whales left in the world.

Extensive efforts were made to disentangle the whale, including the first-ever attempt to sedate a right whale in the wild. But six rescue attempts failed, thwarted by poor weather and inadequate doses of the sedative, among other things.

Scientists warned from the start of the rescue attempts that the whale, a breeding male, was likely doomed because of an infection spreading from the wound caused by the marine line.

After the last rescue attempt Aug. 30, experts said whale lice had spread on the animal, an indication the infection was worsening.

The whale was last spotted about 400 miles off New Jersey, swimming in an area about 15,000 feet deep. Some scientists held slim hope the whale was still alive.

“It is possible that we are experiencing a technical difficulty and that the tag will start transmitting again,” said Bob Bowman, the Center researcher in charge of tracking Churchill. “However, we believe that this may mark the end of our long rescue effort on this unfortunate animal.”