Normally, the Coast Guard is on the lookout for mariners in need of help. But on Sunday crew members aboard a 270-foot cutter stationed in Portsmouth, Va. spotted a more welcome sight: two right whales swimming northwest of Menemsha in Vineyard Sound.

The sighting was made at 9 a.m. Sunday, according to Tim Cole, a research fisheries biologist at the National Marine Fisheries Service in Woods Hole. “When observed, the right whales appeared to be feeding. They didn’t appear to be in distress,” Mr. Cole said.

As soon as they were spotted, the Coast Guard issued a notice to all mariners in the region telling them to steer clear of the area.

The whales were spotted at latitude 41.39; longitude -70.805, or slightly south of the halfway point between Menemsha and Quicks Hole, a strait in the Elizabeth Islands that separates Nashawena and Pasque Islands.

This is the third significant sighting of right whales in Vineyard waters this year. The first two sightings were made as part of an aerial survey of the endangered whale. Whales were spotted between the Vineyard and Nantucket on Feb. 15; more were seen southeast of the Vineyard on Feb. 26.

“The Coast Guard is an important partner in our efforts to monitor the right whale distribution in the area,” said Mr. Cole, who is charged with keeping track of sightings or right whales in New England waters. The sightings are then reported to mariners transiting these waters, in a broad effort to keep vessels away from the endangered whale.  It is estimated that only about 400 exist in the world today, making them nearly extinct.

The National Oceanic Atmospheric Administration Northeast Fisheries Science Center maintains a right whale sighting web page which is updated regularly.