About 50 right whales have been spotted unusually close to the coast of Cape Cod Bay, from Duxbury to Sandwich, over the past week, a whale researcher said Thursday.
“People can get a very close view of these rare animals,” said Charles “Stormy” Mayo, director of the right whale research program at the Provincetown Center for Coastal Studies. “They should take advantage and walk along the beaches.”
About 75 right whales have been in the bay since December, based on the center’s aerial survey. That number has gradually increased, with 82 whales being recorded in the area Wednesday, Mayo said. Many of them are mother and calf pairs.
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Some of the whales have been moving closer to the shore and near the mouth of the Cape Cod Canal, as they follow their food supply of microscopic plankton, he said. They are concentrated along the southern inner shore but have been spotted near the coast as far north as Duxbury. This same behavior was seen two years ago.
“They’re skimming plankton right off the surface,” Mayo said in a telephone interview. “Their huge heads are just protruding from the water. People might think they look like huge rocks moving through the water.”
Plymouth Assistant Harbormaster Patrick Logan said Wednesday that in the past week, about a dozen sightings had been reported at Manomet Point and at the entrance of the Plymouth Harbor Channel.
It is dangerous for the whales to be so close to the shore, Mayo said, particularly as fishermen begin working more in the spring. They can get hit by boats or become entangled in fishing gear.
“There is increased boat traffic now in May, and they’re notorious animals for being hit by small ships and boats,” Mayo said.
One whale was struck in the Bay Sunday, according to Ally Rogers, a spokeswoman for the law enforcement office of the National Oceanic and Atmospheric Administration in Maryland. She said the incident was under investigation.
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Mayo said his research team found a whale Wednesday with deep propeller scars.
“The animal appears to be healthy,” he said. “It does not appear the damage could be lethal, but it is hard to be sure from an aerial view.”
The Coast Guard has issued a warning to mariners to decrease their speed in the area and to be on the lookout for whales. A Coast Guard spokesman said the agency was unaware of the whale strike in the bay Sunday.
Right whales are an endangered species, and federal law prohibits mariners from approaching them within 500 yards.
The whales visit the Cape Cod Bay annually but do not usually get so near the shore. Mayo said he expected them to move farther away soon.
Aneri Pattani can be reached at aneri.pattani@globe.com. Follow her on Twitter @apattani95.