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North Atlantic right whales spotted early in Cape Cod Bay

Officials said the whales are here to feed on zooplankton.

Provincetown Center for Coastal Studies

Officials said the whales are here to feed on zooplankton.

Fifteen rare North Atlantic right whales were spotted feeding in waters off Wellfleet Thursday, the earliest sighting of the whales in Cape Cod Bay in nearly 30 years, the Provincetown Center for Coastal Studies said.

“It is earlier than usual,” said Charles “Stormy” Mayo, director of right whale habitat studies at the center. “Our airplane is up right now circling them.”

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With a population of 502, the North Atlantic right whale is one of the rarest baleen whale species. They historically appear in the bay from mid-January to early May. Last year, more than 200 of them were spotted off Cape Cod.

Two whales were accidentally discovered Wednesday by the center’s disentanglement team, which was bringing a boat into a harbor for repairs. Fifteen more were seen by aerial researchers Thursday. The observations of the population feeding in the bay were the earliest in 27 years, Mayo said.

“They’re here because of food; there’s no question about that,” Mayo said, adding that the right whale feeds on the microscopic organism, zooplankton. “Cape Cod is a very rich place.”

Mayo suspects that the whales are arriving earlier because of the Atlantic Ocean’s temperature changes. Last year, the ocean measured about 3 degrees warmer than average, which Mayo said is a significant increase.

The center’s aircraft have been taking photographs of the whales. The center works with many agencies to use the photographs to identify and track the whales, study environmental stresses, and the overall health of the population, Mayo said.

Sarah N. Mattero can be reached at sarah.mattero@globe.com.

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