State officials are asking commercial and recreational vessels churning through a busy section of Cape Cod Bay to slow down and keep an eye out for a large group of endangered North Atlantic right whales.

The Division of Marine Fisheries has issued a high-risk advisory for boats in a large swath of the bay from Green Harbor to Sandwich, an area with a high volume of shipping traffic, the division said in a statement. Sixty to 80 whales have been spotted in the area, drawn by an abundance of zooplankton, which they feed on, the statement said.

“Dense concentrations of zooplankton at the surface and just below the surface are attracting the whales to this area,” the statement said. “Whales feeding in this manner are incredibly difficult to see and at great risk for vessel strike. Vessel strike is a major cause of human-induced mortality for right whales.”

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Approximately 550 right whales still remain, making them the most endangered species of large whale in the North Atlantic, the statement said.

The division is asking vessels not to exceed 10 knots in the high-risk area and to post lookouts to spot the whales, the statement said.