PROVINCETOWN — Marine mammal experts predict the mass stranding of common dolphins along the Cape Cod Bay coastline could continue for many days, given new sightings Monday.

In Provincetown Harbor on Monday, rescuers kept a close eye on 75 common dolphins that were acting erratically and appeared close to stranding, Scott Landry of the Provincetown Center for Coastal Studies said.

The center's aerial survey team, in flight on Monday to count North Atlantic right whales, counted at least 300 dolphins in Cape Cod Bay, including those in the harbor, Landry said.

In the past five days, about 40 to 50 dolphins have been reported stranded over 25 miles of coastline from Dennis to Wellfleet, said Katie Moore, marine mammal rescue director for the International Fund for Animal Welfare in Yarmouthport.

Of those, 27 have been found alive and 19 have been released in local waters. Six dolphins that stranded on Wellfleet beaches on Monday were released at Herring Cove Beach in Provincetown, Moore said.

The common dolphin typically makes its home in waters deeper than Cape Cod Bay and farther from the shoreline. The ones in the area now may be attempting to head south but have gotten caught in the bay, Landry said.

The 75 dolphins in Provincetown Harbor appeared to have righted themselves and headed out to safer waters, Landry said Monday evening.

"We don't think this is over," he said. "It seems pretty likely that this stranding is going to be protracted unless something radical changes."

The coastal studies center works under the direction of the Yarmouthport animal welfare organizations to respond to the strandings, Landry said.

Dolphin strandings have occurred for hundreds of years, Moore said. The exact cause is not known but may relate to dolphins' tendency to follow one another, she said, and if the leader becomes disoriented or ill, the dolphins can run aground.

The last mass stranding on Cape Cod, when there was more than a month of activity, occurred in the winter of 2005 and 2006, Moore said.

"I'm hoping this doesn't last quite as long," she said.

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