This summer on Cape Cod was record-breaking for the International Fund for Animal Welfare, which oversees the rescue of stranded dolphins. In all, 175 dolphins have been rescued in the past three months, including 11 bottlenose dolphins found in muddy flats in Brewster on Monday, the group said.
Researchers are working to determine why strandings have increased, but one possibility is that global warming has changed the behavior of the bait fish that dolphins feed on, said Brian Sharp, IFAW’s director of marine mammal rescue.
“As the climate changes, we’re seeing animals shifting their habitat,” he said. “That shift has caused kind of a domino effect. So small fish come into shore, larger fish come into shore, and that brings dolphins into shore.”
Sharp said that Monday’s rescue of 11 bottlenose dolphins was the largest single rescue involving the species in the Northeast since the 1990s. It involved a subspecies usually found well out to sea and not often seen in Massachusetts waters. And most of the dolphins weighed at least 600 pounds, Sharp said.
When rescuers arrived at Linnell Landing in Brewster, three dolphins had died, but they were able to refloat the mammals once the tide came in, Sharp said.
Before they were released, one dolphin was outfitted with a temporary satellite tag, while others were given temporary identification tags. The effort to collect information for research proved pivotal, since by Tuesday morning the cluster had become stranded again, this time in Wellfleet, according to the IFAW.
IFAW was alerted to the stranding from the location provided by the satellite tag, Sharp said. The animals were trapped at Lieutenant Island, and rescuers realized that conditions prevented their release, even though a high tide was due around 11 a.m.
Instead, crews used mobile dolphin rescue vehicles to bring the dolphins to Herring Cove in Provincetown, where they were set free. On Wednesday, the group was west of Provincetown in Cape Cod Bay.
Sharp said that this week’s high astronomical tide, which raised coastal waters by as much as 12 feet, may have also played a role in the original stranding. Having followed fish, likely striped bass, the dolphins found themselves confused by the steady drop in water levels.
“Whenever we have super high tides like this, we get a tide flux of up to 12 feet. And that makes it so animals swimming close to shore can be caught by that,” he said. “That’s what we think is happening in this case.”
It has been a busy year for dolphin rescues, Sharp said, most notably a mass stranding in late June of 146 Atlantic white-sided dolphins.
“Typically in a year, we have about 70 live dolphins, and that alone makes us the busiest location in the world,” he said. “So you can imagine 175 in just three short months — it just really puts it on a different level.”
John R. Ellement can be reached at john.ellement@globe.com. Follow him @JREbosglobe.