Rescuers who helped free more than 100 dolphins from the Cape Cod coast say they have confirmed that the mass stranding that began June 28 was the largest involving dolphins in U.S. history.
There have been two previous recorded events in Hawaii and the Florida Keys where dolphin species were observed circling in shallow water, but the Cape Cod event marks the largest number of dolphins stranded in a single stranding, according to the International Fund for Animal Welfare, which helped lead the rescue.
A final review of data and aerial imagery this week revealed that a total of 146 dolphins were involved in the stranding, according to IFAW communications director Stacey Hedman.
The group estimates that 102 dolphins survived the event, which lasted several days. There were 37 natural deaths and seven dolphins that had to be euthanized.
Response efforts continued on a smaller scale, including the rescue, relocation and release of nine of the same Atlantic white-sided dolphins on July 2.
That day, 11 dolphins were found stranded near Powers Landing in Wellfleet, Mass. Two were euthanized and nine were transported to a custom-built mobile dolphin rescue vehicle, where veterinarians and biologists can administer fluids and other treatments en route to a deeper-water location, Hedman said.
In this case, she explained, the dolphins were released near Herring Cove Beach in Provincetown. Satellite tags allowed several of the animals to be tracked safely offshore.
There is no specific reason why the dolphins stranded.
Rescuers faced many challenges as they tried to guide the dolphins back to open water, including difficult muddy conditions and the fact that the dolphins were spread out over a large area.
In some rescue attempts, workers have started on foot, herding the creatures into deeper water, and then used small boats equipped with underwater detectors, which make noise to help lure the creatures.
Several dolphins have died at The Gut, or Great Island, in Wellfleet on the Herring River. The Gut is the site of frequent strandings, which experts say is due in part to its hooked shape and extreme tidal fluctuations.
“This stranding response was a massive effort by our staff, volunteers and partners over several days,” Hedman said, adding that with a survival rate of about 70 percent, the group considers the response a success.
The organization has also received reports from whale-watching vessels that have seen some of the dolphins – identified by temporary tags – now swimming among other groups of hundreds of other dolphins that were not involved in the stranding.
More than 25 IFAW staff and 100 trained volunteers participated in the rescue operation. The group also received support from Whale and Dolphin Conservation, the Center for Coastal Studies, AmeriCorps of Cape Cod and the New England Aquarium.
