Rescue workers who helped free more than 100 dolphins off the coast of Cape Cod confirm that the mass stranding is the largest dolphin stranding in U.S. history.
Two other events were recorded in Hawaii and the Florida Keys where species of dolphins were observed circling in shallow water.
However, the Cape Cod incident, which began on June 28, represents the highest number of dolphins stranded in a single incident, according to the International Fund for Animal Welfare, which led the rescue operation.
A final review of data and aerial photos this week found that a total of 146 dolphins were involved in the stranding, according to the fund’s communications director, Stacey Hedman.
The group estimated that 102 dolphins survived the multi-day event.
There were 37 natural deaths and seven dolphins had to be euthanized.
Relief efforts continued on a smaller scale, including the rescue, relocation and release of nine of the same Atlantic white-sided dolphins on July 2.
Several of these animals were safely tracked off the coast using satellite transmitters.
There is no clear reason for the stranding of the dolphins.
Rescuers faced numerous challenges as they attempted to guide the dolphins back to open water, including difficult mud conditions and the fact that the dolphins were scattered over a large area.
“Rescuing the stranded people has been a tremendous effort for our staff, volunteers and partners over several days,” Hedman said, adding that the group considers the relief effort a success with a survival rate of about 70 percent.
The organization has also received reports from whale-watching vessels that have seen some of the dolphins – identified by makeshift tags – swimming among hundreds of other groups of dolphins that were not involved in the stranding.