102 Dolphins Survived the Largest Mass Stranding in US History, Rescuers Say

Rescuers on Monday announced an "extremely successful" resolution to what has been officially declared the largest mass dolphin stranding in U.S. history, with more than 100 dolphins surviving the ordeal that began last month on Cape Cod.

The nonprofit International Fund for Animal Welfare said a total of 146 dolphins were involved in the stranding that began on June 28 in Wellfleet, Mass ., and 102 are believed to have survived. Of the 44 remaining dolphins, 37 died from natural causes and seven were euthanized.

"The stranding response was a tremendous effort for our staff, volunteers, and partners over several days," IFAW said in a statement Monday. "With the approximately 70% survival rate, we consider this response extremely successful."

The organization said satellite tags show some surviving dolphins "swimming safely offshore," while whale watch vessels have reported seeing some of the dolphins, which were identified with temporary markings, swimming among "hundreds of other dolphins that were not involved in the stranding."

During their response to the stranding, IFAW said their mobile rescue clinic was damaged and will need repairs, and their supplies were exhausted. Nine of the dolphins were extracted and transported in the mobile rescue clinic to their release sites.

Cape Cod is a global stranding hotspot, with its unusual fishhook shape proving treacherous for marine mammals.

During the response to the stranding, on Tuesday, July 2, IFAW said 11 dolphins remaining in Wellfleet Harbor began swimming up Duck Creek, "a historic mass stranding location and a difficult spot to extract dolphins from." IFAW teams "herded" the dolphins to strand instead on a more accessible shore.

"By forcing them to strand in a controlled way, the team was able to extract them and transport them via our mobile dolphin rescue clinic," the organization said. Of the 11, only 9 were healthy enough to be released, and two were euthanized.

"Stranding, herding, and being caught in recurring tidal shifts is incredibly stressful for the dolphins," Katie Moore said in a statement. "The prognosis for each animal declines as time passes if they continue to re-strand. The animals are likely showing signs of the cumulative stresses and trauma associated with repeat strandings and effects of tidal fluctuations, even if they have not re-stranded."

—TMX contributed to this report.