Rescue Effort Hailed A Success After Over 100 Dolphins Rescued From Largest Single Mass Stranding Event In US History

Dolphins that two weeks ago were stranded in the mud of Cape Cod have now been seen swimming among other much larger groups out at sea, confirming the success of rescue efforts during the largest mass stranding of dolphins in US history.

During the first week of July, more than 150 people worked to save 146 dolphins that became stranded in shallow mud flats off Cape Cod, on the north-eastern tip of North America.

The rescue effort was led by the International Fund for Animal Welfare (IFAW) and with a survival rate higher than 70 percent – 37 deaths is significantly less than would be expected from such a high number of strandings over an extended period – the rescue effort has been deemed an outstanding success.

The first report on Friday June 28 was initially understood to be 10 Atlantic white-sided dolphins close to shore off the town of Wellfleet. As responders consisting of IFAW staff and volunteers arrived on scene, they identified many more animals. Sadly 10 dolphins had already died.

“We arrived to what appeared to be 80 to 100 dolphins on the shallow mud flats of Wellfleet’s Herring River ‘Gut’ – a global epicenter for mass strandings,” said Misty Niemeyer, stranding coordinator for IFAW. “We were able to provide supportive care, help those that were struggling, and keep them comfortable and ready for the incoming tide.”

A final review of data and imagery this week revealed there were actually 146 dolphins involved in the stranding.

The dolphins were herded in a highly coordinated response effort to encourage their movement back to deeper waters, first on foot and then switching to boating efforts as the water returned to high tide at 4:56pm. Two IFAW vessels and the Wellfleet Harbormaster continued their efforts until sunset at 8:15pm.

At first light Saturday morning, an IFAW team was back on the water to find 10 of the dolphins swimming in a dangerous area, however they were successfully herded towards deeper water. Surveillance continued all day and later in the afternoon IFAW received reports of large groups of dolphins, some tagged (meaning they were part of Friday’s group), swimming close to Brewster Beach in Cape Cod Bay.

On Sunday morning seven dolphins were back in shallow water in Wellfleet Harbour. One animal stranded was in such poor condition, it was humanely euthanised. This was not only important for the welfare of that animal, but also helps rescuers to be more successful in herding the remaining animals out. The very social nature of these dolphins means that they will stick together even in a bad situation. By removing individuals that are not well, the group may be more easily moved offshore.

That afternoon IFAW received reports that around 20 dolphins had stranded at Brewster, not far south of Wellfleet, and three had died. The remainder were successfully herded back to deeper water.

During Monday July 1, the team monitored the remaining dolphins in Wellfleet Harbour but as they had not moved on their own accord by Tuesday, the decision was made to herd the 11 dolphins toward shore to an accessible area.

“By forcing the animals to strand in a controlled way, where the team was stationed to extract them and admit them to Moby (IFAW’s custom-built mobile dolphin rescue clinic) we have the best opportunity to help the animals get out of the maze of the Wellfleet estuary and into deep water offshore,” Katie Moore, IFAW’s deputy vice president of Animal Rescue said.

Of the 11 animals, 9 were deemed healthy enough for release. Two were humanely euthanised. The remainder were transferred to Provincetown where they were released at a location that has direct access to open ocean and high likelihood of successful release.

Ms Moore said that after so many days, the animals are likely showing signs of the cumulative stresses associated with repeat strandings and effects of tidal fluctuations even if they have not re-stranded.

At that point the prognosis for any animal that might restrand had declined. Dealing with repeat tidal cycles is stressful for these pelagic dolphins. Most of the dolphins that are were stranding that day had stranded more than once, so the stress and physiological and physical trauma are compounding.

“While we are confident that the majority of the animals that were refloated on Friday have made it to deeper water, we have had reports of smaller groups close to shore each day. We have volunteers and colleagues from partner organisations proactively scouting the area. The team is exhausted but managing with the help of our partners and incredibly dedicated volunteers.

“We just hope the rest of the dolphins stay offshore now.”

There were no further strandings after July 2. Satellite tags are tracking several of these animals safely offshore, and those swimming with the larger groups that were seen by whale watch vessels were identified by their temporary markings.

The entire effort involved more than 150 people, including at least 25 IFAW staff, 100 trained volunteers, and additional assistance from AmeriCorps of Cape Cod, Whale and Dolphin Conservation, the New England Aquarium, the Center for Coastal Studies, and the Wellfleet Harbormaster.

Cape Cod is considered a global hotspot for live mass dolphin strandings. IFAW responds to an average of 268 strandings per year - this is why the organisation is considered a global expert and trains teams around the world. However this many dolphins in one event is the largest the organisation has seen.

It is still unclear why dolphins and whales strand. Dolphin and porpoise strandings on Cape Cod are driven primarily by the gently sloping sand flats, large tidal fluctuations, close proximity to productive feeding grounds, social nature of the species that strand, and the hook-like shape of the Cape itself. Many of the dolphins and porpoises that strand in this area have no clinically significant pre-existing diseases that cause them to strand.

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