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Why have frozen sharks been washing up on the Cape?

It’s an alarming sight that has drawn national media coverage: frozen shark carcasses washing up on Cape Cod beaches during the recent cold snap.

But state shark expert Greg Skomal said the thresher sharks like the four that have been found dead in Wellfleet and Orleans in recent days probably aren’t literally freezing to death. The ocean predators likely are getting stranded in shallow waters in Cape Cod Bay while attempting to swim to warmer southern waters, he said.

“The rapid cooling associated with this cold snap and water temps is forcing the sharks to move south at a faster pace, and the landmass of Cape Cod is contributing to them getting stranded in shallow water,” said Skomal, the senior fisheries scientist for the state Department of Fish and Game, adding that the exact cause of the sharks’ deaths remains hypothetical at this time.


The Cape, shaped like an outstretched arm that hooks at Provincetown, can act as a natural trap for animals trying to move south quickly, and most shark species need to be continually moving in order to breathe effectively, he said. “So if it gets caught up on a sandbar, it’s probably going to drown, literally, because it can’t breathe effectively,” said Skomal, who leads the Massachusetts Shark Research program.

Water temperature may play a role at some point in the animal’s death, but he stressed the real factor would be that the shark is stranded and, therefore, incapable of breathing.

The Atlantic White Shark Conservancy, which assists Skomal and his colleagues studying sharks, responded to the strandings of two thresher sharks in Wellfleet and Orleans on Dec. 27 and a third was found in Brewster two days later. “We hauled the shark off the beach and it is currently thawing at NOAA Fisheries Service to be dissected later,” the conservancy wrote on Facebook of the shark in Brewster. “A true sharkcicle!”


The conservancy said a fourth thresher shark was found in an ice pack off Wellfleet on New Year’s Eve.

Skomal said thresher sharks are a “relatively poorly studied species” when it comes to their movement patterns and their exact temperature requirements in the water. But it is known that the sharks migrate north during the summer months and return to the southeastern coast of the United States or the Gulf of Mexico during the cold seasons.

“The sharks that we’re seeing on Cape Cod are likely late migrants,” he said. “In other words, they remained in the Gulf of Maine and were probably slowly making their way south as is typical of these sharks.”

Skomal said it’s unclear how many sharks may still be trying to make their way past the Cape to warmer waters as another blast of Arctic air approaches this weekend on the heels of a major winter storm.

The scientist said he and his colleagues are on the lookout year round for stranded sharks. And they have seen what they call “late season threshers” getting stranded on Cape Cod beaches in past winters. But the number that has been seen this year is not typical.

He encouraged anyone who spots a stranded shark in the coming days to reach out to the shark research program or the Atlantic White Shark Conservancy, which is currently running a donation drive for equipment to respond to shark strandings.


Contact Dialynn at dialynn.dwyer@globe.com