String of thresher shark strandings on Cape Cod could be related to deep freeze

The stubborn Arctic cold that in the northeastern part of the country has been linked to 17 deaths and forced Niagra Falls to partially freeze over may also be responsible for a rash of shark strandings along Cape Cod.

Over the last week, four thresher sharks were found dead and frozen after becoming stranded along several beaches.

Experts with the Cape Cod-based Atlantic White Shark Conservancy, an organization that works to increase knowledge and perception of Atlantic great white sharks, responded to strandings on Dec. 27 and Dec. 29. The most recent shark discovery came on New Year's Eve near the town of Wellfleet.

The sharks were later transferred to the National Oceanic and Atmospheric Administration’s (NOAA) Fisheries Service to be examined further.

Shark strandings during the winter along Cape Cod are not unusual. However, what is uncommon is the number of strandings in the last week, according to Gregory Skomal, a senior marine fisheries scientist for the Massachusetts Division of Marine Fisheries.

While the preferred temperature ranges of the common thresher shark are not well defined, researchers do know that thresher sharks typically move into northern latitudes, such as around Cape Cod and the Gulf of Maine during the summer months and into the fall.

Skomal explained that as is typical of other species, the sharks will migrate south as water temperatures drop in the winter.

In the case of these thresher sharks that remained in northern waters, he said that it’s possible that changing water temperature associated with the recent deep freeze forced these sharks to begin to migrate south abruptly.

However, due the unique landscape of Cape Cod, it likely acted as a trap and stopped the sharks' southward movement when they entered the shallow waters of Cape Cod Bay.

“They move south rapidly in response to the changing water temperature because they don’t want to be in super cold water,” Skomal said. “If you look at Cape Cod, it’s kind of a natural trap area; it’s shaped like a human arm extending to the north.”

Any shark or migrating animal that encounters that land mass is likely to get trapped in there if they can’t get around the cape, which these sharks didn’t, he added.

Once the sharks thawed, a necropsy was expected to be performed on collected tissues and organs by state and federal officials to produce more insight about why the sharks ended up on the beaches.

Strandings that happen in the summer or fall in New England can involve great white sharks or basking sharks that may get too close to shore and stuck on sandbars while hunting for food. Winter strandings are more attributed to sharks moving south and getting trapped in shallow waters.

Cold shock can impact marine species such as sea turtles, which breathe air and can also become stranded. However, it's more likely the sharks died after getting stranded as opposed to freezing to death in the water, according to Skomal.

While it's possible sharks could suffer from hypothermia or cold shock, it can be very hard to prove, Skomal said. The bigger problem for them is struggling to swim in shallow water and losing the ability to breathe after getting stuck on land.

"It's tough to demonstrate hypothermia in these fish," Skomal said.

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