Why are so many sea turtles being stranded in Cape Cod?

By Dana Kobilinsky

Greater numbers of Kemp’s ridley sea turtles are showing up cold-stunned and stranded on Cape Cod Bay. ©Jereme Phillips, USFWS

It’s not unusual for sea turtles to turn up cold-stunned and stranded on Cape Cod beaches. As they migrate south from the Gulf of Maine to the Gulf of Mexico at the onset of fall, cold waters can lead to hypothermia, causing them to wash ashore, alive but dazed. But far more sea turtles have been affected in recent years, leaving researchers to wonder why.

In the 1970s and ’80s, the number of cold-stunned Kemp’s ridley sea turtles (Lepidochelys kempii) was in the double digits. By 2014, the number reached over 1,100. To find an explanation, researchers developed a model to test what factors might be behind the dramatic increase.

“Cape Cod is sort of shaped like a hook and is the perfect turtle catcher for turtles migrating south if they get stuck,” said Lucas Griffin, lead author of the study and a PhD candidate at the University of Massachusetts Amherst. After they wash up on the shore, volunteers take them to the New England Aquarium to rehabilitate them and then fly them south to release them back into the water, he said.

In the study published in PLOS ONE, Griffin and his colleagues created a mathematical model to assess environmental variables including surface temperature, atmospheric variables and numbers of hatchlings. They tested which of these factors were the most important in explaining higher cold-stunning events.

“Essentially, what we found was, at least with our models, population growth was not an important factor for cold-stunning events,” he said. “It’s alternatively linked with warmer late summers and falls.”

Warmer waters may have allowed more turtles to shift north in their distribution, Griffin said, or juvenile turtles may be staying north longer and migrating later, allowing the turtles to get to get stuck in the bay when it gets cold.

The Gulf of Maine is warming faster than 99 percent of the world’s oceans, Griffin said. Using their model, he and his team predicted future temperatures out to 2031 and found that as many as 2,300 turtles could end up cold-stunned and stranded each year. “As Gulf of Maine temperatures continue to increase, we expect more cold stunned turtles to become stranded along Cape Cod beaches,” he said

Griffin suggests continuing rehabilitation for the ones that wash up cold-stunned. “We argue that it’s really important to rehabilitate and spend the money because they add in resiliency for populations still recovering,” he said. While nesting numbers for the endangered turtle have increased dramatically since the 1970s, in recent years they have leveled off with no definitive explanation, Griffin said.

“We really need to make sure we’re saving every turtle we can to build in resiliency,” he said.

Dana KobilinskyDana Kobilinsky is associate editor at The Wildlife Society. Contact her at dkobilinsky@wildlife.org with any questions or comments about her article. You can follow her on Twitter at @DanaKobi.

Read more of Dana's articles here.


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