Saving Cold-Stunned Sea Turtles
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New research could help optimize sea turtle search and rescue.
Wintry weather doesn’t just pose a risk to humans. Sea turtles can become “cold-stunned.” Organizations like the Network for Endangered Sea Turtles and the N.C. Aquarium on Roanoke Island have provided care for cold-stunned sea turtles in northeast North Carolina. Last year during the winter, staff and volunteers rescued nearly 800 turtles, breaking a 2016 record of 600.
Cold-stunning is a condition in which sea turtles become lethargic and are eventually unable to swim or eat. Wind and waves wash the lifeless bodies ashore.
As reptiles, sea turtles are not able to regulate their body temperature like humans. If temperatures remain low or turtles are not rescued, they will die.
Cold-stunning events in U.S. coastal areas on the Atlantic and Gulf of Mexico can affect thousands of sea turtles. However, understanding the effects of wind and water currents on the potential stranding locations of cold-stunned sea turtles would increase chances of successful recovery of the turtles before they die.
The Drifters
Biologists believe cold-stunning most often occurs in shallow bays and lagoons where water temperatures can fall quickly, as well as in areas with limited or obstructed access to warmer water due to the surrounding land. A team of scientists from the University of Rhode Island and NOAA chose Cape Cod Bay, surrounded by the hook-shaped peninsula of Cape Cod, Massachusetts, to study stranding “hotspots” — areas where strandings occur most frequently.
The research team used four types of drifters — floats that move horizontally with water currents — and outfitted each with a satellite transmitter to record its path. The design of two of those drifters uniquely mimicked the size and shape of sea turtles that typically experience cold-stun events; one drifter floated at the surface, and the other sank to the bottom, so researchers could examine the influence of deeper currents on the movements of cold-stunned sea turtles.
Six drifter deployments took place ahead of storm fronts when temperatures were expected to drop below the cold-stunning threshold.
The Hotspots
There were stark differences in the paths and stranding hotspots of the bottom turtle-style drifters and the surface turtle-style drifters.
When comparing the sea turtle-shaped drifter strandings to reported cold-stunned sea turtle strandings from the region’s Sea Turtle Stranding and Salvage Network, the researchers saw an overlap in the locations overall but not in hotspots that the drifters’ movements predicted.
Turtle-style bottom drifters took roughly 10 times as long to strand, providing clues as to the timing and condition of cold-stunned sea turtles. It appears free-drifting, cold-stun turtles will be transported to different regions of the coast depending on the depth of water at the point of their cold-stunning.
Rescue volunteers have witnessed cold-stunned sea turtles stranding in pulses following cold fronts. Earlier waves arrive with most turtles alive versus later pulses, which arrive with most turtles deceased. The findings from this study suggest that the turtles that strand later could have been submerged at the time of their cold-stunning.
In addition, the sea-turtle-shaped surface drifter behaved differently from the traditional drifters scientists have used to study currents and sea turtle stranding locations. Traditional drifters are not representative of sea turtle size and shape and do not assess how bottom currents affect stranding locations.
more on turtles and other sea life
Sara Mirabilio is a fisheries extension specialist with North Carolina Sea Grant and co-curator with Scott Baker of the award-winning Hook, Line & Science series, which published an earlier version of this story. Visit HookLineScience.com.
