On the heels of an unusually high number of sea turtle strandings on Cape Cod in late November, Riverhead Foundation staff are bracing for a similar episode here on Long Island this month. The cause of the strandings is “cold-stunning,” a condition not unlike hypothermia among humans, that is prompted by a drop in water temperature in our shallow bays into the low 50-degree range.Sea turtles, being cold-blooded, cannot regulate their internal body temperature by generating heat, as mammals and birds can. A notable exception to this rule among turtles is the leatherback (Dermochelys coriacea), which can generate internal heat by metabolizing stored reserves of brown fat and maintain an internal body temperature that is as much as 32 degrees warmer than the ambient sea water. This, and several other characteristics of this fascinating creature, enables the leatherback to range as far north as Newfoundland.
The bottom line among the sea turtles is that once their body temperature drops below 55 degrees, a threshold for maintaining normal systemic function is crossed. Digestion fails, as key enzymes are not produced, and feeding ceases. The heart rate drops to as low as two or three beats per minute. Respiration may not be detectable. And, of course, swimming ability is seriously impaired.
Cold-stunned turtles will float, but they are at the mercy of currents generated by wind and tide, and cannot make their way offshore and south to warmer water.
Western Atlantic sea turtles nest on beaches in the tropics and southeastern United States. Hatchlings make their way out to sea, spending their first years of life as pelagic surface feeders. My references mention this last aspect of their life history as a hypothesis, and I’m not sure if that has been since proven.
Once they reach a carapace size of 8 to 12 inches, the juvenile sea turtles move to inshore waters to feed on organisms in the benthic community: mostly crabs, mollusks, eelgrass and algae.
In the late 1980s, biologists documented the use of northern estuaries in the Long Island and Cape Cod region by juvenile green, loggerhead and Kemp’s ridley sea turtles. These turtles (8 to 18 inches in length for the green and ridleys turtles, and 12 to 20 inches long for loggerheads) would arrive in June and remain active in our area through the summer and early autumn, exhibiting high growth rates during that time.
In October, when the water temperature in the shallow estuaries declines and cools rapidly, these turtles begin moving offshore into the warmer ocean. By late November, the water temperature in the estuaries drops into the low 50s, and we begin to see cold-stunned sea turtles on our bay beaches.
It is not clear why some sea turtles do not leave the area before water temperatures drop to that critical point and their swimming ability becomes impaired. But this past week, the number of sea turtles—mostly the federally endangered Kemp’s ridley—found cold-stunned and stranded on New England beaches was double that of the previous record high set in 2012.
Long Island’s cold-stun season lags a week or two behind New England’s. And cold-stunning is not a problem solely confined to the north. An unusually cold spell in 2010 resulted in a cold-stun episode among sea turtles in Florida, and a cold snap this fall dropped water temperatures on the Texas coast below the mid-50s threshold, impacting sea turtles in that region.
The Riverhead Foundation relies heavily on volunteers to patrol bay beaches over the next two weeks in search of cold-stunned turtles. There are only a thousand mature female Kemp’s ridley turtles in the world. Reaching 100 pounds and 2 feet (shell length), these females can reach 50 years of age. Sea turtle eggs and hatchlings have very low survival rates, but have few predators once they are several years old. Saving a few juveniles that are cold-stunned can make a difference.
The best time to check your bay beach for cold-stunned sea turtles is after high tide and when the wind has been blowing toward shore. If you find a sea turtle on the beach, call Riverhead Foundation’s hotline immediately: (631) 369-9829. Although the turtle may appear to be dead, unless there are obvious signs of decomposition, assume it is alive. Most stranded turtles will not survive a night on the beach when air temperatures drop below 50 degrees, so contacting the hotline is important.
The treatment for these turtles is complicated: rewarming must be done slowly, at a rate of 5 degrees per day. Trained staff will check and treat for frostbite, dehydration and infection (cold-stunning depresses the immune system), and administer protective lubricants on the skin and eyes.
This is a wildlife conservation issue in which volunteers can make a huge difference. Please consider getting involved.