Notes from the Field
Every Turtle Counts
Every fall on Cape Cod endangered sea turtles become cold stunned and wash up on Cape beaches. Thanks to the Audubon’s Wellfleet Bay Wildlife Sanctuary and a cadre of dedicated volunteers many of these turtles are rescued, rehabilitated and released back into the wild. For the last few years, local high school students have been studying the tides and currents in Cape Cod Bay to help researchers better understand where cold stunned sea turtles are most likely to wash up. Students build and deploy devices called drifters that drift with the tides and currents similar to cold stunned sea turtles. The drifters are equipped with GPS units that allow the students to follow the drifter tracks in real time. Students can compare where the drifters finally wash up on the beach to where cold stunned sea turtles are found.
When you think of Cape Cod, you might think of sand dunes, salt marshes, and big ocean beaches. You might not think of sea turtles. But every summer several species of rare and endangered sea turtles come to Cape Cod to enjoy the warm water and abundant food supply. When the fall arrives these tropical creatures head back south to warmer waters. Well, most of them do. Turtles feeding in Cape Cod Bay are in danger of becoming trapped by the Cape’s geography. Cape Cod sticks out about 65 miles into the Atlantic Ocean in an east west direction. This forms a barrier for turtles that are trying to head south from Cape Cod Bay.
Sea turtles are ectothermic, which means their body temperature is the same as the environment. When the water falls below 50 degrees Fahrenheit the bodies of the sea turtles start to shut down. They cannot swim anymore, so wind, tides, and currents push them around. Eventually, many of them are washed up on Cape Cod Bay beaches. The most critical time for cold stunned sea turtles is from November to the end of December. During these months volunteers walk the beaches at every high tide looking for stranded sea turtles. The air temperature at this time of year is much colder than the water. Turtles left on the beach die very quickly. If the turtles are found soon enough, they can be rescued, rehabilitated and released back into the wild.
Kemp’s Ridley sea turtle stranded on an Eastham, MA beach. (photo courtesy
of Wellfleet Bay Wildlife Sanctuary)
The most common sea turtle to strand is the Kemp’s Ridley sea turtle (Lepidochelys kempi). In the 1940’s there were estimated to be over 100,000 of these turtles. Today there are about 10,000. In 2014 over 1,000 Kemp’s Ridley sea turtles were rescued on Cape Cod. Each one of these highly endangered turtles that safely makes it back into the wild may contribute to increasing the population.
Quickly finding stranded sea turtles is key to their survival. There are about 80 miles of shoreline along Cape Cod Bay and a limited number of volunteers to walk its beaches. How do the turtle rescuers know what beaches to walk? Audubon relies on experience to guide how they deploy their volunteers. There are beaches where turtles are historically found. We also know that certain wind conditions favor some beaches for strandings. But what if we could collect data on the local wind, current and tide conditions to help more accurately know where turtles are likely to strand? To this end, Wellfleet Audubon, GOMI, and local high school students embarked on a research project to do just that called “The Drifter project.”
James Manning, a researcher from NOAA, had been working with students and GOMI for several years building and deploying ocean drifters all along the Gulf of Maine, of which Cape Cod Bay is a part. Students from two local Cape Cod high schools, Nauset Regional High School and Monomoy Regional High School, and Audubon staff started building and deploying drifters off the beaches of Cape Cod Bay during sea turtle stranding season. Drifters mimic the movements of cold stunned sea turtles by being pushed through the water by wind, waves, and tides. Each drifter has a GPS unit on it, so its movements are observed in real time. Eventually, the drifters are washed up on Cape Cod Bay beaches just like sea turtles. We hope that the drifter d