By Jonny Lupsha, Wondrium Staff Writer
Sea turtles that migrate from Indonesia to California are declining. Leatherbacks swim 7,000 miles and have been studied for 40 years, but their numbers have slipped by an estimated 80%. There are seven species of sea turtles.
A species of sea turtles that dates back to the dinosaurs seems to be in decline. Leatherbacks are known for hatching on beaches in Indonesia and Papua New Guinea and migrating 7,000 miles across the Pacific Ocean to the West Coast of the United States. They then eat a vast amount of jellyfish and turn back the way they came, returning home.
In the last 30 years alone, their numbers have dropped by 80%. Scientists believe their possible extinction is being brought on by international fishing, the destruction of their nesting grounds, and climate change.
In his video series Life in the World’s Oceans, Dr. Sean K. Todd, the Steven K. Katona Chair in Marine Sciences at the College of the Atlantic in Bar Harbor, Maine, said that leatherbacks are so different from other sea turtles that they’re in their own biological family.
The Leatherback Exception
According to Dr. Todd, there are seven species of sea turtles: the leatherback, the Kemp’s ridley, the olive ridley, the the loggerhead, the hawksbill, the green, and the flatback turtle. Aside from the leatherback, all are ectothermic, or cold-blooded, which comes with its own pros and cons.
“On the plus side, sea turtles do not need to invest energy in staying warm; their physiology is adapted so that they can operate metabolically at the typically low temperatures of the ocean,” he said. “The main disadvantage to being ectothermic is that because the surrounding environment is relatively cold, the the internal temperature of sea turtles is also cold, and this limits their metabolism.”
However, leatherbacks are the exception. Like humans, leatherbacks are endothermic, meaning they maintain their body heat internally. In fact, he said, this difference is so important that leatherbacks, which are also the largest of the sea turtles, are classified in their own family, Dermochelyidae.
“This is doubtless why leatherbacks have the highest latitude distribution of all the sea turtles,” Dr. Todd said. “For example, they are common in my neck of the woods up in the Gulf of Maine and I have seen them as far up as the subpolar waters of Newfoundland and Labrador.”
A Surprising Adversary
Although climate change is most often blamed for declining marine populations, and it does play a role in the disappearance of the leatherbacks, it’s not the most urgent cause of the sea turtle decline.
“Perhaps the most insidious impact we are having on turtle populations is on their nesting habitat,” Dr. Todd said. “Sea turtles must come to shore to lay their eggs, burying them in nests less than a meter deep on a sandy beach, away from predators such as birds, coyotes, and foxes.
“However, humans like sandy beaches too, and so often compete for the same habitat.”
Dr. Todd cited noisy condominiums and hotels with bright lights as things that may scare turtles off from nesting at beaches. Or, if a desperate female lays her eggs there, the hatchlings may be more attracted to the bright lights and big sounds humans make than to the ocean. This can expose them to dangers like seabirds and land predators as opposed to the relative safety of the open ocean.
Threats to sea turtles are compounded by how little we know about them, owing to their lives in the sea. Leatherbacks may be gone for good before we can ever truly understand them.