The Leatherback Sea Turtle
The most unique of all sea turtle species
The leatherback sea turtle is the most unique of all sea turtle species. They have the largest thermal and geographic ranges out of any reptile in the entire world. The leatherback is also the largest reptile by weight. There is fossil evidence to suggest that this species has remained majorly unchanged for over 110 million years! They have survived the time of the dinosaurs and are only now facing extirpation from different ocean basins due to extreme and long-term pressures caused by the human race.
The leatherback sea turtle is the only sea turtle species that does not have a hard, bony carapace made of keratin. Their teardrop-shaped carapace is made of cartilage and has seven ridges, a body design that makes them very hydrodynamic in the water. It is thought that leatherbacks reach sexual maturity anywhere between nine and twenty-two years of age, when they come back to the beach on which they were born to lay their first clutch of eggs. Leatherbacks do not have claws, as do all other sea turtle species. They often travel as far as 35km per day as part of their cyclic oceanic migrations. The deepest dive ever recorded was to about 4,000 feet, which is deeper than some whale species dive.
Leatherback conservation is particularly important because leatherbacks are a keystone species. Leatherbacks feed only on jellyfish species like gelatinous zooplankton, moon jellies, and sea nettles, which are opportunistic predators that consume juvenile fish species and fish larvae. Leatherbacks have special papillae in their throat to assist with swallowing their slippery prey. Able to eat their weight per day, they help to regulate jellyfish populations. By protecting leatherbacks, we can therefore naturally regulate jellyfish populations, support the recovery of fish stocks and subsequently contribute to international food security.
Leatherbacks have been referred to as a polar reptile. They have a remarkable layer of insulating fat. They are not warm- or cold-blooded but exhibit something that has been termed Gigantothermy. Gigantothermy is thought to be a body life history characteristic exhibited by polar bears, panda bears, and even dinosaurs. One of the mechanisms observed in their physiology is something called counter-current heat exchange, which occurs when veins carrying oxygen-poor, cooler blood heading back to the heart, and arteries carrying oxygen-rich warmer blood coming from the heart, are located close to each other. This arrangement allows heat to be conserved in the extremities. When leatherbacks dive, they can withstand temperature differences that other sea turtles cannot and are therefore found at latitudes that none of the other more tropical sea turtles can be found at. Other sea turtle species are ectotherms, meaning they use the environment to regulate their body temperature. In leatherback sea turtles, when they are overheated, their skin turns a pinkish color as they flush blood to the outside of their body in an effort to cool down. The body temperature of individuals measured off the coast of California is typically six to seven degrees higher than the temperature of the ambient environment, providing further evidence that this species is able to regulate the temperature of its body to utilise foraging habitats at latitudes where jellyfish can be found and where no other marine turtle species can thrive.
There are a few constraints of being a sea turtle: you must breathe air, you must lay your eggs on land, and you must spend the majority of your life in the ocean. This use of both oceanic and terrestrial habitat presents unique and expansive conservation challenges for sea turtles in general, but specifically for leatherbacks. Leatherbacks do not occupy nearshore foraging habitats during their developmental period like other sea turtles but spend all of their developmental life stages as a pelagic species, occupying the open ocean. This behaviour makes protecting them from fishing efforts even more of a challenge. Oftentimes already protected reefs and seagrass beds do not provide protection for this species, and we know very little about their movements across life stages in the open ocean.
Leatherbacks are symbolic as a flagship species. They are affected by almost all of the greatest threats facing our ocean today including climate change, plastic pollution, unsustainable fisheries bycatch, and also threats facing coastal habitats such as sea level rise, beach erosion, temperature increases and ocean acidification. They exemplify and put a charismatic face to these issues. Plastic bags floating in the water column resemble the leatherback’s primary prey, and leatherbacks have the lowest natural nest hatching success rate of all sea turtle species, which is only decreasing with observed global increases in nest temperatures. Leatherbacks are one of the species of sea turtles that do not nest close to or behind the vegetation line, making their nests more susceptible to rising tides and beach erosion. By studying leatherback sea turtles and the threats facing their survival, we can open the doors to conversations about the biggest threats facing our oceans today.