It’s remarkable that a turtle can grow big enough to outweigh a rhino. It’s even more impressive that the leatherback does it feeding exclusively on jellyfish and other jelly animals, but they eat a lot of jellies — adults consume between 800 and 900 pounds of them every day, on average. Leatherbacks are the ocean’s major jellyfish predator, which is why they’re considered a keystone species. Without leatherbacks to control their numbers, jellyfish populations could grow, unchecked, and negatively impact the marine food web.
Now, jellies are a rather slippery meal and they don’t stay down too easily. To stop them from sliding right back out of their mouths, leatherbacks have hundreds of long, downward-facing spines lining their mouths and throats. It’s an evolutionary advantage that’s worked for hundreds of millions of years. Yet, in less than 100 years, our plastic waste has transformed it into a potentially fatal vulnerability.
In the dark and sometimes murky waters of the ocean, plastic bags, wrappers, balloons, and other debris can look or taste a lot like jellyfish. And just like jellyfish, leatherbacks can’t regurgitate plastic once they’ve ingested it. The plastic becomes impacted in their gastrointestinal tract and causes partial or complete blockages or injuries that can lead to decreased digestive efficiency and chronic infections. It can also have energetic and reproductive costs. For some leatherbacks, ingesting plastic leads to starvation and, ultimately, death.
While the leatherback can hold its breath longer and dive deeper than any other sea turtle (85 minutes at depths of up to 4,200 feet!), it’s still an air-breathing reptile that will drown if it’s unable to surface. And that’s often what happens when leatherbacks become tangled in our marine debris.
Lost and abandoned fishing gear are death traps in the open ocean. In the global fishing industry, trawls, longlines, driftnets, purse seines, and traps are largely responsible for the incidental capture or entanglement of leatherbacks. Longlines, as an example, are tens of miles long and contain thousands of baited hooks. Leatherbacks are often attracted by the bait and either get hooked or become tangled in the line and drown. Even if they’re hauled up alive, they can sustain injuries during their capture and release that eventually kill them.
Boat strikes can also cause blunt force trauma and cuts that can critically injure or kill. Leatherbacks are often hit when they come to the surface to breathe or while they’re feeding or mating in shallow areas. Turtles that do survive are often covered in scars.
When it comes time for females to lay their eggs, they return to their native nesting beach, dig a hole in the sand, and deposit around 80 eggs. Each female makes several nests in a season, which means hundreds of eggs are left to incubate unattended. Leatherbacks must lay so many eggs because so few hatchlings survive into adulthood; only an estimated one in one thousand survive.
The incubation temperature inside the nest determines whether the hatchlings are male or female. A mix of males and females occurs when the nest temperature is approximately 82-85℉. Higher temperatures produce more females while lower temperatures produce more males.
Rising global temperatures associated with climate change are an enormous concern for leatherback researchers, who have seen an increase in mostly female nests. A disproportionate number of female hatchlings can have a disastrous impact on the species’ ability to reproduce and recover their population.
Leatherbacks migrate further than any other sea turtle species as they travel between their temperate feeding and subtropical breeding grounds. Females require sloping, sandy, undisturbed beaches backed by vegetation for nesting. Most of them migrate to the same region, and even the same nesting beaches, every two to three years.
However, rising sea levels associated with climate change, increased coastal development, and coastal marine debris often mean their nesting sites are degraded or have disappeared altogether by the time they mature and return.
You may have heard that moonlight reflecting on the water guides sea turtle hatchlings back to the sea, but that’s an old wives’ tale. Hatchlings find their way to the ocean by drawing away from the tall, dark silhouettes of sand dunes and toward the lower open horizon of the ocean.
But that doesn’t mean artificial lights from coastal communities don’t cause problems. Just like moths that are hopelessly attracted to porch lights, turtles can also become “light trapped.” Artificial lights can disorient nest mothers and misdirect hatchlings. When hatchlings crawl away from the ocean, they’re easily picked off by predators.
Coastal development also alters the coastline by diminishing or removing the vegetation around it, which can lead to erosion and the loss of crucial nesting beaches. While beach armoring can help prevent erosion, the fortifications often create a barrier for females attempting to return to their nesting beach. Sometimes, they actually lead to further erosion. Mechanical raking of developed beaches can compact the sand and affect the ability of hatchlings to emerge.
Alone or together, these changes can reduce the quality of nesting beaches and impact sex ratios, which has a negative impact on their population long term.
Sea turtles are heavily protected in several countries, including the US. Harvesting and consuming sea turtles are often illegal. However, sea turtles are a food source in some indigenous coastal communities, especially those in Central America, Oceana, and Asia. Some cultures consider their meat a delicacy while others believe their eggs are aphrodisiacs. While the most commonly eaten sea turtle is the green turtle, leatherbacks and other species are also hunted and eaten by humans.
During nesting season, hunters will seek females that have returned to shore to nest; if the eggs are also prized, they’ll wait until she’s laid her eggs before they kill her. This harvesting has a devastating and unsustainable impact because it destroys both present and future generations of leatherbacks. The critically endangered Pacific population has all but collapsed because of these harvests. Education about the importance of conserving these animals is a crucial part of changing this behavior.
Marine biologists at Florida Atlantic University® are respected for their research in marine conservation, physiology and behavior, sensory biology of marine vertebrates (particularly sea turtles and fishes) and invertebrates and for coastal ecology and nutrient cycling.
The Leatherback Sea Turtle Bracelet was released June 2019 in partnership with Florida Atlantic University® and is no longer available at this time.
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