The Leatherback: An Ancient Giant on the Brink

The evolutionary lineage of leatherbacks has been the topic of much debate amongst scientists [1]. It's a species distinguished from other sea turtles by the strange nature of its skeletal structure, partially endothermic body temperature, and highly unusual external features, namely the leather-like "shell" for which it was named [2]. However to call it a shell would be a mistake, instead its carapace is covered by skin and oil flesh making it very hydrodynamic [2]. Leatherbacks have existed for about 100 millions years, however they are the last species left in their family (dermochelyidae), others of its kind went extinct around 50 million years ago making it the largest sea turtle alive today [1]. Adults average about 1.3-2.7 meters (4-9 feet) and 300-500 kg (660-1100 lbs) [2]. The largest ever measured in at 916 kg (2019 lbs) and 3.1 meters (10 ft) [2].

Feeding Habits [3]

The leatherback sea turtle (dermochelys coriacea) is thought to spend the most of its time in the open ocean making it the most pelagic of all the sea turtles. Yet in spite of this, they forage close to shore and over continental shelves. The distribution of leatherbacks generally depends heavily on the distribution of their food sources – jellyfish and other gelatinous organisms. These creatures that leatherbacks depend on tend to accumulate near convergent zones or water mass boundaries from the surface to great depths. Thus leatherbacks can be found throughout the water column, some having been found at depths of 1.2 kilometers.

The exact eating habits of most sea turtles are not well understood, however for leatherbacks, the prevailing theory is that they specialize in gelatinous species. This line of thought has developed through the stomach contents of the animals which almost always is composed of jellyfish, with the occasional shrimp or small crustaceans.

Migratory Behavior

Hatchling sea turtles undertake amazingly long-distance migrations to reach offshore nursery areas. Upon entering the ocean many species, of which the leatherback is one, undergo a period of hyperactive swimming in which they may swim for the entirety of their first day and night [3]. Unlike most reptiles they can sustain vigorous activity for extended periods of time [3].

As adults, leatherbacks have the widest migratory range, swimming to the highest latitudes and furthest longitudes of any sea turtle species [2]. A feat which is largely aided by their endothermic ability to maintain high body temperatures.

Map of Pacific Leatherback Sea Turtles Migration:

Leatherbacks in the pacific typically travel from tropical nesting beaches in the western pacific to areas rich in food in the northeastern pacific. Making this 11000 km journey takes roughly 10-12 months [2].

Listing Under the Endangered Species Act (ESA)

The leatherback is currently listed as endangered (seriously at risk of extinction) throughout its range and was first protected under the ESA on June 2 1970, however the most recent recovery plan for the United States was established in January of 1998 [4].

Changes in Distribution

In 1982 the global population of leatherbacks was estimated to be 115,000 adult females. However by 1996 that number had been driven down to around 30-40,000. The Pacific population has been hit the hardest. One nesting site, which in 1968 had seen more then 3,000 females had, by 1993, been reduced to just 20. But, as the species which spends most of its time in the vastness of the open ocean, the specific changes in range and distribution of the animals are difficult to determine when they are not nesting.

Thankfully though, not all populations of leatherbacks have declined. Those in the Atlantic, though impacted have faired much better. In southern Africa three decades of firmly enforced protection of have quadrupled the size of some small nesting sites.

How Did It Come To This?

The recovery plan described for leatherbacks states that the threats are varied and change from place to place. Various island groups have been evaluated individually to determine a total of 22 separate dangers. The primary threats to the animal's continued survival remain incidental capture by coastal and Open Ocean fishing operations, and the killing of nesting females on the beaches. More specific problem range from light pollution in which hatchling lose their sense of direction on their way to the ocean, all the way to entanglement in or ingestion of debris (plastic bags pose a serious threat due to their similar appearance to jellyfish in the water).

Why Do They Matter To Us?

Aside from the intrinsic value of retaining such an ancient and majestic animal, many commercially lucrative fish species have been impacted by unusually high numbers of jellyfish [5]. Since leatherbacks are a natural predator of jellyfish, they play a critical role in controlling their populations, and thus maintaining fishing industries around the world [6].

What Must We Do To Help?

Ultimately, the hope is to delist leatherbacks from protection under the ESA however, the number of solutions matches the number of problems the animals face. To see that the animal recovers [4]:

1. Incidental take by fisheries must be eliminated
2. The United States must support efforts to protect nesting sites, eggs, and females.
3. Determine population size and movement patterns in foraging areas (like those in the U.S.) to determine further threats.
4. Identify stock home ranges using DNA

What Can You Do To Help?

One of the most transformative experiences I ever had in high school came when my class was given the opportunity to go to Costa Rica to aid with conservation efforts for sea turtles. We stayed in a small town where, during the day where we relaxed and helped locals make additions to their hatchery, but at night we ventured out on to the beach to collect the eggs of laying females so that the eggs could be monitored until they hatched. All of the turtles I saw were green sea turtles, save the one leatherback that came ashore to lay her eggs, which was an absolutely incredible sight. I highly recommend this excursion for your next vacation. But on the day to day, simply ensuring that your used plastic bags end up where they belong (in the trash), might be enough to save the life of a sea turtle.

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Works Cited

1.
Kennedy, Jennifer. "How Did the Leatherback Sea Turtle Evolve?" About.com Education. N.p., n.d. Web. 03 Dec. 2015.

2.
"Leatherback Turtle (Dermochelys Coriacea)." :: NOAA Fisheries. National Oceanic and Atmospheric Administration, 11 June 2015. Web. 04 Dec. 2015

3.
"Recovery Plan for U.S. Pacific Populations of the Leatherback Turtle (Dermochelys Coriacea) /." (1998): n. pag. Recovery Plan for U.S. Pacific Populations of the U.S. Department of Commerce National Oceanic and Atmospheric Administration National Marine Fisheries Service U.S. Department of the Interior U.S. Fish and Wildlife Service Leatherback Turtle. Pacific Sea Turtle Recovery Team. Web.

4.
Musick, John A. "The Biology of Sea Turtles." Ed. Peter L. Lutz. CRC Press, 1997. Web. 3 Dec. 2015.

5.
"Jellyfish Taking over Oceans, Experts Warn - CNN.com." CNN. Cable News Network, n.d. Web. 04 Dec. 2015.

6.
"Rising Jellyfish Populations: Can Leatherback Sea Turtles Come to the Rescue?" Rising Jellyfish Populations: Can Leatherback Sea Turtles Come to the Rescue? N.p., n.d. Web. 04 Dec. 2015.