Ecology and Conservation of the Leatherback Sea Turtle

Ecology and Conservation of the Leatherback Sea Turtle

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        Introduction

        An ancient creature, the leatherback turtle (Dermochelys coriacea) is an important asset to the viability of the ocean ecosystem. The declining population has hindered their role in maintaining a healthy marine ecosystem (Wilson, n.d.). This turtle is not only significant to the environment, but it is also significant to the study of science. It is unique amongst chelonians for having a soft shell rather than a hard shell; hence the name “leatherback” (Chen et al., 2015) Threats to the population vary and are powerful, all caused by humans. Through proper conservation efforts, the leatherback sea turtle population can be expected to rebound.

Biology and Ecology

        Dermochelys coriacea is a chelonian so genetically and biologically unique that it was placed in its own separate family for being so distinctive. The largest of all sea turtles, the leatherback has a unique skeletal morphology—instead of bony plates, this turtle has a slightly flexible carapace with a rubber-like texture. This unique soft-shell characteristic allows the turtle to dive up to depths of 1200 metres, or 4200 feet (Chen et al., 2015). The epidermis is black and scaleless, and the undersurface is a mosaic of pinkish-white and black. An adult leatherback can grow up to 2000 lb and 2.7m, while a hatchling is approximately two to three inches in length and weigh one and a half to two ounces (Pritchard, 1971). Leatherback sea turtle hatchlings are dorsally mostly black and show stripes of white along the flippers.

         The lifespan of this reptile is unknown; and is believed to have a similar lifespan to humans as some have been documented to live more than 50 years (“Leatherback Turtle”, n.d.). The core body temperature in adults has been recorded to be several degrees celsius above the ambient temperature (Chen et al., 2015). Their front flippers are proportionally longer than other sea turtles and lack claws or scales whereas the backflippers are paddle-shaped, making the turtle well-equipped for migrating extreme distances (“Leatherback Turtle”, n.d.).

        Leatherbacks have pointed tooth-like cusps that are designed for a soft-bodied pelagic diet—jellyfish, salps, etc.—instead of the common crushing chew plates other sea turtles possess. The mouth and throat have spines pointed towards the mouth to help retain the gelatinous prey (Pritchard, 1971). The leatherback can consume up to 440 pounds of jellyfish each day, and plays an important role as top jellyfish predator (Wilson, E.G. et al., n.d.).

                Female turtles remigrate back to the same nesting sites in intervals of 2-3 years, and lay an average of 80 fertilized eggs alongside 30 unfertilized eggs in each of their four to seven nests. The eggs intubate for approximately 65 days. Upon hatching, the juvenile sea turtles return to the ocean (Barragan et al., 2013).

        The leatherback sea turtle is a wide-ranging migratory turtle and is primarily found in the open ocean as far north as Alaska and as south as Africa. The total global population is estimated to only be 160,000 leatherbacks, and is divided into seven subpopulations, biologically and geographically different, located in the Atlantic, Pacific, and Indian Ocean (“Leatherback Turtle”, n.d.). Although the current populations of the Caribbean and Atlantic Ocean appear stable, the Western Pacific population has declined by more than 80 percent, and the Eastern Pacific population has declined more than 97 percent (Bell et al., 2004).

        Commonly found in the pelagic, the leatherback can also be found foraging in coastal waters. Juvenile and post-hatchling habitat requirements are virtually unknown, however, nest females prefer “high energy beaches with deep, unobstructed access” (“Leatherback Sea Turtle: Dermochelys Croiacea”, n.d.).

Threats

        The ocean biome is both one of the most resilient and the most vulnerable biomes on this planet. Many of the species in the oceans have been around for hundreds of millions of years.  The population is estimated to be around 160,000 leatherbacks. However, nesting populations of the turtle have declined by over 95% in the last 20 years; and tens of thousands of adult turtles die every year (Lewison et al., 2004). The main causes for these declines are accidental fishing capture, marine debris and pollution, environmental contamination, artificial lighting, loss or degradation of nesting habitats, and non-native vegetation.

        Leatherback sea turtles are most vulnerable to threats due to their late age of maturity, low reproductive rates, and high embryonic mortality rates (Bell et al., 2004). The average turtle matures at around 16 years of age and reproduces every two to three years (Pritchard, 1971; Barragan et al., 2013).

        The turtles can become entangled in gillnets, pound nets, and longline fishing gear. Nearly 3.8 million pelagic longline hooks are cast everyday, and approximately 48% of hooks caught turtles. Of that percentage, half of the turtles were leatherbacks (Lewison et al., 2004). Entangled turtles often drown and suffer serious injuries to their flippers. In addition to flipper injuries, longline gear can hook the leatherback in the jaw or esophagus (“Leatherback Turtle”, n.d.).  3,200 leatherback turtles are killed every year from pelagic longline fishing in the Pacific Ocean alone (Lewison et al., 2004).

        Marine debris and pollution are continuing problems for both sea turtles and their ecosystem. Every year, about 300 million tons of plastic is produced globally, only 10 percent is recycled, and an estimated seven million tons end up in sea (Wassener, 2011). Turtles in the pelagic environment commonly ingest these plastics or become entangled in them. Effects from the ingestion of plastics include, “blockage of gastric enzyme secretion, diminished feeding stimulus, lowered steroid hormone levels, delayed ovulation, and reproductive failure” (Derraik, 2002). Leatherbacks entangled in plastics may drown, have its ability to catch food impaired, or may incur wounds or cuts. This leads to a significant drop in fitness for the environment and ultimately poor survival rates.

        Environmental contamination can negatively impact nearshore habitats. Coastal runoff, marinas, aquaculture, oil and gas extraction, and boat traffic are some of the factors contributing to marine degradation (“Leatherback Turtle”, n.d.). Although how turtles function within the marine ecosystem is still poorly understood, global warming does have negative impacts on all aspects of the life cycle, as well as impact on the surrounding environment and prey.

        Threats in the terrestrial environment include loss or degradation of nesting habitats, beach armouring, artificial light, and non-native vegetation. Partial or total loss of nesting habitats can be the result of the erosion of nesting beaches. Rate of erosion is influenced mainly by sea level rise, which is an effect of climate change (Dudley et al., 2015). Human interference of coastal development and related activities results in accelerated rates of erosion, and also interrupts the turtles’ natural shoreline migration (“Leatherback Sea Turtle”, 2017).