Leatherback turtles are huge!

The largest sea turtle on Earth

Shell length: 132 -198 cm

Mass: 250 – 1000 kg

Colour: Black with white patches on top (carapace). White with black patches underneath (plastron)

Habitat

These open water giants have habitats that range from New Zealand to Great Britain and are sometime found in subarctic waters. There are four main populations of leatherback turtles. Those that nest in the Atlantic beaches of the Caribbean and South America, those that nest in Gabon in West Africa, those that nest on the Pacific beaches of Mexico and Costa Rica and those found nesting across the Pacific in the South East Asian beaches of Thailand Papua New Guinea and Malaysia. The Atlantic turtles travel to the Gulf of Mexico and on to the Atlantic Ocean. Turtles on the Pacific Coast of Mexico and Costa Rica travel south to Peru and Chile and then on to the Galapagos Islands. And those nesting in Papua New Guinea swim across the North Pacific to feeding grounds off the coast of California. Despite these turtles habiting different regions, there is still mating between the different populations because the occasionally swim between the India and Atlantic Oceans.

Behaviour

Unlike other sea turtles, it is believed that Leatherbacks don’t only nest on one beach but nest in a region, possibly nesting on more than one beach in a season. This is useful because several leatherback nesting beaches have shifting sands or are exposed to heavy erosion. Females lay about 7 clutches of 50-100 eggs each season at 9 to 10 day intervals. These eggs weigh about 80g each making them the largest of all sea turtle eggs. The nesting process takes 1.5 to 2 hours and each female will return to nest every 2 to 4 years.

The eggs take 2 months to develop and about 50% of eggs in undisturbed nests hatch successfully. This is much lower than the success rate of other sea turtles. The sex of the hatchlings, as with other sea turtles, is determined by temperature. Temperatures below 29.5⁰C yield mainly males and above yield mainly females.  The hatchlings are the largest of all sea turtles hatchlings despite weighing only 45g. They surface at night to avoid sea birds and once they have made their way to the sea they swim non-stop for 6 to 7 days. They are carried by currents in convergence zones where it is thought that they survive in floating vegetation. These hatchlings are the fastest growing of all reptiles and reach adulthood in 7 to 13 years. In order to maintain this rate of growth, leatherback hatchlings eat their weight in jellyfish every day.

Adults feed primarily on jellyfish but also eat crabs and other soft-bodied animals. The leather-like carapace of these turtles allows them to dive to depths of over 1200m to find food. A hard shell could crack under this sort of pressure but the flexible carapace is just compressed, leaving the turtle unharmed. They are also able to maintain a body temperature that is over 20^oC higher than the surrounding water so they are able to keep active in cold deep water.

Survival

It is no secret that leatherback numbers are declining. It was estimated that there were 115,000 nesting females in 1980. This figure declined to just 36,500 in 1996. There were 10,000 nests in Malaysia in 1956. In 2003 there were just 2. This decline is caused almost entirely by human activity. Adult females hunted on the nesting beaches of Mexico, Panama and other countries coupled with turtles being caught in drift nets decimated the adult population. 50 years of poaching almost all the eggs of many beaches meant that there weren’t enough hatchlings to replenish the dwindling adult population.

However whilst changing opinion means that actions are being taken to prevent poaching and deaths caused to turtles by nets, the greatest threat to leatherbacks is long line fishing. It is estimated that one leatherback is caught by each 1000 hooks set and 16% of hooked turtles die. This doesn’t seem like much but with 1.4 billion hooks set each year it adds up to a large amount of hooked turtles each year. It is estimated that of the 32,000 juvenile and adult turtles in the Pacific in 2000, 20,000 were caught on long lines. Another modern problem is the fact that turtle excluder devices save the lives of green, olive ridley and hawksbill turtles but are too small to save large leatherbacks.

Amongst all of these negatives there are some positives. 20 years of conservation efforts on St. Croix and a 4 year campaign in KwaZulu South Africa have seen leatherback number increase from 20 to 100 nesting females each year. Another example is Las Baulas Park, an area where all leatherback eggs were poached. Local land owners tried and failed to overturn a decree that made this area a national park.