There are seven sea turtle species recognized in the world today:
Green turtle – Chelonia mydas
Hawksbill turtle – Eretmochelys imbricata
Loggerhead turtle – Caretta caretta
Leatherback turtle – Dermochelys coriacea
Kemp’s ridley – Lepidochelys kempii
Olive ridley – Lepidochelys olivacea
Flatback turtle – Natator depressus
Five of the world’s seven sea turtle species are known to occur in Bermuda waters and are discussed below.
Nearly all sea turtles found in Bermuda waters are immature. Bermuda appears to be a place where young sea turtles grow up separate from adult animals. Nearly all that grow up here will return to the Caribbean Sea before they mature.
This large species, with adults averaging 136 kg (300 lbs) in weight, is sought after worldwide for its meat. This has resulted in an Endangered status designation for this species according to the IUCN. Their name comes from the greenish colour of the body fat which has been used for centuries to make turtle soup.
The olive-brown shell is often patterned with darker streaks. Posthatchlings eat both plant and animal matter, but older green turtles are unique among sea turtle species in being strict herbivores, feeding almost exclusively on sea grasses and algae.
The green turtle is the most common sea turtle species on the Bermuda Platform. Immature animals can be seen feeding on any of the sea grass pastures on the Bermuda Platform.
The hawksbill turtle has a bird-like beak from which it gets its name. It uses this beak to feed on sponges that form the majority of its diet even though sponges can be loaded with glass-like spicules. Immature hawksbills are a regular inhabitant of the coral reefs surrounding Bermuda. As adults they can grow to nearly 90 kgs (200 lbs), but those found in Bermuda waters are immature and average about 10 kgs (22 lbs).
The shell scutes of this species are a highly prized commodity like elephant ivory or rhinoceros horn and this species has been exploited worldwide for most of recorded human history. This has led to a Critically Endangered designation for this species. Furthermore, because hawksbills are important predators of sponges, they could potentially reduce competition by sponges on coral reefs. Thus, reef health may depend in part on healthy populations of hawksbill turtles.
This species has a large, broad head and powerful jaws, which it uses to dine on shellfish. Loggerheads eat crabs, clams, mussels, sea urchins, jellyfish and are even capable of crushing very thick-shelled conchs. This species has a reddish-brown shell and grows to 159 kgs (350 lbs) or more. It is considered to be Endangered by the IUCN.
Hatchling loggerheads spend their first months well camouflaged in floating rafts of Sargassum weed. During the winter months, juvenile loggerheads are found stranded on Bermuda shores after heavy storms. They are typically found tangled in small clumps of Sargassum weed.
In 1990 and again in 2005, a single nest constructed by a loggerhead turtle was discovered on a beach at the eastern end of Bermuda. These are the first records of sea turtle nests in Bermuda since the early 1930s. The loggerhead is threatened by incidental capture in the nets of commercial trawl fisheries, and by long lines which target several fish species.
The leatherback is a species with a bizarre shell adapted to its pelagic, deep-diving lifestyle. This is the largest living reptile, growing to 909 kgs (2,000 lbs). Since most of its life is spent in the open ocean, the leatherback’s life remains largely a mystery.
It gets its name from the thick, leathery skin that covers the bone of the shell; it lacks the typical hard scales of most turtles. The bony part of its shell is made up of thousands of small interlocking bones, like the pieces of a puzzle. Unlike the other sea turtle species, the leatherback roams the seas as far north as Alaska, Nova Scotia and even Iceland, and it is capable of deep dives in excess of 1,000 meters (3,280 feet).
A perfect diving machine, this species is able to maintain its body temperature as much as 10 degrees above that of surrounding waters; this is presumably an adaptation for survival in cold seas.
Leatherbacks feed almost exclusively on jellyfish, and this can lead to accidental ingestion of plastic bags. Considering jellyfish are ninety-seven percent water, one has to wonder how such an enormous, ocean-going reptile subsists on such a diet. No doubt the quantity of jellyfish consumed is vast. Leatherbacks are only occasionally seen offshore around Bermuda, presumably as they pass by our oceanic island on their long-distance journeys.
This rare species is an occasional waif in Bermuda waters. It is a Critically Endangered species that goes through much of its life cycle within the Gulf of Mexico and along the eastern seaboard of the United States. However, some immatures venture out into the Atlantic, and at least four have found their way into Bermuda waters.