The Loggerhead Turtle

About Guy:
Guy Harvey

On a fine sunny, calm morning recently, we ran up to East End to do a dive at the Dragon’s Lair, a popular spot with caves and swim-throughs often populated by tarpon. Earlier that week, my daughter Jessica and I had dived there and found a big school of silversides.

We had rented a camera from Cathy Church and returned to the site. Jessica and I swam up to the entrance of the cave and could see the silversides and several tarpon, but before going inside I took a quick look around. There were several big dog snappers hanging about, a big cubera, many bar jacks and a black grouper lounging under a wide coral ledge not far away. I motioned to Jessica to get a shot of the black grouper when around the edge of the coral buttress swims… a huge loggerhead turtle.

I could not believe our luck. Ten seconds later and we would have gone inside the caves. Distinguished from the green or hawksbill turtle by its big head and large crushing jaws, the loggerhead swam slowly towards Jessica as she quickly got into position for the shot, and then kept backing away from it as it almost swam into her. Its shell had a red brown colour and fins, plastron and face were yellow/ochre. I was still mesmerized as she and the turtle danced along above the coral, heading away from the caves. It was a large male turtle about 200 pounds and was totally relaxed with her swimming beside it. It eventually paddled upward for a breath and headed on its way into deeper water.

What a great experience. It was only the second loggerhead I have seen in 10 years in Grand Cayman and once before I encountered one off the Port Royal Cays in Kingston. That one had the left rear quarter of its body and shell, including the left rear flipper, chopped out (must have been a tiger shark bite) but it was all healed over. It is quite remarkable that an animal can recover so well from such a large injury! Loggerheads are rare in tropical waters, but fairly common further north in sub tropical and temperate waters. They may be uncommon here in the Cayman Islands but are the most widely distributed of all sea turtle species, occurring in all oceans and in the Mediterranean Sea.

There is a concentration of loggerheads in the southeast of the US continent, and the Atlantic coast of Florida is particularly favoured for nesting where some 70,000 nest per year in the greatest concentration of nesting loggerheads. At intervals of 12 to 17 days during the nesting season loggerheads lay an average of four clutches of about 110 eggs. They return to nest every two to four years. Loggerheads may not become mature for 17 to 30 years and may live as long as 70 years and weigh up to a thousand pounds. They are a slow growing, long lived animal.

Once the young turtles hatch they run the gauntlet of formidable predators just like all other turtle species in going from the nest to reach the sea at night. Once there the juvenile loggerheads swim offshore and seek shelter near floating objects, particularly in Sargassum weed. These juveniles ride the Gulf Stream and other ocean currents, feeding opportunistically on anything plant or animal such as barnacles, crab and fish larvae, fish eggs, algal and hydrozoan colonies attached to flotsam which they find coexisting in the mats of weed.

The juveniles are preyed upon by sharks, particularly tiger sharks during this growth phase and may spend six to 12 years in the open ocean after which they return to the continental shelf and take up a more benthic existence feeding on the sea floor in water as deep as 600 feet. Here they feed on a variety of crabs, lobsters, shrimp, mussels, juvenile conch, whelks, tubeworms, sea anemones and will even dig in soft substrate for buried gastropod and bivalve molluscs.

The loggerhead is a keystone species in the world’s oceans. As a carnivore it plays a central role in the food chain and is dependent upon invertebrate populations that form the vast majority of its food supply. By digging around on the bottom loggerheads change ocean bottom communities both in physical structure and in terms of community organization of the areas in which the turtles forage. They also support a large array of plants and animals that attach to their shells and ride through the ocean with the turtles.

It takes about 25 years for a loggerhead hatchling to become a reproducing adult. During this time it must survive the natural and human dangers firstly in the open ocean and then in coastal waters where there is more concentrated fishing activity, garbage, pollution, boating activity and particularly bottom trawling for shrimp. The advent of turtle exclusion devices in the bottom trawl nets greatly increased the odds of survival for this species. Making its way through all these obstacles a sub adult turtle must then compete with humans for its food supply of conch, clams, crabs and lobster. In moving offshore to the continental margin it encounters more long-lines, gill nets and more trawlers.

To maintain a viable population, loggerheads, like other long-lived vertebrates, must sustain high annual rates of survival. Loggerheads are classified as endangered by the IUCN and are listed as Appendix 1 by CITES making international trade in this species illegal. Many countries now work together to protect this and other turtle species including protection of nesting beaches and the widespread use of turtle exclusion devices in commercial trawling operations around the world.   WH

It is our collective responsibility to conserve marine species and maintain the biodiversity of the planet.

Fish responsibly, dive safely.
Guy Harvey PhD.
www.guyharveyoceanfoundation.org.

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