07. Chickadee Notes

Leatherback Turtle in New Brunswick

Status

Leatherback Turtle

The Leatherback Sea Turtle, Dermochelys coriacea, has been reported from New Brunswick on fewer than a dozen occasions, although the species is considered of regular occurrence in Atlantic waters from June to October. Most recently in New Brunswick two turtles were seen in September 1992. Most reports are the result of entanglements with fishing gear along the Northumberland Strait/Gulf of St. Lawrence, but this turtle has also been observed in the lower Bay of Fundy. The species nests on beaches in tropical and subtropical parts of the world but routinely moves into northern latitudes late in the summer. The Leatherback is considered endangered worldwide and is listed as such by the federal-provincial Committee on the Status of Endangered Wildlife in Canada. Trade in Leatherback turtles, their parts, or products manufactured from them, is prohibited by the Convention on International Trade in Endangered Species, of which Canada is a signatory. The most recent estimate sets the global population of this species at 115,000 mature females. Outside Canada the species is widely protected, including in the United States, Mexico, South Africa, Sri Lanka and Australia and in some countries in Central and South America.

Natural History

The Leatherback is the largest living species of turtle in the world. Adults may approach 1.8 m in carapace length and weigh more than 575 kg. A Leatherback of average proportions that became entangled in fishing gear near Shediac, New Brunswick in September 1992 weighed 318 kg.

the leatherback is noted for regular late summer and early autumn appearances in cold northern seas...

In appearance the Leatherback is the most distinctive of the sea turtles. Unlike other turtles, in which a bony carapace is covered with horny scutes, the Leatherback has a smooth, rubbery skin covering a shell composed of a thick, oily, cartilage. The shell is barrel shaped with a series of longitudinal ridges tapering to a blunt tip over the tail. The front flippers of the Leatherback are long and are well suited for propelling the animal forward through the water. The hind limbs, though smaller, are also streamlined and like the front flippers, are clawless. Leatherback Turtles are black on their upper surfaces and whitish underneath, with a soft, velvety skin that is devoid of scales. The skin of the dorsal surface may be heavily spotted with white and is often tinged with pink.

The Leatherback breeds on tropical and subtropical beaches throughout the world. The species is basically pelagic ranging across the Atlantic, Pacific, and Indian oceans and into the Mediterranean. There have been few recaptures of tagged adults but some returns have shown movements of more than 5,000 km, the longest migrations of any reptile. Although sea turtles are generally animals of warmer waters, the Leatherback is noted for regular late summer and early autumn appearances in cold northern seas off western and eastern Canada, Alaska, the British Isles and Norway. These movements into northern waters probably represent feeding forays as the turtles follow concentrations of jellyfish, the mainstay in their diet.

Breeding age is unknown and there is little information available on growth between hatching and adult size.

Reptiles are extremely rare in cold northern waters, and in this respect the Leatherback is exceptional. There is now good evidence that adult Leatherbacks are able to generate heat internally and maintain a core body temperature well above that of summer seawater in this region. The sheer mass of the animal, combined with anatomical adaptions such as countercurrent heat exchangers in the flippers and a thick insulating layer of fat make this possible. Leatherback Turtles are superb divers and are probably able to remain submerged for several hours at a time.

Breeding age is unknown and there is little information available on growth between hatching and adult size. In the Atlantic nesting occurs from April through November, but the Pacific race apparently nests throughout the year. Females may nest four to ten times a year, normally at night, with an interval averaging 10 days. Each clutch consists of 50 to 170 eggs, but a significant number of these are yolkless. Despite the large size of the Leatherback, this species lays fewer eggs than nearly all other sea turtles. Following an incubation period of 53 to 74 days, hatchlings of 60 to 63 mm carapace length emerge. Since the top eggs in the egg chamber are covered with about 100 cm of sand the hatchlings face a formidable challenge in burrowing to the surface. The task becomes a communal effort, with numerous hatchlings scraping upward at about the same time. In this way the ceiling of the nest is scraped down while the floor is correspondingly raised. Finally the thinning roof collapses, allowing all the turtles to emerge together. Although they immediately scramble down the beach toward the sea, a great many of these hatchlings will fall victim to such predators as crabs, monitor lizards, mongoose, gulls, crows, and vultures en route. For those that do reach the water, predatory fish, squid, and octopi lie in wait. Even with all these obstacles, and others to adulthood, it is still staggering to consider that each female Leatherback must lay thousands of eggs over a lifetime to produce a single breeding adult pair.

Helping Out

Leatherbacks spend most of their lives at sea, where adults probably have few enemies save the occasional shark, Killer Whale, or large ship propeller. The principal threats to the future of the Leatherback occur on the animals nesting beaches in the tropics. Although the meat of the Leatherback is not prized and nesting females are seldom killed, egg collecting is a serious problem in some areas. The commercial development of nesting beaches is also a threat to Leatherbacks. Once they have started to dig the nest leatherbacks seem imperturbable, but if disturbed during their crawl up the beach they will often return to the sea. The degree to which marine turtles are affected by pollution at sea is unknown. It is known that Leatherback turtles commonly mistake floating plastic bags for jellyfish. There are several cases documented where obstruction of the intestine of the turtle appears to have been the result of ingesting such garbage. We can all help keep our beaches and coastal waters free of rubbish, thereby reducing one hazard Leatherbacks in New Brunswick waters may face. On the rare occasions Leatherbacks are encountered off our coast it is often because they have become entangled in fishing gear. Such turtles should be removed immediately and released unharmed. The observation, accompanied by a photograph where possible, should be reported to the New Brunswick Museum where records of such occurrences are saved.

Further Reading

Cook, F.R. 1981. Status report on the Leatherback Turtle, Dermochelys coriacea. Committee on the Status of Endangered Wildlife in Canada, Ottawa. 17 pp.

Ernst, C.H. and Barbour, R.W. 1972. Turtles of the United States. The University Press of Kentucky, Lexington, Kentucky, 347 pp.

Lazell, J.D., 1980 New England waters: critical habitat for marine turtles. Copeia (1980):290-295.

Pritchard, P.C.H. 1971. The Leatherback or Leathery Turtle, Dermochelys coriacea. IUCN Monograph No 1., International Union for Conservation of Nature and Natural Resources, Morges, Switzerland, 39 pp.

Pritchard, P.C.H., 1982. Nesting of the Leatherback Turtle, Dermochelys coriacea in pacific Mexico, with a new estimate of the world population status. Copeia (1982):741-747.