Leatherback turtle (Dermochelys coriacea) COSEWIC assessment and status report: chapter 2
Executive Summary
Dermochelys coriacea
Species information
The leatherback turtle (Dermochelys coriacea) is a large marine turtle; specimens can grow up to 2 m long and have an average weight of 500 kg. The leatherback’s carapace is not covered by scales, but instead has a leathery, cartilagenous covering. The paddle shaped front flippers are usually equal to or longer than half the animal’s body. Leatherbacks have black or dark blue backs with white and pink blotches and a white belly. Individual turtles can be recognized by the size, shape, colour and pattern of the “pink spot” on top of their heads. The leatherback turtle is unique in being the only marine turtle that does not have scales.
Distribution
Leatherbacks range from 70° 15’N to 27°S in the Atlantic, Pacific and Indian Oceans. The major nesting beaches are located in Mexico, Costa Rica Irian Jaya, French Guiana, Suriname and Gabon. In Canada, there have been sightings of the turtles in the waters off Nova Scotia, New Brunswick, Newfoundland, and Prince Edward Island.
Habitat
Virtually nothing is known about hatchling and juvenile habitat requirements, however, since they are never seen in temperate waters, it can be assumed that the leatherbacks gain cold tolerance as they mature, possibly due to increased body size. The adult leatherbacks are highly migratory and spend the majority of their lives in the open sea. They are regularly observed along the continental shelf off the coast of Canada, presumably because of a high concentration of prey. Their use of temperate water habitat seems to be dependent on prey abundance.
Biology
Not much is known about leatherback mating, either in terms of where or when it occurs. The females nest in the tropics on open beaches with minimal amounts of abrasive material. They prefer beaches with deep-water approaches because they are very awkward on land. The leatherback females excavate the nest with their hind flippers and lay 50-166 eggs; a large number of yolkless eggs are often laid at the top of the nest. They lay an average of 6 clutches each season, at 8-12 day intervals. The eggs hatch in about 60-65 days. The sex ratio of the hatchlings is determined by nest temperature during development (temperature dependent sex determination). There is high mortality in the egg and hatchling stages as a result of poor nest site selection and predation. The adult leatherbacks have few natural predators -- only sharks and killer whales.
Leatherbacks can retain an internal body temperature 18° higher than the ambient temperature, allowing them to survive in colder environments. They also have specialized tear glands to expel the excess salt that they obtain from their diet of jellyfish. The main prey items are jellyfish and other soft-bodied vertebrates, but added invertebrates are often eaten incidentally along with the preferred prey. Leatherback turtles migrate to tropical waters to nest and then follow the abundance of jellyfish into temperate waters. The turtles are attracted to the continental shelf area, and areas of thermal, salinity or colour changes because of the high levels of prey.
Population sizes and trends
Population estimates of leatherback turtles are based on the number of nesting females. Estimates made in 1982 (115,000) and 1995 (approximately 34,500) suggest large population declines in the Pacific. The Atlantic population appears to be more stable, but shows dramatic fluctuations in the number of nesting females from year to year. There are no good population estimates for leatherbacks in Canadian waters.
Limiting factors and threats
Nests are subject to both natural and human created pressures. The turtle’s preference for open beaches as nest sites results in nests being destroyed by flooding and erosion. Increased human use of the beaches discourages nesting, while after nesting humans harvest the eggs for consumption. Since the sex ratio of the nests is determined by temperature, there are suggestions that global warming could affect the demographics of the leatherback populations.
The adult turtles are threatened by entanglement in fishing gear, which can result in death by drowning or serious injuries. In addition, adult leatherbacks often mistake floating garbage as jellyfish (for example, plastic bags). Ingestion of such materials inevitably results in death.
Special significance of the species
The leatherback is one of only two marine turtles that are regularly found in Canadian waters.
Existing protection
The leatherback turtle is listed as globally endangered and endangered in Canada. It is listed as critically endangered by CITES, however, it is categorized as Appendix I or II, depending on country. Since it is a migratory species, these inconsistencies in level of protection pose serious problems for conservation. Some of the species’ critical nesting beaches have been protected as national parks or reserves. Also, devices to prevent turtles from drowning in fishing gear have been mandated for use in several countries.
COSEWIC MANDATE
The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) determines the national status of wild species, subspecies, varieties, and nationally significant populations that are considered to be at risk in Canada. Designations are made on all native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fish, lepidopterans, molluscs, vascular plants, lichens, and mosses.
COSEWIC MEMBERSHIP
COSEWIC comprises representatives from each provincial and territorial government wildlife agency, four federal agencies (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biosystematic Partnership), three nonjurisdictional members and the co-chairs of the species specialist groups. The committee meets to consider status reports on candidate species.
DEFINITIONS
The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list.
Environment Environnement Canada Canada Canadian Wildlife Service canadien |
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The Canadian Wildlife Service, Environment Canada, provides full administrative and financial support to the COSEWIC Secretariat. |
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