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Recovery Strategy for the Leatherback Turtle

Habitat

2.9 Habitat Requirements 

To protect and recover leatherback turtles, it is essential to understand the full range of habitats required and how these habitats are utilized both spatially and temporally.  For the endangered leatherback turtle, the full range of habitat use is poorly understood (COSEWIC, 2001).  The details of leatherback migrations remain elusive, in part because the turtles occur far from land and travel such great distances (Lutz, 2003).  However, recent and ongoing studies will soon yield more specific information on the habitat requirements of the leatherback turtle in the northwest Atlantic.

Nesting

Little is known about the breeding habitats of leatherbacks, although Eckert and Eckert (1988) proposed that mating takes place outside of the nesting grounds, prior to female migrations to their nesting beaches.  Adult female leatherbacks nest every 2-3 years on high energy, open access, sandy beaches in the tropics that tend to be adjacent to deeper waters.  The largest leatherback nesting colony in the Western Atlantic is located in French Guiana and Suriname (Pritchard and Trebbau, 1984).  In the Atlantic and Caribbean, other significant leatherback nesting assemblages are found in the U.S. Virgin Islands (principally St. Croix), Puerto Rico, southeastern Florida, Guiana, Columbia, Panama and Costa Rica (NMFS and USFWS, 1992).  Little is known about the habitat requirements of post-hatchlings and juveniles.

Foraging

Leatherbacks normally inhabit areas where prey productivity is high, along oceanic frontal systems and along vertical gradients located at oceanic fronts (Lutcavage, 1996).  Doctoral thesis work by James (pers comm.) suggests that adult turtles aggregate at oceanic fronts and in specific areas with unique ocean circulation characteristics: shelf slope fronts, upwelling fronts, and western current boundary edges (James et al. 2005a).  This behaviour is likely related to the concentration of jelly-plankton in these areas.  Therefore, adult leatherback habitat may be determined by prey abundance, with turtles moving from offshore waters into coastal areas to exploit the seasonal production of jellyfish.

Eastern Canadian waters represent a common destination for sub-adult and adult leatherback turtles undertaking lengthy migrations from southern latitudes.  While the proportion of the Atlantic leatherback population utilizing Canadian waters is not known, each year large numbers of turtles from nesting areas in Florida and South and Central America (including French Guiana, Suriname, Costa Rica, Panama, Trinidad and the Antilles) aggregate here to feed.  As such, Atlantic Canada provides important foraging habitat for this species, and may offer seasonal densities of prey that are not widely available in other areas of the northwest Atlantic.

Sightings data, telemetry data and fisheries observer data suggest that most leatherbacks enter shelf and shelf slope waters from late May to September, although they may remain in Canadian waters for several months and depart as late as the middle of December.  Some turtles move from shelf waters to pelagic feeding areas in the fall before assuming a southward migration.  There is some evidence(Goff and Lien, 1988)to suggest that small numbers of turtles may be present in Canadian waters during the winter months; however, such behaviour does not conform to the typical migratory pattern for the species.

During the summer and fall foraging period, leatherbacks are broadly distributed in shelf waters off the northeastern United States, Nova Scotia, and southern Newfoundland.  While there appears to be significant inter-annual variation in both leatherback abundance and in the temporal and spatial characteristics of preferred foraging areas in Canadian waters, some areas do appear to be used by turtles every year.

Leatherbacks occur off the southwest coast of Nova Scotia throughout the foraging period and off the south and east coasts of Cape Breton in late summer and fall.  The species is rarely observed in the northern half of the Gulf of Maine and the Bay of Fundy.  Turtles regularly enter waters off the south coast of Newfoundland, and off the Magdalen Islands and north coast of Cape Breton Island (Gulf of St. Lawrence) during their foraging period.

While some turtles spend long periods of time foraging in specific areas (e.g., slope waters east of the Fundian Channel), other turtles may forage for several weeks in multiple, often disparate locations, including waters corresponding to both Canadian and American jurisdictions.  Data from turtles equipped with satellite tags in shelf waters seldom indicates subsequent extensive foraging in temperate waters far beyond the shelf break; however, as leatherbacks are incidentally captured in pelagic fisheries operating at high latitudes (Witzell, 1999; Lewison et al., 2004), it is reasonable to expect that some animals move onto the shelf after foraging in pelagic habitats, while others may migrate to and remain in these areas throughout the summer and fall foraging period (Eckert, 1998).

The diet of leatherbacks in northern waters of the Atlantic has been studied, and the species of jellyfish which they prey upon have been identified (Hartog & Nierop, 1984; Holland et al., 1990; Bleakney, 1965; James & Herman, 2001). However, relatively little is known about the biology of these jellyfish in this region.  Changes in the distribution and abundance of jellyfish may help explain annual variation in the number of turtles using Canadian waters and the timing and locations of turtle aggregations.

3.0 CRITICAL HABITAT [1]

Critical habitat as defined under section 2 of SARA is the “habitat necessary for the survival and recovery of a listed wildlife species and that is identified as the species’ critical habitat in the recovery strategy or in an action plan for the species”.

While the state of knowledge on habitat requirements of leatherback turtles in Canadian waters is increasing as new scientific evidence becomes available, it is currently not possible to identify critical habitat for this species.  As set out in SARA, if information is inadequate to identify critical habitat within the recovery strategy, a schedule of studies must be prepared.  Such a schedule, when implemented, will yield new information to enable the species’ critical habitat to be described.

Appendix II includes a list of research and monitoring activities that collectively, constitute a schedule of studies.  It is hoped that the results of this work will allow Fisheries and Oceans to be able to identify the critical habitat for Atlantic leatherback turtle in a recovery action plan, which will be developed once the activities outlined in the Appendix has been completed.



[1] SARA requires recovery strategies to include “an identification of the species’ critical habitat, to the extent possible, based on the best available information, including the information provided by COSEWIC” [SARA, s.41(c)].