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Recovery Strategy for the Leatherback Turtle

2.5 Distribution

2.5.1 Global Range

Leatherback turtles are capable of tolerating a wide range of water temperatures and have the most extensive geographic range of any reptile species.  Leatherbacks undertake extensive migrations throughout the tropical and temperate waters of the Atlantic, Pacific and Indian oceans, with a northernmost recorded latitude of 70° 15’N (Gulliksen, 1990) and a southernmost of approximately 27°S (Boulon et al., 1988).

The largest Atlantic nesting colonies are located in French Guiana and Suriname in South America, and Gabon in Africa.  Nesting also occurs in lower densities throughout the Caribbean and in Brazil.  Florida is the only state in the continental U.S. known to support a significant number of nests (Calleson et al, 1998).  Rabon et al. (2003) recently summarized leatherback nesting activity north of Florida and reported seven confirmed nests from the state of North Carolina.  This is the northern extent of the nesting range in the northwest Atlantic.  It is believed that all major nesting sites for this species are known and nesting activity has been intensively monitored at most of these sites for several years (Spotila et al., 1996).

At the end of the nesting season, an unknown portion of the population of leatherbacks migrates northward to temperate waters.  In the course of these migrations, individual turtles may attain speeds of over 9km/h (Keinath & Musick, 1993).  Studies of leatherbacks in the Gulf of Mexico (e.g., Fritts et al., 1983), off the Atlantic coast of the United States (e.g., Lazell 1980; Shoop & Kenney, 1992) and off the east coast of Canada (James, 2000; Lawson and Gosselin 2003) suggest that these turtles may preferentially inhabit continental shelf waters.  Offshore, leatherbacks are regularly present along thermal fronts, including the edges of oceanic gyre systems (e.g., Collard, 1990; Lutcavage, 1996).  These are highly productive areas, concentrating jellyfish and other soft-bodied invertebrates on which leatherbacks feed.

New data regarding leatherback turtle distribution continues to be gathered through a number of tagging methods (i.e., flipper tagging, internal Passive Integrated Transponder (PIT) tags and satellite tagging).  Through flipper tagging, leatherbacks from the western Atlantic population (Guiana) have been recorded off west Africa, in the Gulf of Venezuela, in the Gulf of Mexico and on the Atlantic coast of the United States (Pritchard, 1976).  Since 1978, others have been captured along the eastern United States, between Florida and South Carolina (Girondot & Fretey, 1996).  Leatherbacks tagged in French Guiana have also been captured in the northeast Atlantic off the coasts of France, Spain and Morocco, less than 12 months after nesting (Girondot & Fretey, 1996).  In 1987, a leatherback tagged 128 days previously in French Guiana was discovered entangled in fishing nets in Placentia Bay, Newfoundland (Goff et al., 1994).  The turtle had travelled a minimum straight-line distance of over 5000km.  The northernmost records for Atlantic Canada are of leatherbacks entangled in gear (2, 1986 and 2004) or free-swimming (1, 1986 at almost 54 N) along the coast of Labrador (DFO, 2005b).

Through satellite tracking (e.g., Eckert et al, 1989; Morreale et al., 1996; Hughes et al., 1998), more direct studies of leatherback distribution and migration have been undertaken.  One study revealed long-distance movements from tropical nesting beaches to temperate waters of the north Atlantic (Eckert, 1998).  Two leatherbacks tagged on a nesting beach in Trinidad migrated north to waters between 40 and 50 degrees latitude before swimming south to the coast of Mauritania, Africa (Eckert, 1998).  More recently, 39 leatherbacks satellite-tagged in eastern Canadian waters were tracked on their migrations to subtropical and tropical waters (James, unpublished data).  Ten of these turtles represent the first male leatherbacks to be tracked via satellite telemetry.

Relevant information has also been obtained through studies of the barnacles that leatherbacks host.  For example, Zullo & Bleakney (1966) reported barnacles, typical of tropical and subtropical waters (Stomatolepas elegans), on the skin of leatherbacks recovered off Nova Scotia.

In Canada, leatherbacks from the Pacific population are found seasonally off the coast of British Columbia, foraging between July and September (Stinson, 1984).  Although more sightings occur every year, there are a limited number of areas where leatherbacks are routinely observed, and sightings are generally made by fishers.  Recently, reports by recreational boaters have become more frequent.  These observations have been recorded through the Queen Charlotte Islands and increasingly throughout the protected waters of the Georgia and Hecate Straits (Pacific Leatherback Turtle Recovery Strategy, 2005).

2.5.2 Range in Atlantic Canada

 Although leatherbacks do not nest in Canada, adult turtles occur annually in Atlantic Canadian waters to forage, with the majority of turtles present between June and November (Figure 2). Figure 2 includes a compilation of published and previously unpublished distributional records for the leatherback turtle in Atlantic Canada.  This data is based on individual stranding and entanglement records of both live and dead turtles, as well as at-sea sightings.

With the observed variability in numbers of individuals that migrate annually through Canadian waters and the difficulty in censusing the population at sea, documentation of leatherbacks in Atlantic Canada has been limited.  This has resulted in conservative historical evaluations of leatherback abundance (e.g., Cook, 1981; Gilhen, 1984).  Yet, a relatively large seasonal population has recently been identified through efforts described below.

Bleakney (1965) was the first to document scientifically the occurrence of leatherbacks in eastern Canada and his analysis of 26 records of leatherbacks in this region (1889-1964) suggested a seasonal, rather than accidental, movement of the species into the cold waters of the northwest Atlantic.  Recent research by James (2000; James et al. 2005a, 2005b) and DFO scientists (unpublished) supports the conclusion that leatherbacks regularly enter temperate waters off eastern Canada.  Peak leatherback occurrences in Canadian waters occur during August-September but there are records for leatherbacks in Canadian waters for most months of the year (McAlpine et al., 2004).

Specifically, leatherbacks have been recorded off the coasts of Nova Scotia (e.g., Bleakney, 1965; James, 2000), Newfoundland (e.g., Goff & Lien, 1988; Lawson and Gosselin, 2003), and Labrador (Threlfall, 1978; DFO, 2005b).  Reports from New Brunswick come from turtles sighted in the Bay of Fundy, the Northumberland Strait and the Gulf of St. Lawrence.  In Prince Edward Island, a small number of records come from coastal strandings and reports made by fishers.  Leatherbacks have also been reported in the Gulf of the St. Lawrence off Quebec (e.g., D’Amours, 1983; Bosse, 1994).  Cultural artefacts from Baffin Island suggest that leatherbacks are occasionally encountered in that region of the north Atlantic (Shoop, 1980).

There has been some question as to whether juvenile leatherbacks occur in Canadian waters. Based on a review of all sightings of leatherback sea turtles of  <145cm curved carapace length (ccl), Eckert (1999) found that leatherback juveniles remain in waters warmer than 26°C until they exceed 100 cm.  These results lead us to believe that it is unlikely that juveniles venture into Atlantic Canadian waters.

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Figure 2.  Occurrence of the leatherback turtle, Dermochelys coriacea, off eastern Canada.  Shaded areas show the location of concentrations of observations and are taken from Goff and Lien (1988; A), Witzell (1999 and DFO, 2005; B), and James (2000; C).