Leatherback turtle in Atlantic Canada (Dermochelys coriacea) recovery strategy: chapter 3

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2. Background

• 2.1 Current Canadian Status
• 2.2 Global Status History
• 2.3 Legal Protection
• 2.4 General Biology and Description
• 2.5 Distribution
• 2.6 Population Size and Trends
• 2.7 Biological Limiting Factors
• 2.8 Threats
• 2.9 Habitat Requirements

2.1 Current Canadian Status

Common name: Leatherback turtle

Scientific name: Dermochelys coriacea

Status: Endangered

Reason for designation: The leatherback turtle is undergoing a severe global decline (> 70 % in 15 years). In Canadian waters, incidental capture in fishing gear is a major cause of mortality. A long lifespan, very high rates of egg and hatchling mortality, and a late age of maturity makes this species unusually vulnerable to even small increases in rates of mortality of adults and older juveniles (COSEWIC, 2003)

Occurrence: Pacific Ocean and Atlantic Ocean

Status history: Designated Endangered in April 1981. Status re-examined and confirmed in May 2001.

This statement of designation is from the report produced by COSEWIC following assessment of leatherback turtles in both Atlantic and Pacific Canadian waters. It bears noting that incidental catch of individuals in fishing gear is the most well documented source of anthropogenic mortality to leatherback turtles in Canada, however other sources of mortality both within and outside Canadian territorial waters have contributed to overall population declines. Threats to leatherback turtles are further elaborated on under section 2.7.

2.2 Global Status History

The leatherback turtle is currently both nationally endangered (Cook, 1981; COSEWIC 2001) and globally critically endangered by the World Conservation Union (IUCN). It has been listed as endangered throughout its range since 1970 under the U.S. Endangered Species Act (ESA).

2.3 Legal Protection

2.3.1 Canada

Leatherback turtles are listed under Schedule 1, Part 2 of SARA and therefore, its provisions against the killing, harming, harassing, capturing or taking of individuals apply.

In addition to SARA , other federal statutes that offer legal protection for leatherbacks and their habitat in Canada include the Habitat Protection provisions of the Fisheries Act (1985) and the Oceans Act (1996), which gives DFO authority to create Marine Protected Areas to protect endangered and threatened species. The leatherback is also protected under the 1996 New Brunswick Endangered Species Act. However, as a migratory marine species, the leatherback turtle is ultimately under federal jurisdictional responsibility.

2.3.2 Globally

Globally, the leatherback turtle receives protection under the Convention for International Trade in Endangered Species of Wild Flora and Fauna (CITES). For countries that are signatories to the Convention, including Canada, CITES is an international agreement whose goal is to ensure that international trade in products derived from wild animals and plants does not threaten their survival in the wild. Leatherback turtles were listed in Appendix I under CITES in 1990, which permits trade only under exceptional circumstances.

Leatherbacks utilize nesting beaches and waters that are shared by many nations. The Inter-American Convention for the Protection and Conservation of Sea Turtles (IACPST) is the only international treaty dedicated exclusively to sea turtles, setting international standards for the conservation of protected sea turtles and their habitats. Canada is not a signatory party to this convention. Further, the Convention on the Conservation of Migratory Species of Wild Animals (CMS) has some provisions that address the harvest of endangered species.

International cooperation will be the key to effective protection of this animal. The Commission for Environmental Cooperation (CEC) has recently selected the Leatherback turtle as a pilot species for the development of a North American Conservation Action Plan. The CEC is an international organization created by Canada, Mexico and the United States to address regional environmental concerns, help prevent potential trade and environmental conflicts, and to promote the effective enforcement of environmental law. It is hoped that the Canadian Recovery Strategy will contribute to this Conservation Action Plan.

2.4 General Biology and Description

2.4.1 Phylogeny

One of only seven species of marine turtle, the leatherback (Dermochelys coriacea) is the sole member of the family Dermochelyidae, which diverged from other turtles 100-150 million years ago (Zangerl, 1980). Two subspecies have been described: Dermochelys coriacea coriacea (Linnaeus, 1766), the Atlantic leatherback, and Dermochelys coriacea schlegelii (Garman, 1884), the Pacific leatherback. However, these supposed sub-species are poorly differentiated, and distinctions based on colouration and differences in forelimb and head length are questionable (Pritchard, 1979). Therefore, one species is now generally recognized. Genetic analyses, revealing little divergence between Pacific and Atlantic populations (Dutton et al, 1996), have corroborated this view.

Low genetic variation between leatherbacks occupying Pacific and Atlantic waters may be a product of recent evolutionary separation between these populations. Alternatively, the leatherback's extraordinary migratory ability (e.g., Hughes et al, 1998) and two to three year intervals between nesting events (e.g., Hughes, 1996) may enable gene flow between these ocean basins (Binckley et al, 1998).

In Canadian waters, leatherbacks are derived from multiple nesting assemblages and may be considered a single population for management purposes. Canadian recovery efforts focus on two groups based on ocean basin: (1) the Pacific leatherback turtle and (2) the Atlantic leatherback turtle.

2.4.2 Appearance

Leatherback turtles lack a bony shell, and are the only soft-shelled species among all seven marine turtles. They may attain a carapace (or shell) length of nearly two metres. The tapered carapace has a four-centimetre-thick covering of tough, oil-saturated connective tissue covering a mosaic of thousands of small dermal bones (Pritchard, 1971). The body mass of the leatherback typically does not exceed 500kg (Zug & Parham, 1996) and the immense paddle-shaped front flippers often equal or exceed half the carapace length.

Leatherbacks lack the hard mandible structure of hard shelled turtles. Instead, the upper jaw has two tooth-shaped projections, flanked by deep cusps for cutting soft tissue. Their oesophagus is also lined with backward pointing spines to aid them in swallowing their jellyfish prey. The carapace of the turtle is black, or bluish-black, with scattered white and pink blotches, while the plastron is predominantly white. Each adult leatherback has a uniquely patterned "pink spot" on the top of the head (McDonald & Dutton, 1996).

The only visual way to distinguish male from female adult leatherbacks is by examining the tail length. The male's tail typically extends beyond the length of the rear flippers, while the female's tail is shorter than the flippers (Pritchard 1971).

Figure 1. Schematic depicting a mature adult leatherback turtle and key morphological features.

2.4.3 Foraging Ecology

Leatherbacks feed primarily on jellyfish (medusae) and other soft-bodied pelagic invertebrates (e.g., Lazell, 1980; Lutcavage & Lutz, 1986, Grant et al., 1996). Necropsies have identified many small fish, crabs, amphipods and other crustaceans in the digestive tracts of leatherbacks (Hartop & Van Nierop, 1984; Frazier et al., 1985). These may be jellyfish prey or commensal to jellyfish and are likely ingested incidentally by leatherbacks (Frazier et al., 1985).

The leatherback exhibits several adaptations for its diet of soft-bodied prey including a sharp-edged beak and backward-pointing spines in the throat, which likely assist in swallowing slippery prey (Bleakney, 1965). Since these soft-bodied prey are energy poor, consisting of about 95% sea water, small leatherbacks may have to consume an amount equal to their weight daily in order to maintain a normal metabolic rate (Lutcavage & Lutz, 1986). Therefore, leatherbacks must locate dense patches of food, which might explain why these turtles are numerous in coastal areas and along oceanic frontal systems where prey productivity is high (Shoop & Kenney, 1992).

Leatherbacks also exhibit deep diving behaviour at night in tropical waters, which reflects their foraging on medusae (Eckert et al, 1989). In eastern Canada, the distribution and movements of leatherback are thought to be closely associated with seasonally abundant prey, particularly Cyanea sp., their principal jellyfish prey (Bleakney, 1965; Goff & Lien, 1988; Shoop & Kenney, 1992; James, & Herman 2001).

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.

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).

2.6 Population Size and Trends

2.6.1 Global Population

As above, the leatherback turtle is difficult to census in the marine portion of its life cycle, as it is largely pelagic. Therefore, current population estimates are based on surveys of adult females encountered on monitored nesting beaches. Pritchard (1982) estimated that the overall world population was approximately 115,000 nesting females in 1980. In 1995, a study incorporating information from 28 nesting beaches throughout the world yielded a revised estimate of approximately 34,500 females; the lower limit was 26,200 and the upper limit was 42,900 (Spotila et al., 1996).

These figures reflect dramatic declines at several nesting locales, particularly in the Pacific (Chan & Liew, 1996; Steyermark et al., 1996; Eckert & Sarti, 1997) where recent trends suggest that this population is facing imminent extinction (Spotila et al., 2000). For example, there were 3103 leatherbacks nesting at Terengganu, Malaysia in 1968, 200 turtles in 1980, and only 2 in 1994 (Chan & Liew, 1996). Similar declines are occurring in Playa Grande, Costa Rica, where annual mortality of nesting females is over 30% (Spotila et al., 2000).

Although some nesting populations (e.g. St. Thomas, etc.) have been extirpated, the status of existing nesting population in the eastern Atlantic and in the Caribbean appears to be stable. Data collected in southeast Florida indicate an increasing in nesting, although it is important to note that there was an increase in survey effort (rather than area).

The largest leatherback rookery in the western Atlantic remains along the northern coast of South America in French Guiana and Suriname, and the nesting population in the trans-boundary region has been declining since 1992 (Chevalier & Girondot, 1998). Recent information suggests that western Atlantic populations declined from 18,800 nesting females in 1996 (Spotila et al., 1996) to 15,000 nesting females by 2000 (Spotila, pers. comm.).

While leatherback turtles may have shifted their nesting from French Guiana to Suriname due to beach erosion, it appears that the overall area trend of nests has been negative since 1987 (NMFS SEFSC 2001). Without information to determine whether turtles are nesting elsewhere, it can be assumed that that the western Atlantic portion of the population is being subjected to mortality beyond sustainable levels.

A number of studies have used aerial and shipboard surveys to estimate the seasonal occurrence of leatherbacks in waters off the continental United States (e.g., Hoffman & Fritts, 1982; Shoop & Kenny, 1992; Epperly et al., 1995). Shoop and Kenney (1992) found (after three survey years) that an average of 6.85 turtles are located in every 1000 km from near Nova Scotia to Cape Hatteras, North Carolina. The mean sighting latitude for leatherbacks was 40°05'N and the mean sea temperature was 20.4 °C. Total study area population during the summer was estimated to be 100-900 leatherbacks; this is a minimum surface estimate. Similar abundance estimates are not yet available for Canadian waters, as the limited linear aerial or transect-based shipboard surveys undertaken have been focused on cetaceans. Data have been gathered opportunistically from volunteer commercial fishers, who record sightings of leatherbacks while fishing or travelling to and from fishing grounds. Sightings and entanglement data have also been collected through phone and mail surveys, and through the entanglement and stranding networks.

2.6.2 Population in Atlantic Canada

Existing data on leatherback distribution reveal relatively large numbers of sightings in several popular fishing areas along the Scotian Shelf (James, 2000; James et al., 2005a & 2005b) and along the southeast coast of Newfoundland (DFO, 2005), however these sightings are biased toward areas where fishing activity occurs. Therefore, sightings and incidental captures of leatherbacks are most likely to occur in the heavily fished areas off the Scotian Shelf and the Newfoundland south coast. General baseline data about the abundance and distribution of the species throughout the region are lacking. With these limitations, it is not possible to precisely assess abundance in eastern Canadian waters.

In 1998 and 1999, 300 leatherback turtle sightings were documented by a fisher-scientist collaborative venture entitled the Nova Scotia Leatherback Turtle Working Group (NSLTWG). The NSLTWG group was initiated in Atlantic Canada to investigate the distribution of leatherback turtles in the northwest Atlantic (James, 2000). These numbers suggest that summer leatherback densities in eastern Canada may be higher than the estimate of 100 to 900 leatherbacks per summer reported by Shoop & Kenney (1992) for a much larger study area along the coast of the northeastern United States.

Moreover, abundance estimates based on aerial or shipboard surveys must be considered conservative, as these only include observations of turtles at the surface; they do not account for those turtles present at various depths (Shoop & Kenney, 1992). Given the lack of offshore aerial survey data and fishery bycatch data on leatherbacks in Atlantic Canada, leatherback population size and trends in this area have yet to be determined.

2.7 Biological Limiting Factors

A number of biological (and behavioural) factors affect leatherback turtles by limiting their potential for population growth. These limiting factors have been grouped into those observed in the marine environment, and those that exist in the nesting beach habitat.

2.7.1 Marine environment

Leatherbacks depend on prey with very little nutritive content and since this species' diet of jellyfish is high in water and low in organic content, they must consume large quantities of food (Lutcavage, 1996) to fulfil their food energy requirements. This is the only known biological limiting factor in Canadian waters.

2.7.2 Nesting beach habitat

Leatherbacks prefer to nest on exposed, open beaches, adjacent to deep water and typically unprotected by fringing reefs. In some years large numbers of nests on such beaches are lost to flooding and erosion (e.g., Whitmore & Dutton, 1985; Leslie et al., 1996). In addition, the leatherback turtle is unique in producing numerous yolkless eggs in each clutch for which a selective advantage remains to be identified. The yolkless eggs may not have a function and thus may be a potential cost to reproduction (Rostal et al., 1996).

Further, Leatherbacks are thought to be a long-lived species but life expectancy is unknown; the age at maturity is estimated at 5-14 years (Zug & Parham, 1996). This, coupled with a 2-3 year interval between nestings (Hughes, 1996), may limit the ability of populations to rebound in times of low survival rates.

2.8 Threats

Researchers have observed a decline of over 70% in the leatherback turtle population on its nesting beaches. While there are known (and probably unknown) threats to leatherbacks in migratory and feeding habitat, these are not well understood. Threats occur both in nesting habitat and at sea. Because this strategy focuses on those known and potential threats that occur in Atlantic Canadian waters, it more specifically addresses threats that occur at sea.

2.8.1 Threats in the Marine Environment

Entanglement in fishing gear

Leatherback turtles are incidentally captured in nets and entangled in lines in fisheries operating in pelagic and coastal foraging areas and in migratory corridors. Of all the Atlantic sea turtle species, leatherbacks seem to be the most vulnerable to entanglement in fishing gear such as pelagic longlines, lines associated with fixed pot gear and gillnets, buoy anchor lines, and other ropes and cables (e.g., Chan et al., 1988; Goff & Lien, 1988; NMFS, 1992; Cheng & Chen, 1997; Godley et al., 1998).

Interactions between leatherback turtles and fishing gear are expected to differ depending on gear type. Although little observer data exist to document leatherback interactions with different gear types in Atlantic Canadian waters, O'Boyle (2001) identifies the gears with high potential for interactions (Table 1).

Incidental interaction of marine turtles in pelagic longlines is evident from observer data for the Canadian pelagic longline fisheries. These fisheries have implemented the broadest observer coverage to date among Atlantic fisheries that have been identified as posing a risk of interaction with leatherback sea turtles.

Turtle interactions do not appear to occur in Canadian pelagic longline fisheries targeting shark (Javitech 2003C), but are well documented in longline fisheries targeting swordfish and tunas (28 individuals – swordfish 2001; 33 individuals – swordfish 2002; 4 individuals – offshore tuna 2002). During a two-year programme of enhanced observer coverage levels of 20%, live release was observed in all cases for leatherback turtles in the swordfish fisheries. Similar results were observed in the offshore tuna fishery where observer coverage levels were 100% in 2002.

From observations in the swordfish fishery, hooks and gangion line remained attached to turtles in 48.8% of all cases in 2001 and 74.5% of all cases in 2002. Just hooks remained attached in 5.6% of all cases in 2001 and 24.1% of all cases in 2002. All hooks and gangion line were removed from 33.3% of all cases in 2001 and 1.4% of all cases in 2002. In all of the above cases, post-release mortality is not known (Javitech 2002, 2003A and 2003B).

Unfortunately, no observer information exists regarding interactions between the leatherback turtle and fixed gear. However, valuable information is available through strandings. The Nova Scotia Leatherback Turtle Working Group  reported 87 records of stranded leatherbacks from 1995-2002 – turtles entangled in fixed fishing gear and turtles found floating dead in shelf waters off Atlantic Canada.

Of the 87 records, 74% provided direct or indirect evidence of leatherbacks interacting with fixed fishing gear and 62% were associated with specific types of gears. Snow crab, rock crab, inshore lobster, offshore lobster and whelk fisheries were associated with 29% of the records, 22% of the records involved mooring or buoy lines associated with bottom gill nets, bait nets and pound nets of other fish traps. Three percent were associated with vertical lines in the groundfish longline gear.

Leatherback turtles are also entangled in U.S. Atlantic waters. For example, 92 leatherbacks were entangled in fixed pot gear from New York through Maine for the period 1990-2000 (Dwyer et al., 2002). Additional leatherbacks are stranded with line wraps or evidence of prior entanglement (Dwyer et al, 2002). Further, leatherback interactions have been observed in the shrimp trawl and other bottom trawl fisheries. Historically, interactions were observed in the drift gillnet fishery for swordfish. However, in January 1999, the U.S. National Marine Fisheries Service (NMFS) issued a Final Rule to prohibit the use of driftnets (i.e. permanent closure) in the North Atlantic swordfish fishery (50 CFR Part 630).

Although NMFS promulgated regulations requiring the use of turtle excluder devices (TEDs) in shrimp trawl fisheries in 1990, Epperly et al. (2002) in a review of sea turtle stranding data, found that the TED openings were much too small to exclude leatherbacks and larger loggerhead and green turtles. In 2003 NMFS amended the regulations to require larger TED openings in U.S. Atlantic and Gulf of Mexico waters. In addition to the TED regulations, the U.S. also established a leatherback turtle Conservation Zone in 1995 to restrict trawl activities on the Atlantic coast during periods when leatherbacks are concentrated.

The susceptibility of leatherbacks to entanglements may result from their large body size, long pectoral flippers and soft shell. Entanglement of leatherbacks in lines or cable can result in serious injuries, infection, necrosis or death. These entangled turtles are generally limited in their ability to feed, dive, breathe or perform any other behaviour essential to survival (Balazs, 1985).

Collisions

While no incidences of collisions with boats are documented in Atlantic Canada, they have been known to occur in some areas of the U.S. and may have an impact on the leatherback turtle population that also uses Canadian waters. In areas where recreational boating, commercial fishing and ship traffic are concentrated, propeller and collision-related injuries may represent a source of mortality (NMFS, 1992). However, in situations where there is evidence of a collision, it is difficult to infer whether the collision itself led to the death of the turtle in question, or if the turtle was hit after it died of other causes. Leatherback turtles are known to bask at the surface for extended periods of time when foraging in temperate waters and, therefore, may be vulnerable to collisions with marine traffic.

Marine Pollution

The effect of marine pollution on sea turtles is not well quantified, and therefore the magnitude of pollution-related mortality is unknown. Leatherback sea turtles may be more susceptible to marine debris ingestion than other turtle species due to their pelagic existence and the tendency of floating debris to concentrate in convergence zones that adults and juveniles use for feeding areas and migration (Lutcavage et al., 1997; Shoop & Kenney 1992).

Leatherbacks are known to ingest a variety of anthropogenic marine debris, including plastic bags, balloons, plastic and Styrofoam pieces, tar balls, plastic sheeting, and fishing gear (e.g., Sadove, 1980; Hartog &Van Nierop, 1984; Lucas, 1992; Starbird, 2000). Ingestion of such materials may interfere with metabolism or gut function and lead to blockages in the digestive tract, which could result in starvation or in the absorption of toxic byproducts (Plotkin & Amos, 1989).

Leatherbacks may serve as an indicator of the degree of contamination of the oceanic food web by bio-accumulating substances such as heavy metals and polychlorinated biphenyls (PCBs) found in plankton-feeding jellyfish (Davenport & Wrench 1990). Metal and PCB levels in the leatherback are expected to represent a biomagnification of concentrations found in their prey; however, to date, tissue samples derived from leatherbacks in European waters have not revealed evidence of significant chemical contamination (Davenport et al., 1990; Godley et al., 1998).

Acoustic disturbances

Little is known about the hearing ability of the leatherback turtle and its response to acoustic disturbance. Studies involving adult green, loggerhead and Kemp's ridley turtles suggest that sea turtles detect sounds in the low frequency sound range, with the greatest hearing sensitivity between 250-700 Hz (Ridgway et al., 1969; Lenhardt et al., 1983; Bartol et al., 1999).

The effects of exposure to increased noise, based largely on studies involving marine mammals, may include habituation, behavioural disturbance (including displacement), temporary or permanent hearing impairment, acoustic masking, and mortality (Richardson el al., 1995). Studies on sea turtles have shown that certain levels of exposure to low frequency sound may cause displacement from the area near the sound source and increased surfacing behaviour (O'Hara & Wilcox, 1990; Lenhardt et al., 1983). This raised the concern that turtles may be displaced from preferred foraging areas (e.g., O'Hara & Wilcox, 1990; Moein et al., 1994).

There are a range of sources of anthropogenic noise in the marine waters of Atlantic Canada that produce underwater sounds within the frequency range detectable by sea turtles. These include oil and gas exploration and development, shipping, fishing, military activity, underwater detonations, and shore based activities (Davis et al., 1998; Greene & Moore, 1995; Lawson et al., 2000). Concerning the exposure to seismic airguns used in exploration, studies to date describe behavioural responses such as; increased swimming speed, increased activity, change in swimming direction and avoidance (DFO, 2004). Startle responses and erratic swimming behaviour was observed by McCauley et al. (2000).  A study by Moein et al., (1994), noted a temporary reduction in hearing capability and temporarily increased physiological parameters (e.g., glucose, white blood cells and creatinine phosphokinase) which is suggestive of damaged tissues or altered physiology. Overall, based on the available information, it is considered unlikely that sea turtles are more sensitive to seismic operations associated with oil and gas exploration than cetaceans or some fish (DFO, 2004). Seismic operators currently use mitigation techniques, such as "ramp-up" procedures to encourage species such as marine mammals to move away from survey areas, and use "shut down" procedures when a species is identified as too close to survey. However, mitigation focused on detection are expected to be less effective for turtles given that they are more difficult to identify both visually and acoustically. Noise from offshore hydrocarbon production platforms and exploration drilling generally tend to be of low frequency (<500 Hz) (Richardson et al., 1995); however there are no published studies on the potential impacts of production or drilling operations on sea turtles. Sea turtles may react to noise from vessel traffic and helicopter overflights with a startle response (NRC, 1990; NOAA, 2002). Although it is assumed that turtles close to the surface can hear aircraft noise and may subsequently change their behaviour, there are no published studies to confirm this (NOAA, 2002).

2.8.2 Threats to the Nesting Environment

Poaching

The harvest of nesting adult females and their eggs for consumption or other uses continues to be a serious threat to leatherbacks throughout much of their range. The loss of nesting adults can lead to local extirpations, while the collection of eggs reduces the number of hatchlings available for future recruitment. To protect eggs from harvest, a number of conservation programs have developed hatcheries. While this may increase the total number of hatchlings released into the wild, artificial incubation - which is typically done at lower ambient beach temperatures - may result in the production of increased numbers of males (Morreale, et al.,1982; Mrsovsky, 1982; Dutton et al., 1985). The long-term recovery implications of this altered sex ratio have not been quantified.

While leatherback meat is considered unpalatable by most, poaching of free-swimming and nesting turtles for meat and/or oil does occur in some areas, including the British Virgin Islands, Dominican Republic, Jamaica, Puerto Rico and the U.S. Virgin Islands (Fleming 2001). A larger, more widespread problem is the collection of leatherback eggs for sale in local and/or foreign markets in the aforementioned countries as well as the Bahamas (Fleming 2001).

Coastal Construction

Coastal development and the resultant beach armouring (seawalls, revetments, riprap, sand bags, groins, and sand fences) put in place to protect upland structures from erosion can interfere with access to suitable nesting sites during construction, throughout the duration of the armouring and when structures deteriorate. Erosion associated with hard armouring structures also leads to the loss of nesting habitat (NMFS, 1992). Soft armouring such as beach nourishment can result in beaches unsuitable for nesting due to compaction or severe scarping and may also result in an altered physical nesting environment that can adversely impact hatchling development and hatching success.

Artificial Light

Artificial lighting associated with coastal development, construction activities and roads can result in the disorientation of nesting adults and emerging hatchlings, resulting in failed nesting attempts and mortality of hatchlings. Adult females may avoid nesting on beaches with intense artificial lighting or ambient glow. When they do successfully nest on these beaches, hatchlings are attracted toward the artificial light source, which disrupts their natural sea finding behaviour, resulting in stress, dehydration, and predation (Witherington, 1992; Witherington & Bjorndal, 1991).

Climate Change

According to Davenport (1997), global warming is predicted to have deleterious effects on marine turtles, as it could potentially influence temperature-dependent sex determination. It can also be argued that increased hurricane activity associated with global climate change could result in increased nest loss due to amplified wind and wave erosion on leatherback nesting beaches. Lastly, alterations in ocean current patterns may accompany climate change, thereby affecting the migration and dispersal of marine turtles (Davenport, 1997).

Other Potential Threats

Other important threats to nesting habitats include: beach erosion, nest predation, beach driving, beach cleaning, beach mining, and exotic vegetation.

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.