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Recovery Strategy for Leatherback Turtles
2.5 Nationally Significant Populations
Leatherback turtles frequenting Pacific Canadian waters are considered to be genetically distinct from the turtles occurring in Atlantic Canadian waters. This distinction was first suggested by Pritchard (1979) and confirmed through analysis of sequence divergence in mitochondrial DNA by Dutton et al. (1999). The Pacific stock comprises (at least) two reproductively isolated populations, namely the Western and Eastern Pacific populations described in section 2.2.1. Each of these may warrant recognition as a nationally significant population, but it is not yet known whether turtles from the Eastern Pacific population frequent Pacific Canadian waters. Both populations are considered in this Recovery Strategy.
2.6 Population Status and Trends
Population estimates for leatherbacks are based on numbers of nesting females, hence are relative rather than absolute and may be affected by skewed sex ratios. Nevertheless, the trends are clear. When both Pacific and Atlantic stocks are considered, the global number of nesting female leatherbacks fell from an estimated 115,000 in 1980 (Pritchard 1982) to 34,500 by 1995 (Spotila et al. 1996). This alarming decline is unevenly distributed, with nesting falling off more severely in Pacific populations, where some beaches had annual adult mortality as high as 33% (Spotila et al. 2000). Large numbers of turtles were killed in high seas fishing operations (Wetherall 1993; Eckert and Sarti 1997), while egg harvest, the killing of nesting females and nesting beach habitat destruction were also important factors (Chan and Liew 1996). Nesting activity in the Atlantic may be more stable, but still has periods of increase and decrease which make the trends more difficult to decipher.
The leatherback turtle is listed by IUCN as Critically Endangered (80% reduction in numbers in ten years or three generations). It is also listed under CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora), an international agreement that ensures trade in wild animal and plant species does not threaten their survival, and in Appendix 1 of the Convention on Migratory Species, which classifies the species as endangered.
The following sections present status and trends for Eastern and Western Pacific populations; the latter may be more directly relevant to Canadian waters.
Eastern Pacific nesting populations
Until recently the largest known population of leatherbacks nested on the Pacific coast of Mexico. These turtles, whose known forage grounds include areas to the south off Peru and Chile, have severely declined in recent years. Mexiquillo Beach, an index beach on the Mexican coast, has seen a decline in nests from 5,000 in the 1980s to less than 100, and this decline is believed representative of the entire Eastern Pacific population (Sarti 2002). The 2001-2002 nesting season was the worst in twenty years, both in terms of numbers of females and numbers of nests. The decline is believed due primarily to egg harvest and accidental capture in fisheries.
Western Pacific nesting populations
The Western Pacific population of leatherbacks, which is the presumed source of most of the adults foraging off Pacific Canada, includes populations that nest in Malaysia, Indonesia (Papua), Papua New Guinea and the Solomon Islands, with lesser contributions from beaches in Vanuatu, Fiji, China and Australia. The most important sites are Indonesia and Papua New Guinea. Unfortunately the population trends are not as well known as for the Eastern Pacific populations, and published reports are few and conflicting.
Terengganu, one of the east coast states of peninsular Malaysia, was once a major leatherback nesting area but has declined drastically. The Rantau Abang population has decreased from about 10,000 nests in the 1950s to fewer than 20 in recent years (Liew 2002). The declines appear to have occurred in two waves, one coinciding with rapid development of the fishing industry in Terengganu in the mid-1970s, and the second with introduction of the Japanese high seas squid driftnet fishery in the North Pacific in 1978. The nesting beaches were also subject to severe overharvest of eggs (often approaching 100%) since the 1940s. Since these events, the decline has averaged 16% annually. Only two females were recorded nesting in 1994 (Chan and Liew 1996).
The other major nesting sites in the Western Pacific are on beaches in Papua (formerly Irian Jaya), a part of the Indonesian archipelago that shares a land mass with New Guinea. In the 1980s smaller areas of nesting in Indonesia occurred on western Sumatra and southeastern Java (Suarez and Starbird 1996). Most of the turtles in Papua nest at Jambursba Medi Beach (Hitipeuw 2002; Putrawidjaja 2000), where over 80% of the nests are affected by poaching, predation by wild pigs, and erosion (Hitipeuw 2002; Suarez and Starbird 1996). The number of leatherback clutches deposited at Jambursba Medi beach has been reported to be stable between 1993 and 1996 (Hitipeuw 2002; Dermawan 2002); however, the long term trends are unclear and possibly declining (Hitipeuw 2002).
2.6.2 Pacific Canada
Information on sightings in B.C. coastal waters is extremely limited and it is not currently possible to draw any conclusions on population trends.
2.7 General Habitat requirements
Habitats that need to be considered include nesting, breeding and foraging habitats. Very little is known about distribution patterns in foraging habitats and migration routes and about the years between hatching and sexual maturity.
In nesting habitat, females require a sandy beach with a deep ocean approach and few obstructions like rock or coral (Pritchard 1971; Ernst and Barbour 1989). Habitat requirements for hatchlings and juveniles appear to be almost exclusively tropical until the turtles exceed 100 cm in carapace length (Eckert 2002a). Large juveniles and subadults probably share habitats with adult leatherbacks.
Adults frequent cooler waters, including the continental shelves off Canada and the northeastern United States (Shoop and Kenney 1992). They follow oceanic frontal systems where productivity is high and results in high concentrations of prey (Lutcavage 1996). The coast of British Columbia provides foraging habitat; however, no studies have been done to verify specific foraging habitat areas important to leatherback turtles. Therefore it is impossible to identify either the habitat currently occupied by leatherback turtles in Pacific Canadian waters, or the amount of critical habitat needed to recover and support a viable population.
2.7.1 Critical Habitat
SARA, under section 2, defines critical habitat as 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.” It is difficult to define critical habitat for turtles, as each life stage has different requirements distributed over large ocean basins. Although the knowledge base to help determine critical habitat is increasing with new research projects, at this time it is not possible to identify critical habitat for this species. As set out in the Act, if information is inadequate to identify critical habitat within the recovery strategy, a schedule of studies must be prepared. This schedule, once implemented, will yield new information that will help to identify the species’ critical habitat in the future.
The schedule of studies, which is essentially a list of habitat research projects, identified for the pacific leatherback turtle can be found in Appendix 1. Upon completion of these projects, it is hoped that the results will allow Fisheries and Oceans Canada to be able to identify critical habitat for this species in an action plan.
2.8 Ecological role
Adult leatherbacks feed voraciously on jellyfish and other soft-bodied pelagic invertebrates that consume large quantities of zooplankton and fish larvae. They thus occupy an important position in the marine food chain. It may be assumed that leatherbacks play an important ecosystem role, helping maintain the balance between the numbers of their prey and the organisms that feed on that prey. They are also important components of terrestrial ecosystems in providing nutrients through unhatched and broken eggs and eggshells, and the eggs themselves are food for terrestrial animals who carry the nutrients inland (Eckert 2002c).
2.9 Social and economic considerations
There is very limited directed fishery on adult leatherbacks anywhere in the world as the flesh is not generally considered palatable. However, the people of the Kai Kecil Islands in Indonesia have a ritual hunt for adult leatherbacks (Suarez and Starbird 1996). Many people that live near nesting areas eat and sell leatherback eggs.
Leatherbacks probably do not occur close enough to land or in sufficient numbers to be of any importance to tourism. Although coastal First Nations are familiar with the animal, very limited anecdotal information from Clayoquot Sound, centrally located in the Pacific Canadian foraging range, suggests no evidence of any special use or significance (Webster 2002, pers. comm.). If an ethnographic study of the significance of leatherbacks to coastal First Nations were to be done it would need to include groups throughout the known range of sightings.
SARA requires recovery strategies to include “an identification of the species’ critical habitat, to the extent possible, based on the best available information, including information provided by COSEWIC” [SARA, s.41(c)].
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