Marine Resources Assessment for the Marianas Operating ... - SPREP

AUGUST 2005 FINAL REPORT
migrations following depth contours for hundreds, even thousands, of kilometers (Morreale et al.
1996; Hughes et al. 1998). Using satellite telemetry, Morreale et al. (1996) determined that postnesting
female leatherbacks in the Pacific Ocean share identical migrational pathways. However, the
timing and routing of their reproductive migrations in the Pacific Ocean are still unknown. It is believed
that migratory corridors exist along the west coasts of the U.S. and Mexico and in the pelagic zone
surrounding the Hawaiian Islands (Nitta and Henderson 1993; NMFS and USFWS 1998c).
There are few quantitative data available concerning the seasonality, abundance, or distribution of
leatherbacks in the central North Pacific Ocean. The leatherback is not typically associated with
insular habitats, such as those characterized by coral reefs, yet individuals are occasionally
encountered in deep ocean waters near prominent archipelagos such as the Hawaiian Islands (Eckert
1993). Leatherbacks are regularly sighted by fishermen in Hawai’i’s offshore waters, generally
beyond the 183 m contour, and especially at the southeastern end of the island chain and off the
north coast of Oahu (Nitta and Henderson 1993; Balazs 1995, 1998). Leatherbacks encountered in
these waters, including those caught incidental to fishing operations, may represent individuals in
transit from one part of the Pacific Ocean to another (NMFS and USFWS 1998c). Leatherbacks
apparently have a wide geographic distribution throughout the region where the Hawai’i-based
longline fishery operates, with sightings and reported interactions commonly occurring around
seamount habitats located above the Northwestern Hawaiian Islands (from 35° to 45°N and 175° to
180°W) (Skillman and Balazs 1992; Skillman and Kleiber 1998).
Some of the world’s largest nesting populations of leatherback turtles are found in the Pacific Ocean;
however, nesting is not likely to occur on Pacific beaches under U.S. jurisdiction (NMFS and USFWS
1998c). The Pacific coast of Mexico is generally regarded as the most important leatherback breeding
ground in the world. Roughly one-half of the world’s leatherback population nests there (Pritchard
1982). Other principal nesting sites in the Pacific basin include beaches in Malaysia, Indonesia,
Papua New Guinea, and Costa Rica (Spotila et al. 1996). Leatherbacks generally do not nest in the
insular Pacific and are not known to nest at Guam and the CNMI (Eckert 1993). It is not known
whether leatherbacks encountered in the insular Pacific Ocean come from eastern or western Pacific
nesting beaches. However, a genetic analysis of 14 individuals captured in the Hawai’i-based longline
fishery revealed that a majority (12) came from the western Pacific nesting population (HDLNR 2002).
Information Specific to Marianas MRA Study Area―Of the three sea turtle species that have
been sighted around Guam and the CNMI during marine surveys, the leatherback turtle is the
least common (NMFS and USFWS 1998c). This species is occasionally encountered in the deep,
pelagic waters of the Marianas archipelago, although only a few occurrence records exist (Eckert
1993; Wiles et al. 1995). In 1978, a 113-kg leatherback was rescued from waters southeast of
Cocos Island, Guam (Eldredge 2003). From 1987 to 1989, divers reported seeing leatherbacks in
the waters off Harnom Point, Rota; however, none have been seen in the area in recent times
(Michael 2004). Leatherbacks do not nest at any of the islands in Micronesia.
As a result, leatherback turtles are not expected to occur in coastal (i.e., shelf) waters around any
of the islands of the Marianas chain. In oceanic waters beyond the shelf break, leatherback
occurrence is low/unknown due to a lack of survey effort over those waters, the weak association
between leatherbacks and insular regions of the North Pacific Ocean, and the belief that any
leatherbacks encountered in the area would be transient individuals (Eckert 1993; Kolinski 2001).
These occurrence patterns hold for all seasons (Figure C-6).
Behavior and Life History—The wide range of leatherbacks is a result of their highly evolved
thermoregulatory capabilities. Leatherbacks can maintain body core temperatures well above the
ambient water temperature. For example, a leatherback caught off Nova Scotia, Canada had a body
temperature of 25.5°C in water that was 7.5°C (Frair et al. 1972). A variety of studies have shown that
leatherbacks have a range of anatomical and physiological adaptations that enable them to regulate
internal body temperatures (Mrosovsky and Pritchard 1971; Greer et al. 1973; Neill and Stevens
1974; Paladino et al. 1990).
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