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

AUGUST 2005 FINAL REPORT
Incubation time from deposition to emergence is approximately 55 days (Eckert 1993; NMFS and
USFWS 1998d).
Relatively few studies have investigated the diving behavior of olive ridley turtles. In the eastern
tropical Pacific, olive ridleys have been shown to make more frequent submergences and spend
more time at the surface during the day than at night (Beavers and Cassano 1996). As a result,
nighttime dives are longer in duration (reaching a maximum of 95.5 min). Olive ridleys have been
observed diving to depths of 300 m, although only about 10% of their time is spent at depths greater
than 100 m (Eckert et al. 1986; Polovina et al. 2003).
♦ Leatherback Turtle (Dermochelys coriacea)
Description—The leatherback turtle is the largest living sea turtle. These turtles are placed in the
family Dermochelyidae, a separate family from all other sea turtles, in part because of their unique
carapace structure. A leatherback turtle’s carapace lacks the outer layer of horny scutes possessed
by all other sea turtles; instead, it is composed of a flexible layer of dermal bones underlying tough,
oily connective tissue and smooth skin. The body of a leatherback is barrel-shaped and tapered to the
rear, with seven longitudinal dorsal ridges, and is almost completely black with variable spotting. All
adults possess a unique spot on the dorsal surface of their head, a marking that can be used by
scientists to identify specific individuals (McDonald and Dutton 1996). Adult carapace lengths range
from 119 to 176 cm with an average around 145 cm (NMFS and USFWS 1998c). Adult leatherbacks
weigh between 200 and 700 kg. Surveys of nesting leatherbacks in the Atlantic and Pacific Oceans
indicate gene flow between rookeries within ocean basins and also that western Atlantic and eastern
Pacific leatherbacks shared a common ancestor in recent evolutionary history (Dutton et al. 1994).
Status—Leatherback turtles in the Pacific Ocean are highly endangered and may become extinct in
the next several decades if current trends in mortality persist. Lewison et al. (2004) estimated that
more than 50,000 leatherbacks were taken as pelagic longline bycatch in 2000 and that thousands of
these turtles die each year from longline gear interactions in the Pacific Ocean alone. Leatherbacks
are seriously declining at most Pacific Ocean rookeries, including Indonesia, Malaysia, and Mexico
(NMFS and USFWS 1998c). No attempts have been made to assess the status of foraging
populations. The most recent estimate of the worldwide leatherback population was 34,500 nesting
females, with a lower and upper limit of 26,200 and 42,900 nesting females (Spotila et al. 1996).
Habitat Preferences—There is limited information available regarding the habitats utilized by early
juvenile leatherbacks because this age class is entirely oceanic (NMFS and USFWS 1998c).
However, it is known that early juveniles are generally restricted to waters greater than 26°C and that
they likely do not associate with Sargassum or other flotsam, as is the case for the other five sea
turtle species found in U.S. waters (NMFS and USFWS 1998c; Eckert 2002).
Late juvenile and adult leatherback turtles are known to range from mid-ocean to the continental shelf
and nearshore waters (Schroeder and Thompson 1987; Shoop and Kenney 1992; Grant and Ferrell
1993). Juvenile and adult foraging habitats include both coastal feeding areas in temperate waters
and offshore feeding areas in tropical waters (Frazier 2001). The movements of adult leatherbacks
appear to be linked to the seasonal availability of their prey and the requirements of their reproductive
cycle (Collard 1990; Davenport and Balazs 1991). During their oceanic migrations, leatherbacks
prefer convergence zones and upwelling areas in the open ocean, along continental margins, or near
large archipelagos (HDLNR 2002).
Distribution—The leatherback turtle is distributed circumglobally in tropical and warm-temperate
waters throughout the year and into cooler temperate waters during warmer months (Ernst et al.
1994). Leatherbacks in the North Pacific Ocean are broadly distributed from the eastern tropical
Pacific region to as far north as Alaska, where 19 occurrences have been documented since 1960
(Eckert 1993; Wing and Hodge 2002). This species migrates further and moves into cold waters more
than any other sea turtle species (Bleakney 1965; Lazell 1980; Shoop and Kenney 1992). This
species is also the most oceanic and most wide-ranging of sea turtles, undertaking extensive
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