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

AUGUST 2005 FINAL REPORT
Loggerhead nesting in the North Pacific Ocean occurs between April and August, when nearshore
water temperatures reach 20°C and above (NMFS and USFWS 1998e). Females from the Japanese
nesting stock nest at least three times per season, at about two-week intervals (Eckert 1993).
Loggerhead clutches contain between 60 and 150 eggs and often take about 60 days to incubate.
Dodd (1988) estimated that the global average hatching success for loggerheads is nearly 75%. Adult
females nest at multiple year intervals, with the majority nesting every two years (Frazer 1995).
On average, loggerhead turtles spend over 90% of their time underwater (Byles 1988; Renaud and
Carpenter 1994). Dive-depth distributions compiled by Polovina et al. (2003) in the North Pacific
Ocean indicate that loggerheads tend to remain at depths shallower than 100 m. Routine dive depths
are typically shallower than 30 m, although dives of up to 233 m were recorded for a post-nesting
female loggerhead off Japan (Sakamoto et al. 1990). Routine dives can last from 4 to 172 min (Byles
1988; Sakamoto et al. 1990; Renaud and Carpenter 1994).
♦ Olive Ridley Turtle (Lepidochelys olivacea)
Description—The olive ridley is a small, hard-shelled sea turtle named for its olive green colored
shell. Adults often measure between 60 and 70 cm in carapace length and rarely weigh over 50 kg.
The carapace of an olive ridley turtle is wide and almost circular in shape. The olive ridley differs from
the Kemp’s ridley, the other member of the genus Lepidochelys, in that it possesses a smaller head,
a narrower carapace, and several more lateral carapace scutes (NMFS and USFWS 1998d).
Status—Olive ridleys are classified as threatened under the ESA, although the Mexican Pacific coast
nesting population is labeled as endangered. There has been a general decline in the abundance of
this species since its listing in 1978. Until the advent of commercial exploitation, the olive ridley was
highly abundant in the eastern tropical Pacific, probably outnumbering all other sea turtle species
combined in the area (NMFS and USFWS 1998d). Cliffton et al. (1995) estimated that a minimum of
10 million olive ridleys were present in ocean waters off the Pacific coast of Mexico prior to 1950.
Even though there are no current estimates of worldwide abundance, the olive ridley is still
considered the most abundant of the world’s sea turtles. However, the number of olive ridley turtles
occurring in U.S. territorial waters is believed to be small (NMFS and USFWS 1998d).
Habitat Preferences—Olive ridley turtles typically inhabit offshore waters, foraging either at the
surface or at depth (usually up to 150 m). The habitat preferences of the olive ridley more closely
parallel those of the leatherback rather than those of its relative, the Kemp’s ridley. Olive ridleys and
leatherbacks both occupy oceanic habitats and nest primarily on the Pacific shores of the American
tropics and in the Guianas. Both species also nest in moderate numbers in southern Asia and in very
small numbers elsewhere (e.g., in Australia and on small oceanic islands in the Pacific Ocean)
(NMFS and USFWS 1998d). Polovina et al. (2004) discovered that olive ridleys in the North Pacific
Ocean are found primarily between 8° and 31°N latitude in waters between 23° and 28°C.
Distribution—The olive ridley turtle is a pantropical species, occurring worldwide in tropical and
warm temperate waters. It is by far the most common and widespread sea turtle in the North Pacific
Ocean; individuals regularly occur in waters as far north as California and as far south as Ecuador
(Pitman 1990; NMFS and USFWS 1998d). Further offshore from North and South America, olive
ridley turtles become increasingly uncommon, both at sea and around oceanic islands (Balazs 1995).
Olive ridleys are rare visitors to the insular Pacific Ocean, although they have been recorded in
increasing numbers in Hawai’i over the past few decades (Eckert 1993). Available information
suggests that olive ridleys traverse the oceanic waters surrounding the Hawaiian Islands during
foraging and developmental migrations (Nitta and Henderson 1993).
The second largest nesting population of olive ridleys occurs in the eastern Pacific Ocean, along the
west coasts of Mexico and Central America (NMFS and USFWS 1998d). The largest rookeries in this
region can be found in southern Mexico and northern Costa Rica. Nesting also takes place in the
western Pacific Ocean along the shores of Malaysia and Thailand (Eckert 1993). Female olive ridleys
rarely nest in the insular Pacific Ocean due to their preference for beaches located along continental
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