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

AUGUST 2005 FINAL REPORT
margins. In Hawai’i, a single nesting was recorded in September 1985 on the island of Maui, but there
was no successful hatching associated with this event (Balazs and Hau 1986). Since there are no
other known nesting records for the insular Pacific Ocean, this nesting attempt can be considered an
anomaly (NMFS and USFWS 1998d).
Genetic analysis of olive ridleys taken in the Hawai’i-based longline fishery has shown that individuals
from both eastern and western Pacific nesting populations forage in the insular North Pacific Ocean
(Dutton et al. 2000). However, olive ridleys born on eastern Pacific beaches appear to utilize different
oceanic habitats in the region from those used by individuals born on western Pacific beaches. Olive
ridleys of western Pacific origin have been observed in association with major ocean currents of the
central North Pacific, specifically the southern edge of the Kuroshio Extension Current, the NEC, and
the Equatorial Counter Current. These habitats, which are also frequented by Pacific loggerhead
turtles, are probably not used as frequently by olive ridleys of eastern Pacific origin. Instead, olive
ridleys from eastern Pacific nesting populations seem to inhabit waters in the center of the
Subtropical Gyre system. These waters are characterized by warmer temperatures, weaker currents,
greater vertical stratification, and a deeper thermocline (Polovina et al. 2003, 2004). It is unknown
whether olive ridley occurrences in more tropical areas of the insular Pacific Ocean, such as
Micronesia, would include individuals of eastern or western Pacific origin.
Information Specific to Marianas MRA Study Area―Only one olive ridley record exists for Guam
and the CNMI, an alleged capture in the waters near Saipan (Pritchard 1977). The exact location
of this capture, however, is unknown since the turtle was offered for sale in a local souvenir shop.
The nearest in-water sightings of this species have occurred within the Yap and Palau Districts
(Eckert 1993; Pritchard 1995). It is possible that future occurrences could occur in the study area
and vicinity, since olive ridleys are a tropical species, they are the most abundant sea turtles in
the Pacific Ocean, and they have been satellite-tracked through North Pacific waters as far south
as 8°N during developmental migrations (NMFS and USFWS 1998d; Polovina et al. 2004). The
occurrence of the olive ridley turtle is low/unknown throughout the year in all waters surrounding
Guam and the CNMI that are seaward of the shelf break because they are primarily an oceanic
species. In portions of the study area located inside the shelf break (e.g., Apra Harbor, Agat Bay,
nearshore waters around northern Tinian), olive ridleys are not expected to occur (Figure C-5).
Behavior and Life History—The olive ridley turtle is considered omnivorous, eating a variety of
benthic and pelagic prey items including fish, crabs, shrimp, snails, oysters, sea urchins, jellyfish,
salps, fish eggs, and vegetation (NMFS and USFWS 1998d). However, crustaceans and fish serve as
their primary food source. Analyses of stomach contents from olive ridleys caught in the Hawai’ibased
longline fishery indicate that individuals in the central Pacific Ocean feed predominantly on
tunicates (salps and pyrosomas), which are found well below the water surface (Polovina et al. 2004).
At sea, olive ridleys readily associate with floating objects such as logs, plastic debris, and even dead
whales (Arenas and Hall 1992; Pitman 1992). Scientists believe that olive ridleys associate with
flotsam since it provides them with shelter from predation and an abundance of prey items (NMFS
and USFWS 1998d). Olive ridleys in the eastern Pacific are also known to bask at the surface, where
they are often accompanied by seabirds that will roost upon their exposed carapaces and feed on fish
that aggregate beneath them (Pitman 1993).
Unlike all other species of sea turtle except the Kemp’s ridley, the olive ridley is known for nesting en
masse. This type of nesting activity is known as an arribada (Spanish for “arrival”). During an
arribada, hundreds to tens of thousands of breeding olive ridleys congregate in the waters in front of
the nesting beach and then, signaled by some unknown cue, emerge from the sea in unison. There is
currently no estimate of the age at which females begin to reproduce; however, the average length of
nesting adults at Playa Nancite, Costa Rica was 63.3 cm. Nesting occurs throughout the year,
peaking from August to December in the eastern Pacific, from February to July in Malaysia, and from
October to February in Thailand. Females usually nest every one to two years. A typical female
produces two clutches per nesting season, with each clutch averaging 105 eggs. Lone individuals
nest at 15- to 17-day intervals while mass nesters arrive to the nesting beach at 28-day intervals.
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