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

AUGUST 2005 FINAL REPORT
the central Pacific. In the eastern Pacific Ocean, loggerheads have been documented to occur as far
north as Alaska and as far south as Chile (Bane 1992). A large juvenile foraging population is found
off the west coast of Baja California Sur, in a band starting about 30 km offshore and extending out at
least another 30 km (NMFS and USFWS 1998e; Nichols et al. 2000b).
Genetic analyses indicate that nearly all of the loggerheads found in the North Pacific Ocean are born
on nesting beaches in Japan (Bowen et al. 1995; Resendiz et al. 1998). Pacific loggerheads appear
to utilize the entire North Pacific Ocean during the course of development, much like Atlantic
loggerheads use the North Atlantic Ocean. There is substantial evidence that both stocks make two
separate transoceanic crossings. The first crossing (west to east) is made immediately after hatching
from the nesting beach, while the second (east to west) is made upon reaching either the late juvenile
or adult life stage. In the North Atlantic Ocean, hatchlings born on beaches in the western Atlantic
swim with the North Atlantic Gyre system in order to reach developmental habitats in the eastern
Atlantic (around the Azores and Madeira) (Bolten et al. 1998). In the North Pacific Ocean, hatchlings
born on beaches in the western Pacific swim with the NPSG system in order to reach developmental
habitats in the eastern Pacific (off southern California and Mexico) (Polovina et al. 2000). Unlike the
case in the eastern Atlantic, where nesting grounds actually do exist (e.g., in the Mediterranean Sea
along the coast of Greece), all juvenile loggerheads found in the eastern Pacific must eventually
return to the western Pacific in order to reproduce. Nichols et al. (2000b) have concluded that
loggerhead turtles are highly capable of transpacific migration and that the band of water between
25°N and 30°N, also known as the Subtropical Frontal Zone, may be an important migratory corridor
for loggerheads returning to the western Pacific.
Major nesting grounds are located in warm, temperate and subtropical regions, with some scattered
nesting in the tropics. The world’s largest loggerhead nesting colonies are found at Masirah Island,
Oman (bordering the Arabian Sea) and along the Atlantic coast of Florida. Nesting in the Pacific basin
is restricted to the western region (primarily Japan and Australia). There is no loggerhead nesting on
Pacific beaches under U.S. jurisdiction (NMFS and USFWS 1998e).
Information Specific to Marianas MRA Study Area—There are no sighting, stranding, or nesting
records for loggerhead turtles around Guam and the CNMI. The nearest occurrences of this
species are from the waters off Palau and the Philippines (NMFS and USFWS 1998d; Sagun et
al. 2005). This species is more apt to be found in temperate waters of the North Pacific Ocean
(i.e., north of 25°N) off of countries such as Japan, China, Taiwan, northwestern Mexico, and the
southwestern U.S. including Hawai’i (NMFS and USFWS 1998e; Polovina et al. 2001, 2004).
However, Guam and the CNMI are identified as being within the species’ overall range (USFWS
2005). Also, the westward flowing current of the NPSG system, which late juvenile stage
loggerheads use when returning to the western Pacific, passes through the Marianas region
(Pickard and Emery 1982; Polovina et al. 2000). As a result, the occurrence of the loggerhead
turtle is low/unknown throughout the year in all oceanic waters of the study area and vicinity
located beyond the shelf break. Since loggerhead occurrences in the waters off Guam and the
CNMI would most likely involve transient individuals, occurrence is not expected in coastal (i.e,
shelf) waters around any of the islands in the study area and vicinity (Figure C-4).
Behavior and Life History—The diet of a loggerhead turtle changes with age and size. The gut
contents of early juveniles found in masses of Sargassum contained parts of Sargassum,
zooplankton, jellyfish, larval shrimp and crabs, insects, and gastropods (Carr and Meylan 1980;
Richardson and McGillivary 1991; Witherington 1994). Late juvenile loggerhead turtles are
omnivorous, foraging on pelagic crabs, mollusks, jellyfish, and vegetation captured at or near the
surface (Dodd 1988). Off Baja California Sur, the distribution of juvenile loggerheads coincides with
that of a large population of pelagic red crabs (Pleuroncodes planipes) (NMFS and USFWS 1998e).
This indicates that juvenile loggerheads in the eastern Pacific Ocean are probably feeding on dense
concentrations of this highly abundant crustacean. Adult loggerheads are generally carnivorous,
foraging on benthic invertebrates in nearshore waters. However, fish and plants are also taken on
occasion (Dodd 1988).
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