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

AUGUST 2005 FINAL REPORT
are located in close proximity to nearshore reefs or rocky areas used for resting (Balazs 1980; Ernst
et al. 1994). Green turtles can feed as deep as their primary food source will grow. In Hawai’i, green
turtles are known to forage and rest in waters as deep as 20 to 50 m (Brill et al. 1995). In the Mariana
Islands, resting areas usually occur just outside of the fringing reef in caves and depressions
associated with the reef face. Resting areas can also be found in channels and other structures
associated with hard substrate. These areas tend to be located at water depths between 10 and 40 m
(NMFS 1998).
Distribution—Green turtles are distributed worldwide in tropical and subtropical waters with
temperatures above 20°C. The most important nesting and feeding grounds lie within the tropics
(Pritchard 1997). In U.S. Pacific waters, green turtles are regularly found off the coasts of southern
California, the Hawaiian Islands, American Samoa, Guam, the CNMI, and several of the
unincorporated U.S. territories such as Wake Island and Palmyra Atoll (NMFS and USFWS 1998a).
During warm spells, adult and juvenile green turtles have been sighted in waters as far north as
Alaska, where 15 occurrences have been documented since 1960 (Eckert 1993; Wing and Hodge
2002). This species occurs throughout the year in tropical waters such as those off of Guam and the
CNMI.
As they grow, juvenile green turtles are known to move through a series of developmental feeding
habitats, which are often separated by thousands of kilometers (Hirth 1997). Mixed-stock analyses on
juvenile foraging populations have revealed that developmental feeding habitats likely contain green
turtles from multiple stocks. Green turtles captured on foraging grounds off Baja California and in San
Diego Bay have shown physical and genetic characteristics of both the Mexican Pacific and Hawaiian
breeding populations (Dutton and McDonald 1990; Nichols et al. 2000a). However, little is known
regarding the stock compositions of juvenile foraging populations in the insular Pacific Ocean.
Adult green turtles are known to undertake extensive migrations, the longest of which are between
their foraging habitats and nesting beaches. Long-distance reproductive migrations have been noted
for green turtles nesting at a number of locations in the Pacific Ocean including the Northwestern
Hawaiian Islands, Taiwan, Hong Kong, American Samoa, and Guam (Balazs 1976, 1980, 1983;
Cheng 2000; Chan 2003; Craig et al. 2004; Gutierrez 2004). From June through November 2000,
biologists from the Guam Division of Aquatic and Wildlife Resources (DAWR) satellite-tracked an
adult green turtle’s post-nesting movements from its nesting beach at Hagåtña, Guam to its feeding
grounds in the southern Philippines, a trip of nearly 3,500 km (Figure 3-4).
Green turtles nest throughout the Pacific Ocean, with active nesting colonies in the eastern, central,
and western regions. Major nesting colonies in the eastern Pacific are located in Mexico and the
Galapagos Islands, while high-density nesting sites in the western Pacific are found primarily in
eastern Australia (along the Great Barrier Reef). Green turtle nesting populations in the insular Pacific
Ocean are relatively small. The largest nesting colony in the insular Pacific occurs at French Frigate
Shoals in the Northwestern Hawaiian Islands, where about 200 to 700 females nest each year.
Elsewhere in the U.S. Pacific, low-level nesting (less than ten individuals per year) occurs at
scattered locations in the CNMI, Guam, and American Samoa (NMFS and USFWS 1998a). At least
24 green turtle nests were documented during comprehensive beach surveys on Tinian in 1995 and
six green turtle nests were documented during similar surveys on Saipan in 1999 (Kolinski et al.
1999; Pultz et al. 1999).
Information Specific to Marianas MRA Study Area―Green turtles are by far the most abundant
sea turtle found throughout the Marianas archipelago. Aerial surveys conducted by the Guam
Division of Aquatic and Wildlife Resources (DAWR) indicate the presence of a year-round
resident population in Guam’s nearshore waters (NMFS 1998). From 1989 to 1991, green turtles
accounted for at least 65.8% of all aerial survey sightings around the island (Davis n.d.).
Aggregations of foraging and resting green turtles are often seen in close proximity to Guam’s
well-developed seagrass beds and reef flats, which are found in Cocos Lagoon, Apra Harbor,
along Tarague Beach and Hilaan, in deeper waters south of Falcona Beach, and at several other
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