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

AUGUST 2005 FINAL REPORT
CNMI Division of Fish and Wildlife (DFW), Guam DAWR, and USFWS satellite-tagged three adult
female green turtles on their nesting beaches at Tinian. This project was implemented to further
study the movements and migrations of green sea turtles from waters and beaches that are
owned and leased by the Navy on and around Tinian (Kessler and Vogt 2002).
At FDM, four green turtles were observed at the northern end of the island during Navysponsored
marine tow and SCUBA surveys in 2003 (DoN 2004). At least 9 green turtles were
observed during underwater surveys in both 1999 and 2000, while at least 12 green turtles were
observed during surveys in 2001. Most green turtles at FDM have been found either swimming
over the reef platform or resting in holes or caves (DoN 2001). Green turtles are not as abundant
at FDM as they are at some of the larger islands of the Marianas chain. Due to strong current and
tidal conditions, the beaches at FDM are highly unsuitable for nesting (DoN 2004). Also,
seagrasses and benthic algae are relatively sparse around the island and can probably support
no more than a few green turtles at a time (NMFS 1998).
Based on the above information, green turtles are expected to occur year round in all shelf waters
of the study area and vicinity from FDM to Guam (Figure C-2). Around the larger islands of
Tinian, Saipan, Rota, and Guam, green turtle occurrence is concentrated in waters less than 50
m deep. It is at these water depths where green turtle foraging and resting habitats (e.g., fringing
reefs, reef flats, and seagrass beds) are usually found. Beyond the shelf break, green turtle
occurrence is low/unknown. Nesting females and early juveniles are known to move through
oceanic waters of the Marianas chain during their reproductive and developmental migrations
(Gutierrez 2004; Kolinski et al. 2004), but likely do not do so in large enough numbers every year
to warrant those waters being designated as additional areas of expected occurrence.
Behavior and Life History—Late juvenile and adult green turtles feed primarily on seagrasses (e.g.,
turtle grass, manatee grass, shoal grass, and eelgrass), macroalgae, and reef-associated organisms
(Burke et al. 1992; Ernst et al. 1994; Bjorndal 1997). Early juveniles are omnivorous; they feed on a
variety of algae, invertebrates, and small fishes (Ernst et al. 1994). Observations of foraging adult
green turtles in Hawai’i suggest that when benthic age classes feed, they generally lie down on the
sea bottom and, when food is no longer within easy reach, they crawl or swim to a nearby site
(Hochscheid et al. 1999).
Green turtles take between 27 and 50 years to reach sexual maturity, the longest age to maturity for
any sea turtle species (Frazer and Ehrhart 1985). In the insular Pacific Ocean, mature females nest
from one to seven times in a season (one to two is typical) at approximately 10 to 15 day intervals
and reproduce every 2 to 3 years (Balazs 1980). In contrast, over half of all adult male green turtles
return to the breeding grounds every year. During the breeding season, green turtle courtship and
copulation occur in waters proximal to the nesting beach (Owens 1980; NMFS and USFWS 1998a).
The nesting season for green turtles at Guam and the CNMI likely commences in late January and
concludes in August, although recent surveys of nesting beaches on Guam have revealed that green
turtle nesting can occur throughout the year (Kolinski et al. 1999; Pultz et al. 1999; Gutierrez 2004).
At Tinian, green turtle clutch sizes during the 1995 nesting season ranged from 73 to 110 eggs with
an average of 91 eggs per nest (Pultz et al. 1999).
Green turtles typically make dives shallower than 30 m (Hochscheid et al. 1999; Hays et al. 2000);
however, a maximum dive depth of 110 m has been recorded in the Pacific Ocean (Berkson 1967).
The maximum dive time recorded for a juvenile green turtle in Hawai’i is 66 min, with routine dives
ranging from 9 to 23 min (Brill et al. 1995). In Guam’s Agana Boat Basin, a female green turtle stayed
underwater for a record 79 min in order to elude capture by local fishermen (Anonymous 1976).
♦ Hawksbill Turtle (Eretmochelys imbricata)
Description—The hawksbill turtle is a small to medium-sized sea turtle. Adults range between 65
and 90 cm in carapace length and typically weigh around 80 kg (Witzell 1983). Hawksbills are
distinguished from other sea turtles by their hawk-like beaks, posteriorly overlapping carapace scutes,
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