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

AUGUST 2005 FINAL REPORT
The prevalence of certain species and life stages within the region suggests that the southern portion of
the Marianas arc (including Guam) can be classified as a major foraging habitat for juvenile green turtles
and a minor nesting habitat for adult green turtles. This classification does not diminish the importance of
the nesting habitats on Guam and the CNMI or their potential to support other sea turtle species, as
additional research needs to be conducted in those areas (Kolinski 2001).
Based upon the available occurrence data as well as information from the scientific literature, sea turtles
are expected to occur year round in all waters of the Marianas MRA study area and vicinity located inside
the shelf break, with the highest concentrations of sea turtles occurring in waters less than 50 m deep
around Guam, Tinian, Saipan, and Rota (Figure C-1). Beyond the shelf break, sea turtle occurrence is
low/unknown due to a lack of survey effort in deeper waters and the knowledge that small numbers of
transient individuals travel to, from, or through the study area during developmental or reproductive
migrations (Eckert 1993; Musick and Limpus 1997; Frazier 2001; Gutierrez 2004).
The five sea turtle species known to occur or potentially occurring in the Marianas MRA study area are
listed below in taxonomic order as presented in Table 3-2. Summarized below are the description, status,
habitat preferences, distribution (including location and seasonal occurrence in the Marianas MRA study
area), behavior, and life history for each species.
♦ Green Turtle (Chelonia mydas)
Description—The green turtle (Chelonia mydas) is the largest hard-shelled sea turtle, with adults
commonly exceeding 100 cm in carapace length and 100 kg in weight. As hatchlings, they are only
about 50 mm long and weigh approximately 25 g. Adult carapaces range in color from solid black to
gray, yellow, green, and brown in muted to conspicuous patterns; the plastron is a much lighter yellow
to white. Hatchlings are distinctively black on the dorsal surface and white on the ventral (NMFS and
USFWS 1998a).
The genus Chelonia includes a single species, Chelonia mydas, with two distinct subspecies, the
East Pacific green or black turtle (Chelonia mydas agassizii) and the green turtle (Chelonia mydas
mydas). The East Pacific green turtle is conspicuously smaller, lighter in color, and has a narrower,
more strongly vaulted carapace than the green turtle (NMFS and USFWS 1998a, 1998f). According
to genetic analyses, C. m. agassizii is not a unique lineage relative to other green turtle populations
throughout the world (Bowen and Karl 1997). As a result, the genus Chelonia is considered
monotypic in this report and any mention of “green turtle” will be in reference to the species, Chelonia
mydas, rather than to the two proposed subspecies.
Status—Green turtles are classified as threatened under the ESA throughout their Pacific range,
except for the population that nests on the Pacific coast of Mexico (identified by the NMFS and
USFWS [1998f] as C. m. agassizii), which is classified as endangered. East Pacific green turtles are
recognized as a distinct population segment by the NOAA Fisheries and USFWS and are managed
under a separate recovery plan. With the exception of Hawai’i, green turtle populations are in serious
decline throughout the Pacific Ocean. The primary threats to green turtles at Guam and the CNMI
include direct harvesting of turtles and eggs as well as habitat loss due to rapidly expanding tourism,
including increased coastal development on nesting beaches. There are no estimates of the current
population size of green turtles in the Pacific Ocean (NMFS and USFWS 1998a, 1998f).
Habitat Preferences—In the Pacific Ocean, the early juvenile developmental habitat of the green
turtle is unknown. After hatchlings leave the nesting beach, they apparently move into convergence
zones in the open ocean where they spend an undetermined amount of time in the pelagic
environment (Balazs 2004). Once green turtles reach a carapace length of 35 cm, they migrate to
shallow nearshore areas where they spend the majority of their lives as late juveniles and adults
(Balazs 1980; NMFS and USFWS 1998a).
The optimal habitats for benthic-stage juveniles and adults are warm, quiet, and shallow (3 to 10 m)
waters that possess an abundance of submerged aquatic vegetation (seagrasses and/or algae) and
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