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

AUGUST 2005 FINAL REPORT
area waters located inside the shelf break, including within Guam’s Apra Harbor. However, since
the species is highly endangered and does not occur in large numbers anywhere within the
region, there are no areas of concentrated occurrence around Guam and the CNMI. In deeper
waters beyond the shelf break (e.g., throughout W-517 and in a large portion of the study area
around FDM), the occurrence of the hawksbill turtle is low/unknown. In these waters, the
preferred habitat of the hawksbill is scarce and survey effort is minimal. This occurrence pattern is
due to the species’ great reliance on shallow coastal areas, where coral reefs and live/hardbottom
habitats primarily occur, and the possibility that small numbers of individuals may be making longdistance
migrations through the oceanic waters of the study area on their way to and from areas
of the North Pacific Ocean where they are more abundant, such as Palau.
During aerial surveys between 1989 and 1991, hawksbills represented 13.2% of all sea turtles
sighted around Guam (Davis n.d.). Wiles et al. (1995) indicate that hawksbills are typically found
near river mouths as well as inside Apra Harbor. These are areas where sponges, their preferred
food, are common. Sasa Bay, which is located in the backwaters of Apra Harbor, appears to be
an area where hawksbills are most often encountered (Gutierrez 2004). Randall et al. (1975) note
that hawksbills have also been sighted in the protected waters of Cocos Lagoon. Hawksbill turtles
are also regular inhabitants of Tinian, albeit in much fewer numbers than green turtles. Even
though past surveys at Tinian (1984/1985, 1994/1995, and 2001) have failed to produce a single
sighting record, time and area constraints may have led to foraging hawksbills being missed
(Wiles et al. 1989; Pultz et al. 1999; Kolinski 2001). The only occurrence records that exist for
FDM are two in-water sightings at the southwestern corner of the island in 2001 and one at the
northwest corner of the island in 2004 (DoN 2005b). Each of these observations was recorded
during Navy-sponsored marine tow and SCUBA dive surveys around the island. Both of the
hawksbills sighted in 2001 were immature individuals less than 50 cm in carapace length, while
the individual observed in 2004 was somewhat larger at 70 cm in carapace length (DoN 2005b).
There are only a few documented records of hawksbills nesting in the Marianas region although
only a subset of the region’s beaches are adequately surveyed for sea turtle nesting activity. One
hawksbill nest was recorded between Urunao Point and Tarague Beach (northern Guam) in 1984
and single nesting events were recorded on a small beach at Sumay Cove, Apra Harbor in 1991
and 1992 (Davis n.d.; NMFS 1998). Hawksbill turtles have not been observed to nest on Tinian
although nesting attempts could be made at times and locations where surveys are not being
conducted. Since hawksbills prefer to nest in areas with sufficient vegetative cover, it’s possible
that some nests are never found on surveyed beaches. Lund (1985) notes that hawksbill nests
are often very difficult to identify when qualified observers are not present. Hawksbills are unlikely
to be encountered on the beaches of FDM, which are unsuitable for nesting (DoN 2003b).
Behavior and Life History—Early juveniles are believed to utilize pelagic Sargassum or other
flotsam as a developmental habitat, but little is known about their diets during this stage. Upon
recruiting to benthic feeding habitats, hawksbills are known to become omnivorous and will feed on
encrusting organisms such as sponges, tunicates, bryozoans, algae, mollusks, and a variety of other
items such as crustaceans and jellyfish (Bjorndal 1997). Older juveniles and adults are more
specialized and feed primarily on sponges. Sponges comprise as much as 95% of their diet in some
locations (Witzell 1983; Meylan 1988).
Hawksbill turtles often nest in multiple, small, scattered colonies. Nesting is often seasonal, but can
extend throughout the year with one or two peaks. In Palau, for example, hawksbill nesting is known
to occur year round with peaks from June to August and December to January. Since very few data
are available for hawksbills that nest in Micronesia, much of the information presented below is taken
from studies of other rookeries in the Caribbean, Indian Ocean, and western Pacific regions. Mating is
believed to take place in the shallow waters adjacent to the nesting beach. Nesting occurs on both
low- and high-energy beaches in tropical latitudes. It is often a nocturnal activity that occurs on
beaches with sufficient vegetative cover. Females will often nest between two and five times per
season with inter-nesting intervals of about 14 to 16 days. The typical remigration interval is two to
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