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Sea TurtlesHawksbill
Turtle
Hawksbill Turtle
Common Name: Hawksbill
Turtle
Scientific Name: Eretmochelys imbricata
Description
The hawksbill turtle is
small to medium-sized compared to other sea turtle
species. Adults weigh 100-150 lbs (45 to 68 kg) on
average, but can grow as large as 200 lbs (91 kg). Hatchlings
weigh about 0.5 oz (14 g).
The carapace (top shell)
of an adult ranges from 25 to 35 inches (63 to 90 cm) in length
and has a "tortoiseshell" coloring,
ranging from dark to golden brown, with streaks of orange,
red, and/or black. The shells of hatchlings are 1-2 inches
(about 42 mm) long and are mostly brown and somewhat heart-shaped.
The plastron (bottom shell) is clear yellow. The rear edge
of the carapace is almost always serrated, except in older
adults, and has overlapping "scutes".
The hawksbill turtle's head
is elongated and tapers to a point, with a beak-like mouth
that gives the species its name. The shape of the mouth allows
the hawksbill turtle to reach into holes and crevices of coral
reefs to find sponges, their primary food source
as adults, and other invertebrates. Hawksbill turtles are
unique among sea
turtles in that they have two pairs of prefrontal
scales on the top of the head and each of the flippers usually
has two claws.
Male hawksbills mature when they are about 27 inches (69
cm) long. Females mature at about 31 inches (78 cm). The ages
at which turtles reach these lengths are unknown.
Female hawksbills return to their natal beaches
every 2-3 years to nest at night approximately every 14-16
days during the nesting season. A female hawksbill generally
lays 3-5 nests per season, which contain an average of 130
eggs. Hawksbill turtles usually nest high
up on the beach under or in the beach/dune vegetation on both
calm and turbulent beaches. They commonly nest on pocket beaches,
with little or no sand.
Breeding areas and nesting seasons
Along the Great Barrier Reef,
hawksbills nest in low numbers from just north of Princess
Charlotte Bay to Torres Strait. Nesting also occurs in the
Northern Territory and Western Australia.
Two major breeding areas occur in Australia:
Northern Great Barrier Reef,
Torres Strait and northeastern Arnhem Land have several significant
rookeries including: Milman, Johnson, Bouydong, Bird and Piper
Islands in the northern GBR; Aukane, Kabikane, Mimi, Bet,
Sassie and Lacey Islands in Torres Strait; and Hawk, North
East and Truant Islands in north east Arnem Lan.
The north west shelf has several significant rookeries including Rosemary and Varanus Islands.
Although hawksbills breed
throughout the year, the peak nesting period in the Torres
Strait and Great Barrier Reef region occurs
between January and April. In Arnhem Land, nesting peaks between
July and September.
Diet
Sponges make up a major part of the diet
of hawksbills, although they also feed on
seagrasses, algae, soft corals and shellfish.
The hawksbill turtle has
a distinctive parrot-like beak.
Hawksbill turtle carapace:
4 pairs or more of large scales on either side (coastal scales)
Thick overlapping carapace scales
Carapace low domed with upturned edges
Colour olive grey
Adult carapace approx. 0.8m
Habitat
Hawksbill turtles use different
habitats at different stages of their life cycle, but are
most commonly associated with healthy coral reefs.
Post-hatchlings (oceanic stage juveniles) are believed to
occupy the "pelagic" environment, taking
shelter in floating algal mats and drift lines of flotsam
and jetsam in the Atlantic. In the Pacific, the pelagic habitat
of hawksbill juveniles is unknown. After a few years in the
pelagic zone, small juveniles recruit to coastal foraging
grounds; their size at recruitment is approximately 8-10 inches
(20-25 cm) in carapace length in the Atlantic and about 15
inches (38 cm) in carapace length in the Pacific. This shift
in habitat also involves a shift in feeding strategies, from
feeding primarily at the surface to feeding below the surface
primarily on animals associated with coral reef environments.
Here, juveniles begin feeding on a varied diet. In the Caribbean,
as hawksbills grow they begin exclusively
feeding on only a few types of sponges. However, in the Indo-Pacific,
hawksbills continue eating a varied diet that includes sponges,
other invertebrates, and algae.
The ledges and caves of coral reefs
provide shelter for resting hawksbills both during the day
and at night. Hawksbills are known to inhabit the same resting
spot night after night. Hawksbills are also found around rocky
outcrops and high energy shoals, which are also optimum sites
for sponge growth. They are also known to inhabit mangrove-fringed
bays and estuaries, particularly along the eastern shore of
continents where coral reefs are absent.
Population and Distribution
Hawksbills are solitary
nesters and, thus, determining population trends or estimates
on nesting beaches is difficult. The largest populations of
hawksbills are found in the Caribbean, the Republic of Seychelles,
Indonesia, and Australia.
The most significant nesting within the U.S.
occurs in Puerto Rico and the U.S. Virgin Islands, specifically
on Mona Island and Buck Island, respectively. Each year, about
500-1000 hawksbill nests are laid on Mona Island, Puerto Rico
(Diez and van Dam 2006) and another 100-150 nests on Buck
Island Reef National Monument off St. Croix in the U.S. Virgin
Islands (Z. Hillis-Starr. pers. comm.). Nesting also occurs
on other beaches in St. Croix and on St. John, St. Thomas,
Culebra Island, Vieques Island, and mainland Puerto Rico.
Within the continental U.S., nesting is restricted to the
southeast coast of Florida and the Florida Keys, but nesting
is rare in these areas. No nesting occurs on the west coast
of the U.S. mainland. In the U.S. Pacific, hawksbills nest
only on main island beaches in Hawaii, primarily along the
east coast of the island of Hawaii. Hawksbill nesting has
also been documented in American Samoa and Guam.
In addition to nesting beaches in the U.S.
Caribbean, hawksbills nest at numerous other
sites throughout the Caribbean, with the majority of nesting
occurring in Mexico and Cuba. In Mexico, about 2,800 hawksbills
nest in Campeche, Yucatán, and Quintana Roo each year
(Spotila 2004). Lutz et al. estimate the number of adult hawksbills
living in the Caribbean today is 27,000 (2003).
The largest nesting population of hawksbills
appears to occur in Australia. Approximately 2,000 hawksbills
nest on the northwest coast of Australia and about 6,000 to
8,000 off the Great Barrier Reef each year
(Spotila 2004). Additionally, about 2,000 hawksbills nest
each year in Indonesia and 1,000 in the Republic of Seychelles
(Spotila 2004).
Threats
Hawksbills face threats
on both nesting beaches and in the marine environment. The
primary global threat to hawksbills is habitat loss of coral
reef communities. Coral reefs are vulnerable
to destruction and degradation caused by human activities.
Humans can alter coral reefs either gradually (i.e., pollution
can degrade habitat quality) or catastrophically (e.g., toxic
spills and vessel groundings). Recent evidence suggests that
global climate change is negatively impacting coral
reefs by causing higher incidences of coral diseases,
which can ultimately kill entire coral reef communities. Hawksbill
turtles rely on coral reefs for food resources and habitat.
As these communities continue to decline in quantity and quality,
hawksbills will have reduced foraging opportunities and limited
habitat options.
Historically, commercial exploitation was
the primary cause of the decline of hawksbill sea turtles.
There remains a continuing demand for the hawksbill's shell
as well as other products, including leather, oil, perfume,
and cosmetics. The British Virgin Islands, Cayman Islands,
Cuba, Haiti, and the Turks and Caicos Islands (U.K.) all permit
some form of legal take of hawksbill turtles.
In the northern Caribbean, hawksbills are directly harvested
primarily for their carapace, which is often carved into hair
clips, combs, jewelry, and other trinkets. Additionally, hawksbills
are harvested for their eggs and meat while whole stuffed
turtles are sold as curios in the tourist trade. Hawksbill
products are openly available in the Dominican Republic and
Jamaica despite a prohibition on harvesting hawksbills and
eggs (Fleming 2001).
In the Pacific, directed harvest of nesting
females and eggs on the beach and hawksbills in the water
is still widespread. Directed take is a major threat to hawksbills
in American Samoa, Guam, the Republic of Palau, the Commonwealth
of the Northern Mariana Islands, the Federated States of Micronesia,
and the Republic of the Marshall Islands (NMFS and USFWS 1998).
In addition to directed harvest, increased human presence
is a threat to hawksbills throughout the Pacific. In particular,
increased recreational and commercial use of nesting beaches,
beach camping and fires, litter and other refuse, general
harassment of turtles, and loss of nesting habitat from human
activities negatively impact hawksbills.
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