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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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