The Hawksbill Turtle (Eretmochelys imbricata)
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This is a portrait of Keoki, a Hawaiian hawksbill we've met at Honokowai. Hawaiian hawksbills, or 'ea, are extremely rare. 49K JPEG |
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This is a portrait of Keoki, a Hawaiian hawksbill we've met at Honokowai. Hawaiian hawksbills, or 'ea, are extremely rare. 49K JPEG |
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The following is based on information from the Recovery Plan for Hawksbill Turtles in the U.S. Carribean Sea, Atlantic Ocean, and Gulf of Mexico, National Marine Fisheries Service and U.S Fish and Wildlife Service, 1993. Obtained from the National Marine Fisheries Service, St. Petersburg, Florida, and used with their kind permission.
The hawksbill is listed as an endangered species by the International Union for the Conservation of Nature and Natural Resources. It is also listed as endangered throughout its range by the Endangered Species Act of 1973. An exhaustive review of the worldwide conservation status concluded that the hawksbill is suspected or known to be declining in 38 of 65 geopolitical units where information is available.
Severe declines were noted in the western Atlantic Ocean and the Caribbean region. It is sobering to consider that current nesting levels may be far lower than previously estimated. Despite protective legislation, international trade in hawksbill shells and subsistence use of meat and eggs continue unabated in many countries and pose a significant threat to the survival of the species in the region.
The most recent status review of the hawksbill in the United States recognized that numerous threats still exist despite a decade of protection.
The following combination of characteristics distinguishes the hawksbill from other marine turtles:
Additionally, on land the hawksbill has an alternating gait, unlike the leatherback and green sea turtles.
The carapace is heart-shaped in the youngest turtles and becomes more elongated as the turtle matures. The sides and rear portions of the carapace are sharply serrated in all but very old animals. The epidermal scutes that overlay the bones are the tortoiseshell so prized by commerce. (See bekko.)
The scutes are unusually thick, overlapping at the posterior in most animals. Carapacial scutes are often richly patterned with irregularly radiating streaks of brown and black on an amber background. The scutes of the plastron are usually clear yellow, with little or no dark pigmentation.
The head is elongate and tapers sharply to a point and the lower jaw is V-shaped. It clearly gives the animal a bird-like appearance.
The hawksbill is a small to medium sized turtle. Nesting females average about 87 centimeters in curved carapace length and can weigh to 80 kilograms in the Caribbean. The record weight of one animal was 127 kg and was reported by Archie Carr in 1952. Hatchlings in the United States Caribbean average about 42 millimeters in straight carapace length and range in weight from 13.5 to 19.5 grams. (1 gram is roughly what one Smartie weighs.)
Hawksbills use different habitats at different stages of their life cycle. It is widely believed that posthatchling hawksbills are pelagic and take shelter in weedlines around convergence zones. Sargassum and floating debris such as styrofoam, tar balls, and plastic bits (all common components of weedlines) are consistently found in the stomachs of youngsters that strand in Texas.
It is likely the weedlines in the Gulf of Mexico serve as a habitat for hawksbill that enter the US waters.
Hawksbills reenter coastal waters when they reach about 20-25 cm carapace length. Coral reefs are the resident foraging grounds for juveniles, subadults and adults. Hawksbills exist on the diet of sponges--commonly found on the solid substrate of reef systems. Ledges and caves of reef systems provide these turtles with shelter for resting during the day and night. Hawksbills can be found around rocky outcrops and high-energy shoals, which are optimum sites for sponge growth.
Hawksbills nest on low- and high-energy beaches in tropical oceans of the world, frequently sharing high energy beaches with green turtles. Hawksbills will nest on small pocket beaches and, because of their small body size and agility, can cross fringing reefs that limit access by other species. They exhibit a wide tolerance for nesting substrate type. Nests are typically placed under vegetation.
Sponges are the principal diet of hawksbills once they enter shallow coastal waters and begin feeding on the bottom. While diet studies have focused on the Caribbean, there is evidence that eating sponges is a worldwide feeding habit. A high degree of feeding selectivity is indicated by the consumption of a limited number of sponge species. Sponge predation by hawksbills may influence reef succession and diversity by freeing up space on the reef for settlement by benthic organisms. The hawksbill's highly specific diet and its dependence on filter-feeding, hard-bottom communities make it vulnerable to deteriorating conditions on coral reefs.
The 6 month nesting season of the hawksbill is longer than that of other sea turtles. Nesting occurs between July and October and courtship and mating begin somewhat earlier. Nesting in the Caribbean is principally nocturnal, although rare daytime nesting does occur.
Nesting behaviour follows a general sequence of that of other species of sea turtles: emergence from the sea, site selection, site clearing and pit construction, egg chamber construction, egg laying, filling in the egg chamber, disguising the nest site, and returning to sea. The entire process takes about 1 to 3 hours.
Hawksbills nest on average 4.5 times a season and intervals of about 14 days. Hawksbills have a strong site fidelity to specific nesting beach areas and are capable of returning to the same place season after season. Clutch size is correlated to female carapace length. In Florida and the US Caribbean, clutch size is about 140 eggs. Eggs are about 40 mm in diameter and take about 60 days to hatch. Sex determination is likely temperature-dependent as in other sea turtles and many reptiles, but data is limited.
Hawksbills face most of the same threats that endanger all marine turtles. Sadly, they are also singled out for their own special threat: humans find their shells highly attractive. The full extent of the threat is not known, but experts believe that the killing of hawksbills for bekko is a major problem.
Japan is the major consumer of bekko, but there is significant trade within the Caribbean as well. Although Japan has signed the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), it exempted itself from the ban on hawksbills (among others). Likewise, Cuba exempted itself, giving rise to a convenient trade opportunity.
Other countries, notably Indonesia, openly ignore their obligations under CITES and trade in hawksbills anyway. Finally, some countries with hawksbills, such as Haiti, do not belong to CITES.
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