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Atlantic hawksbill sea turtle

Hawksbill sea turtles (Eretmochelys imbricatause) use different habitats at different stages of their life cycle [1]. Post-hatchling hawksbills occupy pelagic environments, taking shelter in weedlines that accumulate at convergence zones [1]. They reenter coastal waters when they reach approximately 20 to 25 cm carapace length [1]. Coral reefs are used as resident foraging habitat by juveniles, subadults and adults [1]. Along the eastern shores of continents where coral reefs are absent, hawksbills are known to inhabit mangrove-fringed bays and estuaries [1]. They feed primarily on sponges [1, 2]. Female hawksbills nest on low- and high-energy beaches of tropical oceans. Throughout their range, hawksbills typically nest at low densities with aggregations consisting of a few dozen, or at most a few hundred individuals [1]. Nests have been found on both insular and mainland beaches where nests are typically placed under vegetation [1]. Migratory patterns of hawksbills are not well known, although a reproductive migration is thought to take place [1,2].

Hawksbills occur in tropical and subtropical seas of the Atlantic, Pacific and Indian oceans and nest on beaches in at least 60 different nations [3]. Along the Eastern and Gulf coasts of the continental U.S., hawksbills have been reported by all of the Gulf states and from as far north as Massachusetts, although sightings north of Florida are rare [1]. Representatives of at least some life-history stages regularly occur in southern Florida (where the warm Gulf Stream current passes close to shore) and the northern Gulf of Mexico (especially Texas), in the Greater and Lesser Antilles, and along the Central American mainland south to Brazil [1].

The largest remaining concentrations of nesting hawksbills occur on the beaches of remote oceanic islands of Australia and the Indian Ocean [1]. The Yucatan peninsula in Mexico also supports a significant population of nesting hawksbills [1]. Within U.S. jurisdiction, nesting occurs principally on beaches in Puerto Rico and the U.S. Virgin Islands (USVI) [1]. The most important nesting sites are Mona Island (Puerto Rico) and Buck Island (St. Croix, USVI) [1]. Within the continental United States, nesting is restricted to the southeastern coast of Florida and the Florida Keys, where one or two nests have been reported annually [1].

Quantitative data on population changes of hawksbills are scarce, in part because hawksbills were already greatly reduced in number when scientific studies of sea turtles began in the late 1950s [3]. In addition, visual evidence of hawksbill nesting is the least obvious among the sea turtle species, because hawksbills often select remote pocket beaches with little exposed sand to leave traces of revealing crawl marks [1]. An estimate of the minimum number of female hawksbills in 1989 indicated that at least 15,000-25,000 female hawksbills nested annually worldwide [4]. Although global numbers are very difficult to estimate, it appears that this turtle has suffered drastic decline, probably by as much as 80% over the last century (3). Only five regional populations, Seychelles, Mexico, Indonesia, and two in Australia, support more than 1,000 nesting females annually [3]. Hawksbill populations are either known or suspected to be declining in 38 of the 65 geopolitical units for which nesting density estimates are available [3]

Hawksbill populations in the Western Atlantic-Caribbean region are thought to be greatly depleted [3]. In the Caribbean region, the number of females nesting annually is about 5,000 (order-of-magnitude estimate) [3]. With few exceptions, all of the countries in the Caribbean report fewer than 100 females nesting annually [3]. The largest known nesting concentrations are in the Yucatan Peninsula of Mexico [3]. These populations may be increasing [3]. A total of 4,522 nests were recorded in the states of Campeche, Yucatán and Quintana Roo in 1996, compared to only a few hundred in the early 1980s [5].

In the United States Caribbean, there is evidence that hawksbill nesting populations have been severely reduced during the 20th century [1]. At present, they are not believed to be declining, but neither are there clear signs of recovery, despite over a decade of protection [1, 3]. Estimates of the size of nesting populations under U.S. jurisdiction are available for only a few localities [1] and although trends are uncertain due to long intervals between hawksbill nesting generations (hawksbill take between 30 and 40 years to reach sexual maturity) and fluctuations in the number of reproductive females that nest in a particular year [3], hawksbill numbers seem to be increasing at two protected locations, Mona Island, Puerto Rico and at Buck Island Reef National Monument (BIRNM) in USVI [5]. The number of nests on Mona Island increased from 177 in 1974 to 537 in 1998 [5]. On BIRNM, the number of nesting females increased from 73 in 1987 to 121 in 1998 [5].

International commerce in hawksbill shell (“tortoiseshell” or “bekko”) may be the most significant factor endangering hawksbill populations worldwide [1]. Despite protective legislation, international trade in tortoiseshell and subsistence use of meat and eggs continues in many countries [1]. Females and eggs are vulnerable to poaching on nesting beaches and nests are vulnerable to beach erosion [1]. Egg poaching is a serious problem in Puerto Rico and also occurs in the USVI [1]. The practice of beach armoring can prevent females from reaching suitable nesting sites and can result in the loss of dry nesting beaches [1, 2]. Many hawksbill nesting beaches in the Caribbean are privately owned and in jeopardy of being developed [1]. Sand mining is also a threat to nesting beaches throughout the Caribbean [1]. The extent to which hawksbills are killed or debilitated after becoming entangled in marine debris has not been quantified, but it is believed to be a serious and growing problem [1]. Incidental catch in finfish fisheries may also pose a serious threat and the ingestion of marine debris (i.e. plastic bags, styrofoam) can result in hawksbill mortality [1].

[1] National Marine Fisheries Service and U.S. Fish and Wildlife Service. 1993. Recovery Plan for Hawksbill Turtles in the U.S. Caribbean Sea, Atlantic Ocean, and Gulf of Mexico. St. Petersburg, Florida.
[2] National Marine Fisheries Service and U.S. Fish and Wildlife Service. 1998. Recovery Plan for U.S. Pacific Populations of the Hawksbill Turtle (Eretmochelys imbricata). Silver Spring, MD.
[3] Meylan, A.B. and M. Donnelly. 1999. Status Justification for Listing the Hawksbill Turtle (Eretmochelys imbricata) as Critically Endangered on the 1996 IUCN Red List of Threatened Animals. Chelonian Conservation and Biology. 3(2):200–224.
[4] NatureServe. 2005. NatureServe’s Central Databases. Arlington, VA. U.S.
[5] Meylan. 1999. Status of the Hawksbill Turtle (Eretmochelys imbricata) in the Caribbean Region. Chelonian Conservation and Biology 3(2):177–184. Available at (http://www.iucn-mtsg.org/publications/cc&b_april1999/4.14-Meylan-Status.pdf).

Banner photo © Phillip Colla