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A similar pattern has often been observed with green turtles (Chelonia mydas). For example, aggregations of this species, which are usually associated with seagrass beds as their main feeding grounds, are also reported on coral reefs (Balazs 1979; Hirth 1992). As with green turtles, it is probable that hawksbill turtles frequently use habitats other than coral reefs for feeding and development. Here we report on the results of a preliminary in-water survey for marine turtles conducted on June 2003, along the southeast coast of the Dominican Republic, where we encountered a significant aggregation of juvenile hawksbill turtles in a shallow seagrass habitat.

Manglar Study Site is located at Saona Island on the southeast coast of the Dominican Republic (fig. 1). This site is characterized by seagrass beds protected by a reef breaker forming a lagoon, where water depth ranges from 0.5 to 2 meters. The dominant seagrass species are turtle grass (Thalassia testudinum) and manatee grass (Syringodium filiforme). Several species of algae (i.e. Halimeda incrasssata, Penicillus dumetosus and Udotea flabellum), and small colonies of corals (i.e. Monastrea sp.and Diploria sp.) were also found at scattered locations throughout the area (Vega et al. 1997, pers.obs.). The chicken-liver sponge (Chondrilla nucula) was also found encrusted among the turtle grass.

Figure 1. Map of surveyed area at Saona Island, Parque Nacional del Este, Dominican Republic.

Visual turtle surveys at the Manglar study site were conducted with four observers using a small boat and slowly navigating parallel to the shore. On some occasions we made attempts to catch sighted turtles. This was mostly accomplished by following a sighted animal until it tired and then by diving onto it from the bow of the boat (following Ehrhart & Ogren 1999). The survey transects start and end points, and turtle capture locations were recorded using a GPS receiver.

The relative sighting frequency (RSF) of sea turtles at the Manglar site was evaluated by dividing the number of turtles captured or sighted by the time spent surveying, with surveys typically lasting one hour for a total of three sessions. One session was conducted during morning hours and two sessions in the afternoon, for two days. The estimated size of all turtles was recorded together with species. All turtles handled were measured, weighed and marked on both front flippers with 681c style inconel tags. Individuals were also checked for the presence of internal passive integrated transponder (PIT) tags.

A total of 23 hawksbills and four green turtles were sighted during the boat surveys totaling three hours. Nine of the 27 turtles were captured. The resulting mean RSF for Manglar is 7.7 hawksbills per hour. The size range of the hawksbills captured was 29 to 41 cm curved carapace length (nuchal notch to posteriormost tip; CCLn-t; n=8), and sighted turtles were all estimated to be from 25 to 50 cm carapace length. Four green turtles were seen and one captured (measuring 33.3 cm CCLn-t). All green turtles observed were thought to be approximately 30 cm CCL.

Although our survey at Saona Island was far from complete, we note that a significant number of juvenile turtles are present, and specifically that hawksbill turtles inhabit this seagrass community. Whereas other reports of sporadic hawksbills residing in seagrass habitats exist, we believe the Manglar site is one of the first documented seagrass communities demonstrating a large abundance of hawksbill turtles. The high RSF of hawksbills recorded compares with study sites of important aggregations of this species. For example, a catch per unit effort of 3.4 and 4.7 hawksbills per hour have been recorded at Mona-Monito Island and Jaragua, Dominican Republic, respectively (Diez & Van Dam 2001; León & Diez 1999). We regard that this area is a developmental habitat, from the size range of turtles observed and captured in the area. Even though we did not conduct stomach content analyses, we speculate that these hawksbills are feeding on sponges such as chicken liver sponge (C. nucula), which is a common prey item for Caribbean juvenile hawksbills elsewhere (Andares & Uchida 1994; Leon & Bjorndal 2002; Meylan 1988; Van Dam & Diez 1997a).

In conclusion, juvenile hawksbill turtles living in habitats other than coral reefs may be more common than suspected. Further examination of other benthic communities for the presence of hawksbill turtles may widen the scope of characteristic habitats recognized for this species in the Caribbean. We caution that not only the most characteristic habitat type should be examined in any determination of the conservation status of sea turtle species.

Acknowledgements: To all the staff of Ecoparque, Inc. and the Comandancia de la Marina de Guerra de Bayahibe, Rep. Dominicana for the logistical and human support provided in the field. We would like to especially thank Kelvin Guerrero and our field assistants: Pedro Javier Santana, Félix Soto, Bienvenido, Chichi, El Negro Milady and El Toro. Also, we want to thanks Matilde Mota from the Ministerio del Medio Ambiente de la República Dominicana for arranging the research permit and Karen Bjorndal for kindly reviewing this manuscript. Project support came from Japan Bekko Association, Ecoparque Inc., Chelonia, Inc., and Departamento de Recursos Naturales y Ambientales de Puerto Rico.

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