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Figure 1. Hawksbill foraging grounds in Brazil (this study): Arvoredo Marine Reserve, Abrolhos Marine Park and São Pedro e São Paulo (SPSP).

Snorkel and scuba dives were conducted for in-water observations and turtle captures. For each turtle sighting we recorded the date, time, dive location, depth, substrate type, estimated carapace length, behavior (swimming, feeding, resting on the bottom, assisted resting – turtle resting under any structure – and associations with fish) and other relevant characteristics (methods adapted from Houghton et al. 2003). We also attempted to photograph behavior and the facial profiles of each sea turtle. When possible, hawksbills were manually captured after recording the sighting. Captured turtles were tagged (Inconel tags provided by Project Tamar-ICMBio), weighed, measured (curved carapace length – CCL) and photo-identified (Reisser et al. 2008). Epidermis and scute samples were also taken for genetic and isotope analysis. After these procedures were complete, the turtles were immediately released close to their capture locations.

From a total of 80.1 dive hours performed at Abrolhos there were 162 underwater sightings and 65 individual hawksbills captured. At SPSP we dived for 29.2 hours and this resulted in 73 underwater sightings and 12 individuals captured. At Arvoredo Island we performed 235 dive hours with 22 underwater sightings and 6 individuals captured, and one of the turtles was subsequently recaptured twice.

Figure 2. Numbers of hawksbill turtles captured in Arvoredo Marine Reserve, Abrolhos Marine Park and São Pedro e São Paulo (SPSP), according to size classes.

The size of captured turtles ranged from 24.5 – 63.0 cm CCL at Abrolhos (mean = 37.9 cm), 30 – 75 cm at SPSP (mean = 53.7 cm), and 30 – 59.5 cm (mean = 41.3 cm) at Arvoredo (Fig. 2). Mean sizes were significantly larger at SPSP when compared to the other two areas (p < 0.05), but mean sizes between Abrolhos and Arvoredo did not differ significantly (p > 0.05), as demonstrated by a Student’s t-test. Due to the high abundance of small turtles at Abrolhos Park, we believe that this is an important recruitment area for hawksbill turtles. On the other hand, we observed relatively large size classes at SPSP and this indicates that this area is an important feeding ground for older hawksbills, perhaps due to its proximity to the Caribbean, where the majority of Atlantic hawksbill rookeries are located (Mortimer 2007).

Hawksbill feeding activity was recorded in 28.9% (n = 71) of the observations and consistently occurred at shallow portions of the reefs (depths shallower than 4 m) at Abrolhos and Arvoredo, and at greater depths (deeper than 8 m) at SPSP. Feeding occurred throughout the day (observed from 0600 to 1900 hours) and hawksbills seemed to select their prey by searching for them slowly while swimming close to the reef or rocks. In all of the feeding observations hawksbills selected sessile benthic organisms, mainly zoanthids (green sea mat, Zoanthus sociatus, and white encrusting zoanthid, Palythoa caribaeorum) and occasionally sponges. Although most studies on hawksbill diets report a preference for sponges (León & Bjorndal 2002; Meylan 1988), feeding on zoanthids has also been observed (Stampar et al. 2007).

Figure 3. Examples of hawksbill behaviors at the study sites: a/b) feeding on zoanthids; c) assisted resting; d) unassisted resting; e) Saint Paul’s gregory cleaning at SPSP; f) yellow line goby cleaning at Abrolhos. Red circles in e and f indicate fish locations. Images d and f are examples of typical underwater photo-id. Photographs by M.C.P.

Resting behavior (20.3% of sightings, n = 50) was also observed throughout the day, and hawksbills apparently chose deeper sites for this activity, resting mostly in spots deeper than 4 m at Abrolhos and Arvoredo, and greater than 10 m at SPSP. In 70% (n = 35) of resting observations turtles chose spots under rocks, demonstrating a preference towards assisted resting.

The frequency of other observed behaviors was found to be 48% (n = 118) swimming and 2.8% (n = 7) activity associated with reef fish. Cleaning activity on sea turtles by three reef fish species was recorded. There were four sighting at Abrolhos of cleaner fish (yellow line goby, Elacatinus figaro) nipping at the turtle’s carapace, with up to three fish cleaning simultaneously. There were two sightings at SPSP of the endemic Saint Paul’s gregory (Stegastes sanctipauli) cleaning the neck and carapace of a turtle and one observation at Arvoredo of a juvenile French angelfish (Pomacantus paru) feeding off a carapace. Associations between sea turtles and fish in Brazil have been recorded for many fish species including P. paru (Sazima et al. 2010), but to our knowledge this is the first record of E. figaro and S. sanctipaul cleaning hawksbill sea turtles.

By photographing the facial profiles of hawksbills upon initial capture, we were able to recognize some turtles (31 individuals on 52 occasions) through underwater photo-ID (see Figs. 3d and 3f). This demonstrates the great potential of photo-ID for conducting non-intrusive population studies. Intervals between initial capture and posterior “recaptures” (through underwater photo-ID or manual capture) varied from 1 to 242 days at SPSP, 1 to 297 days at Abrolhos, and 367 to 671 days for Arvoredo Island. We believe that additional field surveys would reveal even longer periods of permanency, further highlighting hawksbill residency at these feeding grounds. The permanency of this tropical species at

Arvoredo Island is remarkable considering that this area reaches temperatures as low as 13°C in the winter (pers. obs. in July 2007). This work demonstrates that Brazil hosts important hawksbill turtle foraging grounds, which should be preserved for the recovery of E. imbricata populations. Forthcoming stable isotope analyses will provide further understanding of hawksbill diet and habitat use at these Brazilian islands. Genetic studies currently underway will link these foraging populations to their stocks of origin, improving our current knowledge on hawksbill connectivity in the Atlantic Ocean and enhancing our ability to protect this species.

Acknowledgements. M.C.P. is a graduate student of the Programa de Pós-graduação em Oceanografia Biológica (FURG) and a scholarship recipient of the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES – Brazil). J.R. is sponsored by the International Postgraduate Research Scholarship (IPRS) and the CSIRO Flagship Collaboration Fund (Wealth from Oceans Flagship). E.R.S. is sponsored by CNPq (307843/2011-4). This project was made possible thanks to financial support from the Rufford Small Grants (RSG − UK) and field support from Abrolhos Park coordination and CECIRM PRO-Arquipélago. We acknowledge Projeto Tamar and ICMBio for their research partnership and permits. A special thank you to Berna Barbosa, Felipe Buloto and all the field assistants. This was a contribution from the Research Group ‘Ecologia e Conservação da Megafauna Marinha − EcoMega’.

HOUGHTON, J.D.R., M.J. CALLOW & G.C. HAYS. 2003. Habitat utilization by juvenile hawksbill turtles (Eretmochelys imbricata) around a shallow water coral reef. Journal of Natural History 37: 1269-1280.

LEÓN, Y.M. & K.A. BJORNDAL. 2002. Selective feeding in the hawksbill turtle, an important predator in coral reef ecosystems. Marine Ecology Progress Series 245: 249-258.

MEYLAN, A.B. 1988. Spongivory in hawksbill turtles: a diet of glass. Science 239: 393-395.

MORTIMER, J.A. 2007. The state of the world’s hawksbills. SWOT report – The State of the World’s Sea Turtles Vol. III, 44 pp.

MORTIMER, J.A. & M. DONNELLY. 2008. Hawksbill Turtle (Eretmochelys imbricata) Marine Turtle Specialist Group 2008 IUCN Red List status assessment. IUCN Red List of Threatened Species (<http://www.iucnredlist.org>)

REISSER, J., M. PROIETTI, P. KINAS & I. SAZIMA. 2008. Photographic identification of sea turtles: method description and validation, with an estimation of tag loss. Endangered Species Research 5: 73-82.

SAZIMA, C., A. GROSSMAN & I. SAZIMA. 2010. Turtle cleaners: reef fishes foraging on epibionts of sea turtles in the tropical Southwestern Atlantic, with a summary of this association type. Neotropical Ichthyology 8: 187-192.

STAMPAR, S.N., P.F. DA SILVA & O.J. LUIZ JR. 2007. Predation on the zoanthid Palythoa caribaeorum (Anthozoa, Cnidaria) by a hawksbill turtle (Eretmochelys imbricata) in southeastern Brazil. Marine Turtle Newsletter 117:3-5.