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Sea turtle sightings were recorded opportunistically by 4-6 observers conducting visual cetacean census trips via boat along 30 km of the coast within our study site. The study area is characterized by shallow coastal bays outward to the seaward edge of the reef line, continuing to a distance of between 1 and 5 km (100 m depth), although some surveys extended as far as ~6 km from shore (1,000 m depth). Turtle sightings were recorded by Global Position System (GPS) and, where possible, water depth and species were noted and photographs taken.

Between April 2009 and December 2012, 116 sightings were recorded; both hawksbill and green turtles were observed but for the majority of sightings the species was unidentified. Sightings occurred throughout the study site and were generally restricted to depths of 50 m or less. Sightings within the Black River Bay limits comprised 35% of all sightings (not adjusted for effort) (Fig. 1).

Figure 1. Study area of the southwest coast of Mauritius Black dots indicate sightings of turtles between April 2009 - December 2012. The shaded area indicates land and the solid line indicates the external edge of the lagoon and reef complex.

In December 2009 an adult hawksbill was found floating in the lagoon at La Preneuse, however, upon examination there was no obvious cause of death. No additional mortalities were observed until 2012. During 2012, four turtle mortalities were recorded, all in the Black River Bay region where the boat sightings were concentrated. Boat strikes were suspected to be the cause of three green turtle mortalities due to carapace and flipper injuries (Table 1). The fourth, a hawksbill turtle, was found entangled in a discarded net but also displayed signs of fibropapillomatosis.

Table 1. Details of turtle mortalities in the Black River area between April 2009 and December 2012. Corresponding photos of turtles observed are shown in Fig. 2.

Figure 2. Photos of stranded turtles listed in Table 1.

The increase in turtle deaths in the area of Black River Bay raises concerns and questions about turtle occurrence, abundance, density and activities in the bay and how anthropogenic factors might be impacting them. The turtle deaths and our sightings results highlight the need for increased education and awareness about turtles in the area and we recommend the introduction of speed limits within the bay, which are currently lacking. Black River Bay is an important anchorage for the Mauritius west coast with numerous boats moving in and out of the bay, particularly during early morning and mid-afternoon when tour companies are operating excursions. In addition, the ongoing river marina development has the potential to alter current patterns, increase sedimentation, pollution (litter, noise) and boat traffic within potentially critical turtle habitat.

Marine turtle populations are under threat from numerous human activities that can cause direct (e.g., harvesting or bycatch), and indirect mortalities (e.g., habitat transformation or destruction, pollution) (Carr 1987; Shanker 2004; Troeng & Drews 2004). These are all relevant to Mauritius. As such, establishing site-specific sea turtle surveys to determine and monitor sea turtle population status is essential (Hamann et al. 2010; Wallace et al. 2010). In addition, it is important to record and describe turtle foraging sites to ensure the protection of key habitats and to determine the relationships between sea turtles and prey items and/or habitat (Rincon-Diaz et al. 2011).

While the number of turtle sightings could be interpreted as a positive sign that turtles are returning to use the coastal areas of Mauritius, steps need to be taken to ensure both turtle and habitat protection. The coastal zone of Mauritius is of critical importance to local subsistence, commercial and recreational activities with 70% of all tourists who visit the country participating in some sort of reef-based activities (Daby 2003; Ramessur 2004). In 2010 it was estimated this contributed US$ 697 million to the Mauritian economy (Mauritius Oceanographic Institute pers. comm. 2013). While environmental awareness in Mauritius has increased, this zone has been over-exploited and shows considerable environmental damage (Daby 2003; Fagoonee 1990), threatening the turtles that rely on it. In addition, reports of bycatch from local fishermen indicate that both green turtles and hawksbills are regularly caught in beach seines, bottomset gillnets and handlines and while the majority are released alive (69%), more than 20% were kept for food or medicinal use (Kiszka 2012).

Green turtle abundance is considered an indicator of the health and resilience of seagrass and reef ecosystems (Pandolfi et al. 2003). Hawksbill turtles also rely on coral reef and hard bottom habitats during juvenile and adult life stages (Meylan & Donnelly 1999). The results presented here suggest that Black River Bay is an important site for sea turtle aggregations. Further investigation into sea turtle relative abundance, distribution and habitat use within the bay is warranted. We hypothesize that the seagrass beds and reef habitats within our study site are critical habitats for foraging green and hawksbill turtles. In the near future, we hope to include satellite tagging to monitor turtle movement patterns around the island and within the Indian Ocean, to monitor possible nesting sites on the mainland and surrounding islets and to increase public knowledge and awareness as to the presence and importance of these animals, especially within Black River Bay. These efforts should run in parallel with reef and seagrass monitoring. Public awareness and education will allow us to engage our stakeholders and encourage them to advocate for effective sea turtle management and conservation.

Acknowledgements. We thank the volunteers of the Mauritius Marine Conservation Society for assistance in data collection and background research. Thanks to the staff of Dolswim for help with logistics and details of turtle deaths.

BOURJEA, J., R. NEL, N.S. JIDDAWI, M.S. KOONJUL & G. BIANCHI. 2008. Sea turtle bycatch in the WIO: Review, recommendations and research priorities. Western Indian Ocean Journal of Marine Science 7: 137-150.

CARR, A. 1987. Impacts of nondegradable marine debris on the ecology and survival outlook of sea turtles. Marine Pollution bulletin 18: 352-356.

CHAPMAN, R.E. & K.J. SWINNERTON. 1996. The Mauritius Wildlife Fund St. Brandon Expedition: Marine turtles. 7pp.

DABY, D. 2003. Effects of seagrass bed removal for tourism purposes in a Mauritian bay. Environmental Pollution 125: 313- 324.

FAGOONEE, I. 1990. Coastal marine ecosystems of Mauritius. Hydrobiologia 208: 55-62.

GRIFFITHS, O. & V. TATAYAH. 2007. Rapid survey of marine turtles in Agalega, Western Indian Ocean. Marine Turtle Newsletter 115:14-16.

HAMANN, M., M.H. GODFREY, J.A. SEMINOFF, K. ARTHUR, P.C.R. BARATA, K.A. BJORNDAL, A.B. BOLTEN, A.C. BRODERICK, L.M. CAMPBELL, C. CARRERAS, P. CASALE, M. CHALOUPKA, S.K.F. CHAN, M.S. COYNE, L.B. CROWDER, C.E. DIEZ, P.H. DUTTON, S.P. EPPERLY, N.N. FITZSIMMONS, A. FORMIA, M. GIRONDOT, G.C. HAYS, I.J. CHENG, Y. KASKA, R. LEWISON, J.A. MORTIMER, W.J. NICHOLS, R.D. REINA, K. SHANKER, J.R. SPOTILA, J. TOMAS, B.P. WALLACE, T.M. WORK, J. ZBINDEN& B.J. GODLEY. 2010. Global research priorities for sea turtles: informing management and conservation in the 21st century. Endangered Species Research 11: 245-269.

KISZKA, J. 2012. Bycatch assessment of vulnerable megafauna in coastal artisanal fisheries in the southwest Indian Ocean. Final Report to: South West Indian Ocean Fisheries Project. 113 pp.

MANGAR V. & R. CHAPMAN. 1996. The status of sea turtle conservation in Mauritius. In: HUMPHREY, S.L. & R.V. SALM (Eds.). Status of Sea Turtle Conservation in the Western Indian Ocean. IUCN/UNEP, Nairobi, Kenya.

MAURITIUS MARINE CONSERVATION SOCIETY (MMCS). 2002. Turtle Exploitation in Mauritius. Marine Turtle Newsletter 95:21.

MEYLAN A.B. & M. DONNELLY. 1999. Status justification for listing the hawksbill turtle (Eretmochelys imbricata) as Critically Endangered on the 1996 IUCN Red List of Threatened Species. Chelonian Conservation & Biology 3: 200-224.

PANDOLFI, J.M., R.H. BRADBURY, E. SALA, T.P. HUGHES, K.A. BJORNDAL, R.G. COOKE, D. MCARDLE, L. MCCLENACHAN, M.J. NEWMAN, G. PAREDES, R.R. WARNER & J.B. JACKSON. 2003. Global trajectories of the long-term decline of coral reef ecosystems. Science 301: 955-958.

RAMESSUR, R.T. 2004. Global environmental change affecting sustainable development of the coastal zone in Mauritius. University of Mauritius, Mauritius. <http://irfd.org/events/wfsids/virtual/papers/sids_rramessur.pdf>

RINCON-DIAZ, M.P., C.E. DIEZ, R.P. VAN DAM & A.M. SABAT. 2011. Foraging selectivity of the hawksbill sea turtle (Eretmochelys imbricata) in the Culebra Archipelago, Puerto Rico. Journal of Herpetology 45: 277-282.

SHANKER K. 2004. Marine turtle status and conservation in the Indian Ocean. FAO Fisheries Report No. 738 Supplement.

TROËNG, S & C. DREWS. 2004. Money Talks: Economic Aspects of Marine Turtle Use and Conservation. WWF-International, Gland, Switzerland. 64 pp.

WALLACE, B.P., A.D. DIMATTEO, B.J. HURLEY, E.M. FINKBEINER, A.B. BOLTEN, M.Y. CHALOUPKA, B.J. HUTCHINSON, F.A. ABREU-GROBOIS, D. AMOROCHO, K.A. BJORNDAL, J. BOURJEA, B.W. BOWEN, R.B. DUENAS, P. CASALE, B.C. CHOUDHURY, A. COSTA, P.H. DUTTON, A. FALLABRINO, A. GIRARD, M. GIRONDOT, M.H. GODFREY, M. HAMANN, M. LOPEZ-MENDILAHARSU, M.A. MARCOVALDI, J.A. MORTIMER, J.A. MUSICK, R. NEL, N.J. PILCHER, J.A. SEMINOFF, S. TROENG, B. WITHERINGTON & R.B. MAST. 2010. Regional management units for marine turtles: a novel framework for prioritizing conservation and research across multiple scales. PLoS ONE 5: e15465. doi:10.1371/journal.pone.0015465.