Between 30th July and 8th August 2006, six female green turtles (Chelonia mydas) were fitted with Kiwisat 101 satellite transmitter tags shortly after nesting on Rekawa beach on the south coast of Sri Lanka as part of the IOSEA Year of the Turtle celebrations. The tags were attached by staff from the Marine Conservation Society (MCS), the Turtle Conservation Project (TCP) Sri Lanka, Nature Friends of Rekawa (NFR) and the Department of Wildlife Conservation (DWC) Sri Lanka, with the help of several enthusiastic and capable TCP and UN volunteers.
The turtles were tracked online using Seaturtle.org's excellent Satellite Tracking and Analysis Tool (STAT)1 and the tags transmitted for between 61 and 169 days, with the last accurate transmission from the last remaining active tag received on the 23rd January 2007. Almost 70 years after the publication of Deranyagala's first observations of nesting marine turtles in Sri Lanka, the data generated by this project represents the first detailed insight into the inter-nesting behaviour, migration and foraging grounds of the female green turtles nesting on the island's shores2.
The first turtle to be tagged (Helen) immediately began her post-nesting migration after her release, but four of the other turtles appeared to consistently inter-nest in inshore waters adjacent to Rekawa beach. This suggests that these local waters, some of which lie within the recently designated Wildlife Sanctuary at Rekawa, provide key inter-nesting habitat for the female green turtles during the nesting season. After nesting at Rekawa, the other turtle (Vihara Mahadevi) inter-nested at Habaraduwa, an unprotected site approximately 70km west along Sri Lanka's coast, staying there for 4 weeks after her last nesting activity at Rekawa before her tag failed unexpectedly early. It is possible that the inshore habitat at Habaraduwa is the location of this turtle's residential feeding ground, or perhaps she was resting there in preparation for another nesting event or a longer migration away from Sri Lanka.
After completing their last nesting activities at Rekawa, the other five turtles migrated to three general areas, suggesting that, as with green turtle breeding populations elsewhere, the nesting females' resident foraging grounds are diverse and distant from Rekawa. Three turtles (Helen, Tharushi & Manike) migrated to separate foraging grounds in the Gulf of Mannar Biosphere Reserve (GoMBR) off the coast of Tamil Nadu, India, located over 400km (straight-line) north west of Rekawa. Another turtle (Kinduri) migrated to Minicoy, the most southerly of India's Lakshadweep Islands, some 927km (straight-line) north west of Rekawa. The turtle with the tag that sent the last accurate transmission (Sayuri-Emerald) migrated up the west coast of India to an area off Bhatkali, Karnataka, some 1,137km north west of Rekawa. While a sample of six turtles cannot be representative of the hundreds of green turtles that nest at Rekawa, these initial results suggest that India's territorial waters could provide key foraging habitat for a significant percentage of Sri Lanka's nesting green turtles.
The five turtles that migrated away from Sri Lanka appeared to use the coast of Sri Lanka as a navigational cue in the early stages of the migration. The turtles did not appear to be foraging during this stage of their migrations and were swimming approximately 45kms per day. However, they were swimming through heavily fished inshore waters and so ran the risk of accidental entanglement in nets and longlines set in the water column along their migration route3. In addition, the three turtles that migrated to the GoMBR crossed the heavily fished waters of the Gulf of Mannar, an area known to be a local hotspot for marine turtle bycatch and directed take4.
Little is known about turtle bycatch in the GoMBR, but available literature suggests that these turtles may not be exposed to the high levels of directed exploitation reported elsewhere along the Tamil Nadu coast, largely due to the State protection measures afforded within the Reserve5. The turtle that migrated to Minicoy may also be less likely to be exposed to directed take than elsewhere in the Lakshadweeps, at least from local fishers, as the Minicoy community is predominantly Muslim and relatively wealthy, and so historically not heavily dependent on a turtle harvest6, 7. The turtle that migrated to the coastal waters of Karnataka appeared to be resident in an area with some artisanal fishing, although little is known about marine turtle bycatch there8.
The provisional findings of this project reinforce previous TCP work and highlight the potential threat that Sri Lanka's nesting turtles face from the country's inshore fisheries. Furthermore, the findings suggest that both India and Sri Lanka have important roles to play in conserving the countries' shared and endangered green turtle populations. These roles could be reinforced via bilateral cooperation through regional agreements such as IOSEA.
MCS and the TCP hope to carry out further assessments of the environmental sustainability of selected Sri Lankan fisheries starting in 2007. In addition, MCS hopes to find further funding to attach satellite tags to more nesting green turtles at Rekawa in summer 2007 to improve the scientific integrity of this study. The data from all the tags will be analysed by Peter Richardson at the MCS and Drs Brendan Godley and Annette Broderick at the University of Exeter for publication co-authored by all project partners at a later date.
The 2006 tagging project was filmed by a BBC Natural History Unit crew and will feature in a documentary about the TCP's pioneering work to be broadcast in Summer 2007 as part of a BBC flagship series entitled Saving Planet Earth. If you would like to support the additional satellite tagging, which will also feature in the BBC Saving Planet Earth series, contact Peter Richardson, MCS Species Policy Officer at peter@mcsuk.org.
Acknowledgements: Many thanks for the invaluable time and support from various members of staff at the MCS, TCP, NFR, DWC, Seaturtle.org and the University of Exeter, as well as the TCP and UN volunteers, without whom this project would not have been possible. Many thanks also to the project sponsors, including Defra via the Indian Ocean and South East Asia (IOSEA) Sea Turtle Agreement Secretariat, the Deep Aquarium in Hull and Hurtigruten, and finally to Paul Appleby and the BBC NHU for lending their weight to the momentum.
References:
1 Coyne MS & Godley BJ (2005). Satellite Tracking and Analysis Tool (STAT): An Integrated System for Archiving, Analyzing and Mapping Animal Tracking Data. Marine Ecology Progress Series 301: 1-7.
2 Deranyagala P (1939). Tetrapod reptiles of Ceylon. Vol. 1. Colombo Mus. Nat. Hist. 412pp.
3 Kapurusinghe T & Cooray R (2002). Marine turtle by-catch in Sri Lanka. TCP Survey report for CMS, ISBN 955-8758-01-9.
4 Kapurusinghe T (2006). Status and conservation of marine turtles in Sri Lanka. In (eds) Shanker K & Choudhury BC. Marine turtles of the Indian Subcontinent. Universities Press (India) Private Ltd.
5 Bhupathy S & Saravanan S (2006). Marine turtles of Tamil Nadu. In (eds) Shanker K & Choudhury BC. Marine turtles of the Indian Subcontinent. Universities Press (India) Private Ltd.
6 Tripathy B, Shanker K & Choudhury BC (2006). Sea turtles and their habitats in the Lakshadweep Islands. In (eds) Shanker K & Choudhury BC. Marine turtles of the Indian Subcontinent. Universities Press (India) Private Ltd.
7 Bhaskar S (1978). Marine Turtles in India's Lakshadweep Islands. Marine Turtle Newsletter, 8:5.
8 Sharath BK (2006). Sea turtles along the Karnataka coast. In (eds) Shanker K & Choudhury BC. Marine turtles of the Indian Subcontinent. Universities Press (India) Private Ltd.
