Methods

Seven female leatherback turtles were tagged with Kiwisat 202 Platform Transmitter Terminals (PTT), (Sirtrack Wildlife Tracking Solutions Ltd., New Zealand) at West Bay, Little Andaman. The transmitters interfaced with the CLS-ARGOS system for deriving surface position coordinates. The location coordinates were filtered and analysed using the Satellite Tracking and Analysis Tool (STAT) (Coyne and Godley, 2005). The PTTs were fitted with a salt-water switch which automatically switched on whenever the turtle surfaced to breath, sending location signals to the nearest geo-synchronised satellite in orbit. The PTTs were programmed with a duty -cycle to transmit continuously for the first three months, and every alternate day for the rest of the period. The PTTs were attached on the most prominent part of the medial carapacial ridge, usually posterior to the widest area of the carapace. Two holes were drilled through the medial ridge with an orthopaedic drill bit, with each hole only penetrating a few millimetres into the carapace. The transmitters were designed specifically for direct attachment to a leatherback turtle, and were secured on one side of the medial ridge using stainless steel cables inserted in surgical tubing, which acted as a sheath for the tether attachment. The cables were secured using stainless steel crimps. Direct attachment through the medial ridge has proven to be a successful alternative to the harness method (Fossette et al., 2008; Byrne et al., 2009). Using the described method, three nesting leatherback turtles were tagged during 2010- 2011 and four turtles were tagged during 2011-2012 nesting seasons.

Results

Of the seven turtles that were tagged, two turtles transmitted for about 6 months (179 and 193 days) and four turtles transmitted for 51 to 92 days; one turtle transmitted only a single data point (Table 1). Four out of six turtles travelled south east of the Andaman and Nicobar Islands, two along the coast of Sumatra, and two beyond Cocos (Keeling) Island towards Western Australia. Two turtles moved south-west of the islands, one of which travelled south of the British Ocean Territory (Figure 1). Turtle 103333, tagged on 04 January 2011, transmitted for 179 days and travelled the longest distance of 7312 km (straight line distance: 4185 km) (Table 1).

Three more turtles will be tagged with PTTs during the 2012-2013 nesting season.

Table 1. Post nesting migratory data of the leatherback turtles tagged in West Bay, Little Andaman.

Discussion

The patterns that emerged after satellite tracking of leatherback turtles from the Little Andaman Island provided some preliminary insight into their migratory patterns in the Indian Ocean. Upon departure from the West Bay Beach, leatherbacks migrated southward along varied paths, utilizing the broad expanses of the Southern Indian Ocean. While there was no single migratory corridor (Morreale et al., 1996; Benson et al., 2007), multiple turtles were observed to follow similar routes, with some relationship to bathymetry which requires further investigation. As the first telemetry study on leatherback turtles in the region, this provides useful information on their migratory pathways in the Indian Ocean, and highlights potential threats from deep sea fishing operations in the southern Indian Ocean. More data are, however, required to understand patterns of migration and identify specific threats during these migratory journeys.

Literature Cited

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