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Movement and diving behaviour of late juvenile loggerhead sea turtles (Caretta caretta) in the western Indian Ocean

Year of publication 2013

Product type Meeting

Edition 1

Synopsis (short abstract) We conducted a satellite tracking study on juvenile loggerhead sea turtles in the Indian Ocean, where they have been poorly studied up to date. Eighteen individuals were released from Reunion Island (21.2°S, 55.3°E) to investigate movement and diving patterns of late juvenile stage in the region. Eleven turtles roughly swam towards Oman (20.5°N, 58.8°E), where one of the world largest rookery of loggerheads is located. Three individuals contrastingly went southwards off the coast South-Africa an d Madagascar, countries that also host loggerhead nesting grounds. Fourteen transmitters allowed the processing of animal diving profile and we observed a dichotomy between diurl and nocturl diving behavior with a greater number of shorter dives occurring during the day. Diving behavior also differed according to movement behavior as individuals spent more time at subsurface (<10m) during transit phases. Our study provides a better understanding of the oceanic movements and diving behavior of ju venile loggerheads, and key information for conservation of this species, which is of major concern in the Indian Ocean and worldwide.

Statutory body / Meeting title Indian Ocean Tuna Commission (IOTC)

Meeting symbol IOTC-2013-WPEB09-26

Meeting Session Number 9

Language English

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    Post nesting migration of green turtle (Chelonia mydas) in the western Indian Ocean 2013
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    Marine turtles do not recognize political boundaries, nor do they have regard for Exclusive Economic Zones (EEZ s), cooperative agreements, intertiol conventions, or memoranda of understanding between countries. So is it in the Southwest Indian Ocean (SWIO), a region that hosts some of the most important green turtle nesting sites in the world, most of which are isolated on remote islands (e.g. Europa and Glorieuses, Aldabra and Cosmoledo, Moheli and Mayotte). This region of the world is known t o have year round nesting of green turtles but all sites display a marked nesting season. However, very little is known about migratory pathways that sea turtles ply between their nesting and feeding grounds in this region where this species faces numerous threats such as fisheries interaction at both open sea and coastal waters. From 2009 to 2011, we deployed 81 satellite transmitters on nesting green turtle females during (d) and opposite (o) to the nesting peak in 5 important rookeries of the South West Indian Ocean (SWIO): Europa (Nd=10; No=10), Glorieuses (Nd= 10; No=10), Tromelin (Nd= 10; No=10), Mayotte (Nd=10; No=10) and Mohéli (Nd=7; No=3) and collected previous 24 old tracks in the area for a total of 105 tracks. First results showed that 39.7% of the tracked turtles used Madagascar costal foraging ground while more than 50% used the east African ones (Mozambique (32,0%), Kenya (3.8%), Tanzania (15,4%) and Somalia (2,5%)). It is worthwhile noting that the North Mozambique and South Tanzania remain the most important foraging ground for the tracked turtle (45% of the tracked turtles), but that they are mainly used by turtles tagged during the nesting season. On the other hand, we highlight here that green turtles also use a large range of foraging ground in the area (55% of the tagged turtles), some of them being hot spots (e.g. south of Maputo – Mozambique, Tulear lagoon – Madagascar). Spatial distribution estimation allowed identifying important year round coastal and oceanic migrating corridors: 2 oceanic corridors, (1) in the north of the Mozambique Channel (11°S - 14°S) and (2) the south of the Mozambique Chanel (17°S - 23°S), more particularly from the north of Europa to the north of Mozambique (38°E - 41°E); and 2 coastal corridors (1) The east African coast, between 16°S (Mozambique) and 7°S (Tanzania), and (2) all the west coast of Madagascar. The extreme north of Madagascar is also an important coastal migratory corridor The 105 tracked green turt les also crossed as many as nine different EEZs in the region before reaching their foraging grounds, which themselves are shared by six countries. Such spatial migrating pattern of adult green turtle, the temporal corridors and the regiol feeding hot spots identified are of high importance to implement targeted mitigating measures for artisal and industrial fisheries and encourage conservation on key foraging grounds.
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