Individual study: Post-release swimming behaviour and dispersal in head-started loggerhead turtles Caretta caretta released on the islands of CuraÃ§ao and Klein CuraÃ§ao, Netherlands Antilles
Nagelkerken I., Pors L.P.J.J. & Hoetjes P. (2003) Swimming behaviour and dispersal patterns of headstarted loggerhead turtles Caretta caretta. Aquatic Ecology, 37, 183-190
Swimming behaviour and dispersal patterns were studied in 'head-started' loggerhead turtles Caretta caretta (i.e. young turtles initially reared in captivity prior to release in an attempt to help them through the especially vulnerable hatchling period of their life) which were released on the islands of CuraÃ§ao and at Klein CuraÃ§ao (Netherlands Antilles) in the Caribbean.
In August 1993, a local nest of hatchling loggerheads was brought to the CuraÃ§ao Seaquarium. After captive rearing for 1-2.5 years, a total of 23 turtles were released between 1994 and 1996 on three beaches on CuraÃ§ao (Blauwbaai, Seaquarium and St. Michielbaai) and one beach on the nearby island of Klein CuraÃ§ao.
Given concerns of possible negative behavioural effects of head-starting of turtles, their short-term swimming behaviour and dispersal were assessed. Turtles were tagged and fitted with a small radio transmitter. Upon release, the turtles were placed on the beach 4-7 m from the waterline from where they made there way into the sea. They were then followed by boat with a Global Positioning Unit up to a distance of 6,125 m offshore.
Upon release, the turtles immediately crawled towards the sea. Once in the water they submerged and swam rapidly away (almost continuously about 30 cm under the water surface) from shore (typical hatchling-type behaviour). Almost all swam away from the shore more-or-less perpendicular to the coastline for at least 1 km, usually for 3-4 km. Only one turtle (released at Blauwbaai) really deviated from this pattern; at about 800 m offshore it orientated itself parallel to the coastline but appeared to eventually swim offshore. The turtles also dived, dive frequency and duration being comparable to that of similar-sized wild turtles.
This small study demonstrates that the head-started loggerheads swam and dispersed in a similar way to wild hatchlings; as they exhibited offshore directional movement this suggests that head-starting had not affected their (short-term) orientation abilities. It is unknown whether the head-starting had any long-lasting effects on their survival.
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