engleski

Variability in movement patterns of immature Mediterranean loggerheads

Despite the recent progress in sea turtle life cycle understanding, thanks to satellite telemetry, the juvenile phases, namely the movements and the general at-sea behaviour of immature turtles, are still poorly studied. As for Mediterranean loggerheads, the available data on their distribution and movements are rather scarce and mainly based upon tag and by-catch analyses. Yet, recently satellite tracking has started to provide useful information in this respect. The purpose of this study was to investigate the at-sea behaviour of juvenile and sub-adult loggerheads by satellite tracking in various regions of the central Mediterranean sea, in order to compare the movement patterns displayed in different geographical areas and ecological conditions. The movement of sixteen late juvenile loggerheads (CCL between 47 and 87 cm) started to be monitored after their release, along three Italian marine zones, including the Northern Adriatic sea (including the Slovenian and Croatian side), the Northern Tyrrhenian sea and the Sicily Channel, around the Island of Lampedusa. All the turtles had been accidentally fished in the same region of release and recovered in different rescue centres. Those turtles were followed for periods of variable length (up to 451 days), during which they remained within the Central Mediterranean basin, most of them covering large distances, up to over 7500 km. The turtles, which had been tracked, displayed a number of different behavioural patterns as prolonged residence in fixed neritic locations, seasonal migrations towards southern regions, wandering circuitous movements over large neritic and oceanic areas, overwintering behaviour at high and low latitudes, with long-lasting dives. By combining location data with remotely-sensed oceanographic information, it has been possible to prove the main role of sea surface temperature (and, to a lesser extent, of chlorophyll concentration) in determining the kind and extent of turtle movements and behaviour. The reconstructed movements have confirmed the importance of the Gulf of Gabès and the North Adriatic sea as optimal foraging grounds for juvenile and sub-adult loggerheads in the Mediterranean Sea. Despite the fact that the North Adriatic sea is the coldest area in the Mediterranean, loggerheads may reside here also during the winter, although many tracked turtles did migrate southward as the cold season approached. According to these findings, other foraging areas have proved to be currently used by juveniles, such as the northern Tyrrhenian Sea, the Gulf of Naples or the Ionian Sea. In these cases, turtles mostly frequented the coastal shelf, that is the only neritic habitat available to them in these areas.

Satellite tracking; migration; fidelity; Caretta caretta; Mediterranean Sea

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