Aerial survey abundance estimates of the loggerhead sea turtle Caretta caretta in the Pelagos Sanctuary, northwestern Mediterranean Sea

Abstract

Aerial line transect surveys, totalling 16 590 km, were performed in winter and sum- mer 2009 in the Pelagos Sanctuary, NW Mediterranean. A total of 207 loggerhead sea turtles were sighted, with only 9 sightings during the winter. In this season average raw 'surface' density (i.e. animals at or near the surface) was 0.002 turtles km -2 , and on the basis of line-transect analysis, we estimated 237 specimens (CV = 34.33%; 95% CI = 122-461). The summer estimate resulted in 4083 animals at surface (CV = 14.59%; 95% CI = 3061-5466) in the study area, with a density of 0.046 km -2 . Results indicated strong seasonal differences and lower densities than those found in comparable surveys in Spanish Mediterranean waters. Nevertheless, the ecological and oceano- graphic features of the Pelagos Sanctuary, established primarily for the protection of marine mam- mals, render it an important area also for Mediterranean loggerhead sea turtles. The potential for human-induced mortalities of turtles summering in the Pelagos Sanctuary is high. In this context, it is vital to obtain reliable estimates of absolute and relative abundance over time, monitor the sta- tus of loggerhead sea turtles and inform the development of effective conservation actions. This study illustrates the ability of aerial surveys to provide such data in this area.