Sea turtle strandings along the Portuguese mainland coast: spatio-temporal occurrence and main threats

Abstract

The present study is a detailed analysis of sea turtle strandings over a 36-year period (1978–2013) along the Portuguese mainland coast. Out of the 806 stranded individuals, the loggerhead turtle Caretta caretta was the most frequent species (57.1 %) followed by the leatherback turtle Dermochelys coriacea (41.8 %), while green turtles Chelonia mydas and Kemp’s Ridley turtles Lepidochelys kempii were rare (respectively 1.0 and 0.1 %). Relative stranding densities of loggerheads showed an increase through time, whereas two leatherback stranding peaks were detected during the years 1994–1998 and 2009–2013. The highest loggerhead stranding density was observed on the southern coast during spring and summer when they are more susceptible to anthropogenic threats. The highest number of leatherback strandings was observed in the North-Central and Central-South western sectors during autumn and in the southern sector during summer, which may relate to seasonal food availability and water temperature considering those stranded animals that were subject to a post-mortem evaluation interaction with fisheries as the primary cause of stranding. Results show for the first time that waters off the Portuguese mainland coast is an important pathway for loggerheads and leatherbacks in the North Atlantic region. The present study serves as important baseline to the development of future sea turtle conservation efforts in the Portuguese mainland coast.