Abundance and distribution of the endangered loggerhead turtle in Spanish Mediterranean waters and the conservation implications

GOMEZ DE SEGURA, A; TOMÁS, J.; PEDRAZA, S. N.; CRESPO, E. A.; ANTONIO RAGA, JUAN

ANIMAL CONSERVATION

Blackwell Publishing Ltd.

Lugar: Oxford; Año: 2006 vol. 9 p. 199 - 206

1367-9430

During two years (2001-2003) we performed seasonal aerial surveys in the central Spanish Mediterranean waters following the transect line methodology to determine the abundance and distribution patterns of loggerhead turtles (Caretta caretta). We surveyed a total of 16,700 km, amounting 770 turtle sightings. Loggerhead turtles were present in the area in high abundance, with densities varying from 0.051 to 0.430 turtles/km2. No differences were found between surveys, except in spring 2001, when density was higher than rest. Our results show that the Western Mediterranean is not a “summer” feeding area as previously proposed, but a high number of turtles are present all year around. Moreover, no clear migratory pattern was found; during the first year of study there probably was an entry of turtles in the study area in spring, but this pattern was not detected the next year. The average density of turtles in the whole study area was 0.21 turtles/km2 (95%CI: 0.17 - 0.25) and the mean abundance was 6,653 turtles (95%CI: 5,514 – 8,027). This result represents only the number of turtles at surface since a high proportion of turtles may be submerged while surveying, being undetected to observers. Correcting our estimations with recent diving behavior data, the absolute abundance would be 18,954 turtles (95%CI: 6,679 – 53,786). Having in mind that around 25,000 loggerhead are caught per year, our results indicate that the accidental captures seen to be an important threat for this species and conservation measures have to be implemented to avoid a non sustainable situation.