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MEPS prepress abstract   -  DOI:

Spatial distribution of sea turtles on South Atlantic subtropical reefs

Juliana Mello-Fonseca*, Cesar A. M. M. Cordeiro, Carlos E. L. Ferreira

*Corresponding author:

ABSTRACT: Environmental conditions have a strong influence on sea turtle population dynamics. Sea turtles spend most of their lives in foraging areas, however, there is a lack of information on how oceanographic and biological parameters determine habitat use and density. Here, we produce estimates of density for Chelonia mydas (green turtle) and Eretmochelys imbricata (hawksbill turtle) on a South Atlantic foraging area (Arraial do Cabo, Brazil). We also investigate the influence of environmental variables (wind fetch, temperature, depth, and visibility) and benthic composition on the distribution of turtles. Surveyed sites were split between a colder, more wave-exposed location (western), and a warmer, more sheltered location (eastern). To ensure that these mobile and sparsely distributed species were adequately surveyed, underwater visual censuses (timed transects) were conducted. Sea turtle densities were significantly different between warm/sheltered and cold/wave-exposed locations. C. mydas were almost 10 times more frequently sighted than E. imbricata. The local distribution of E. imbricata mirrored large-scale latitudinal patterns, where this tropical species is dominant on warmer reefs (similar to habitat conditions found in the eastern location). It was not possible to assess the environmental influence on E. imbricata sightings due to their low density. C. mydas were frequently sighted in the cold/exposed sites and negatively correlated with depth. Overall, the density of E. imbricata and C. mydas suggests that Arraial do Cabo is an important feeding ground in the western Atlantic Ocean. This study highlights that visual census can produce reliable density estimates of sea turtles in foraging areas.