Feeding ecology of the loggerhead turtle Caretta caretta in the western Mediterranean

Abstract

We studied the feeding ecology of juvenile loggerhead turtles Caretta caretta in the western Mediterranean based on the contents of the digestive tract of 54 turtles (range of CCL: 34–69 cm) seized in Barcelona (Spain) in 1991. Turtles had been captured in fishing trawls, but specific information about dates and localities is not available. Despite this limitation, we obtained interesting evidences about the foraging strategies of loggerheads, with potentially important conservation implications. We report 33 new taxa in the diet. Results indicated that western Mediterranean loggerheads feed in an opportunistic way. Numerically, fish made up the most important prey group, followed by pelagic tunicates, crustaceans, molluscs and other invertebrates. The importance of fish as a food resource has been rarely reported, and several lines of evidence indicated that fish were possibly consumed as discarded by-catch. This raises the question over whether or not western Mediterranean fisheries are an important food source for juvenile loggerheads. The number and diversity of prey increased with turtle size, this may reflect the lack of prey selectivity of juvenile loggerheads coupled with a higher retention of food remains in larger turtles. Discounting prey that could be consumed as discarded by-catch, dietary data suggest that most, if not all, loggerheads of our sample were captured in neritic habitats. However, many turtles contained remains of both pelagic and benthic-demersal prey. These observations support the existence of an intermediate neritic phase in loggerheads' developmental shift from pelagic–oceanic to benthic–neritic foraging habitats, as previously suggested. During this phase, loggerheads would feed upon both pelagic and benthic prey.