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 ®shing trawls, but speci®c 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, ®sh made up the most important prey group, followed by pelagic tunicates, crustaceans, molluscs and other invertebrates. The importance of ®sh as a food resource has been rarely reported, and several lines of evidence indicated that ®sh were possibly consumed as discarded by-catch. This raises the question over whether or not western Mediterranean ®sheries are an important food source for juvenile loggerheads. The number and diversity of prey increased with turtle size, this may re¯ect 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.

Demographic implications of alternative foraging strategies in juvenile loggerhead turtles Caretta caretta of the North Pacific Ocean

“…However, pelagic red crabs occurred at lower frequencies and fish occurred at higher frequencies compared with previous studies with considerably smaller sample sizes (Ramirez-Cruz et al 1991. Loggerheads are opportunistic, generalist foragers and are known to consume fish as fisheries discards and directly from fishing gear (Shoop & Ruckdeschel 1982, Tomas et al 2001. The fish species retrieved from stomachs in this study were demersal predators of no commercial value that are frequently caught and discarded by local gillnetters (J. Lucero-Romero pers.…”

Site specialists, diet generalists? Isotopic variation, site fidelity, and foraging by loggerhead turtles in Shark Bay, Western Australia

“…longer-duration deployments, improved image quality, and a better camera angle) are required to make stronger inferences. Second, large body size might be expected to lead to an increasingly general diet, as larger turtles are able to feed on larger prey (Tomas et al 2001) but may continue to feed on small items, which was observed in the same turtle's AVED deployment. Increased prey diversity in larger turtles has been noted in loggerhead stomach contents (Tomas et al 2001, but see Limpus et al 2001, although this diversity could also reflect bias due to larger stomach (i.e.…”

“…Furthermore, intrapopulation variation in foraging behavior and diet is an important, unresolved issue (Vander Zanden et al 2010). While it is known, generally, that loggerheads consume diverse invertebrate taxa at the population level (reviews in Dodd 1988, Bjorndal 1997; see also Plotkin et al 1993, Casale et al 2008, Lazar et al 2011, relatively less is known about potential foraging variation within populations related to factors such as size, sex, regional influences, or individual specializations (but see , Tomas et al 2001, Hatase et al 2002, Hawkes et al 2006). Such information is necessary to improve our understanding of loggerheads' functional roles and evaluate the efficacy of management strategies (Hamann et al 2010).…”

Foraging ecology of loggerhead sea turtles Caretta caretta in the central Mediterranean Sea: evidence for a relaxed life history model

“…This is not a simple task, since loggerhead turtles in the neritic stage are known to feed throughthe whole water column (Bolten 2003), so that finding pelagic and benthic prey in the same sample (e.g. Tomas et al 2001) is not proof of a transitional stage.Small loggerhead turtles (minimum size: 29.5 and 22 cm respectively; Casale et al 2004aCasale et al , 2007a, have been caught by bottom trawlers in 2 of the few wide continental shelves of the Mediterranean basin, the north Adriatic and the central Mediterranean Sea, and an early recruitment to the north Adriatic neritic area was hypothesized (Casale et al 2005a, Lazar et al in press). On the other hand, loggerhead turtles caught by pelagic longliners have been assumed to be in the oceanic stage, in contrast to the assumption that those caught by bottom trawlers are in the neritic stage, and this has important implications for the interpretation of data and patterns in the Mediterranean Sea (e.g.…”