Using gut contents to assess foraging patterns of juvenile green turtles Chelonia mydas in the Paranagua Estuary, Brazil

摘要

This study investigated use of the Paranaguá Estuary as a foraging habitat by juvenile green turtles Chelonia mydas (L.) by comparing gut contents to available vegetal resources within the estuary. Between June 2004 and July 2007, the carcasses of 80 juvenile green turtles (carapace length range 29 to 73 cm) were found stranded (n = 71) or captured (n = 9) in fishing nets. The digestive tracts of 76 turtles contained food contents which were quantified (ml) and identified (e.g. algae, seagrass, mangrove propagules, mangrove vegetation and shells). Anthropogenic debris was classified by material, colour and size. Green turtles fed primarily on Halodule wrightii (42.9% of total volume), other vegetal resources (Ulva spp.: 6.7%; Avicennia shaueriana propagules: 10.1%) and other items (37.9%); ingested animal matter was seldom recorded (2.4%). The occurrence and/or availability of vegetal resources were assessed throughout the year. H. wrightii was ingested more frequently during the early rainy season, when the index of importance in the diet was higher (feeding index, FI: 97.3). Ulva spp. was ingested principally in the late dry season and A. shaueriana propagules in the late rainy season (FI: 23.9 and 12, respectively), when H. wrightii was not available. Anthropogenic debris was frequently ingested (69.7% of individuals), and was especially important in the late rainy season (FI: 60.3). This study highlights the importance of sheltered ecosystems such as the Paranagua Estuary and adjacent regions in providing shelter, feeding grounds and resting areas for juvenile green turtles.