ONTOGENETIC CHANGES IN DIET AND HABITAT USE IN TIGER SHARKS (GALEOCERDO CUVIER) DETERMINED BY STABLE ISOTOPE ANALYSIS

Student: 
Alessia Scarpa
Room: 
room 1
session: 
Session 5, August 27, 09:00-10:30

Tiger sharks (Galeocerdo cuvier) are wide-ranging animals considered as top-order predators in marine ecosystems. The existing evidence suggests the occurrence of ontogenetic changes in habitat use and diet for the species however the understanding of this process is still limited. In this study we used stable isotopes of 13C and 15N of vertebrae to provide insights into potential ontogenetic shifts in trophic niche and habitat for this species in Australia. We also assessed the effect of sex and location on isotopic composition. We found that in utero stage had the largest niche, likely associated to the habitat use and diet of pregnant females that feed in a wider range of habitats. Differences between trophic niche of juveniles and adults were small but distinct when sexes were considered separately, suggesting that sex strongly influences changes in habitat use and diet of tiger sharks. Variations in isotopic composition were also influenced by location, indicating that local food-webs can determine the isotopic composition of tiger shark tissues. These results support shifts in resource and habitat use based on ontogeny but also sex and location. Our analysis also supports the use of stable isotope analysis as a tool to collect ecological information on wide-ranging species.