Behavioural and trophic ecology of reef sharks at Ningaloo reef, Western Australia

Abstract

The focus of my project was to quantify the long-term movements, environmental associations, and trophic role of reef sharks at Ningaloo Reef, and relate findings to management. I reviewed 50 years of research on coastal shark movement and found common horizontal and vertical patterns, and relate these to habitat specificity, site fidelity, habitat partitioning and management. I monitored long-term (> 2 yrs) behaviour of four species of reef sharks (Carcharhinus melanopterus, Carcharhinus amblyrhynchos, Triaenodon obesus and Negaprion acutidens) at Ningaloo Reef using a combination of visual censuses, acoustic monitoring, and stable isotope techniques. All species showed site fidelity to inshore areas, one of which was an aggregation site (Skeleton Bay). Temporal and spatial overlap within Skeleton Bay was high for all species. Examination of environmental influences showed that sharks were more affected by water temperature than other variables, which suggests behavioural thermoregulation. Trophic level estimates were comparable to previous estimates based on dietary studies, and high δ13C suggests a dependency on coastal food webs. There was support for an increase of δ15N with body size, which suggests larger animals feed higher in the foodweb. Movement patterns around a sanctuary zone indicate that individuals were detected < 40 % of monitoring time. Adults had larger home ranges than juveniles, and activity hot spots for adults were outside of the sanctuary zone. Some Some adults made long-distance movements (> 10 km); the longest being 137 km. Management of reef sharks at Ningaloo should incorporate the use of MPA zoning with other measures such as migration corridors, and size and bag limits. Future research should adopt biotelemetry and molecular techniques, which would provide further detail on dispersal and interconnectivity of reef shark populations at Ningaloo and increase the resolution of habitat use and behaviour.