Conservation ecology of coastal sharks and rays with a focus on the location and function of juvenile habitats

Marine protected areas (MPAs) are a key strategy for supporting the recovery of marine populations, in addition to the more general conservation of marine biodiversity. The effectiveness of this approach relies on the identification and protection of essential habitats and the processes that support habitat quality. The challenge here is to evaluate the importance of habitats in relation to their influence on population persistence, such as their role in promoting survival. For relatively mobile species such as coastal sharks, small-scale MPAs can be effective where key life stages are linked to predictable habitat features that are protected. Many sharks undergo changes in habitat requirements with increasing size that have implications for their vulnerability to anthropogenic impacts and the effectiveness of MPAs. In this thesis, I combine conservation biogeography and ecological approaches to assess the habitat requirements of coastal shark populations. In doing so, I quantified the habitat and foraging requirements of juvenile sharks at local scales, nested within a broader investigation of the habitat determinants of shark and ray distribution at regional (200–2,000 km) and continental (>2,000 km) spatial scales. My principal tools were baited remote underwater video stations (BRUVS), acoustic telemetry and stable isotope analysis. I found that latitude and depth can serve as surrogates of representative shark and ray assemblages for continental-scale conservation planning. Assessment of conservation planning at the regional-scale showed that high quality habitats for juvenile sharks were poorly represented in MPAs with the highest restrictions on fishing. I also found that salinity, temperature, turbidity, depth and distance to shore were important predictors of habitat suitability for juvenile sharks, but that preferences were species-specific. Movement models revealed that the youngest juveniles had high spatial and temporal overlap of distributions within inshore sandflat and fringing mangrove habitats in their natal environment. Small-scale MPAs (<20 km2) can therefore provide effective protection of these natal environments but the degree of protection will be sizeand species-specific. Finally, isotopic signatures of juvenile sharks indicate a dependency on coastal food webs and that diet overlap was likely mediated by intra-specific partitioning in δ15N niche space by specialist species and in δ13C space by generalist species. Vulnerability to resource fluctuations may be greater for specialist sharks rather than generalists. Establishing shark and habitat linkages enabled the evaluation of the effectiveness of MPAs for coastal shark populations at multiple scales and jurisdictions. Large-scale (>2,000 km) conservation planning to protect representative assemblages of coastal sharks and rays can benefit from bioregional habitat surrogates. However, strategic placement of large MPAs (200–2,000 km) to encompass the most suitable habitats for juvenile sharks will be enhanced by mapped predictions at the species-level rather than aggregate-level. Where speciesspecific information is missing or inadequate, no-take MPAs will likely need to be large to apply the precautionary principle and provide protection for mobile sharks. Smallscale MPAs (<20 km2) can be highly effective for species or life-stages with restricted movements and dependency on coastal food webs. Together, this multi-scale approach validates the importance of species-focused knowledge acquisition and management within this diverse predatory guild. In this context, the identification of key habitats and the processes that support habitat quality for sharks can inform spatial planning and complementary management efforts beyond MPA boundaries that are needed to fully protect exploited species.