Differences in juvenile white sharks’ (Carcharodon carcharias) resource use in southern California waters

Context The white shark (Carcharodon carcharias) is a marine predator with a global distribution, ranging from neritic to oceanic waters. In the Southern California Bight (SCB), juvenile white sharks (JWS) form loose aggregations at nearshore habitats (<500 m from shoreline), but may also be encountered offshore (>5 km from shore) where they are vulnerable to interactions with recreational and commercial fisheries. Aim This study aimed to identify dietary differences, habitat preferences, and potential behavioral ecotypes among JWS encountered nearshore versus offshore, contributing to an understanding of their habitat use and associated vulnerabilities. Methods Tissue samples from sharks encountered nearshore and offshore (>5 km from shore) were taken for stable isotope analysis (SIA). Nearshore and offshore prey baselines were constructed using samples from potential prey species found at known nearshore JWS nursery habitats, and isotope values of offshore prey from the published literature. Sharks were also tagged with acoustic transmitters to track coastal movements Key results Both 13C and 15N values were significantly different between sharks encountered at different habitat types (nearshore vs offshore). Bayesian mixing models showed high dietary contribution from nearshore–coastal prey in sharks sampled nearshore, whereas those caught offshore exhibited higher contributions from pelagic–offshore food sources. A coastal residency index calculated for both shark groups during sampling years (2020–2022) showed that sharks caught offshore are detected less frequently in nearshore waters than are those tagged nearshore. Conclusion Juvenile white sharks in the SCB appear to form two distinct ecotypes. Implications These two groups of JWS may be exposed to different fisheries exposure depending on habitat use. A better understanding on JWS habitat and resource usage may help improve fisheries managements.