Interannual Nearshore Habitat Use of Young of the Year White Sharks Off Southern California

Abstract

Young-of-the-year (YOY) and juvenile-stage white sharks may use southern California nearshore beach habitats more extensively than previously known, within meters of some of the most heavily used beaches in the world. Such knowledge forms a critical component of species management and conservation plans, in addition to public safety and risk mitigation planning. We used data derived from a combination of satellite tag locations (13 animals over 3 years) and passive acoustic monitoring (34 animals over 8 years) to examine the occurrence, relative abundance, and residency patterns of YOY white sharks in southern California waters. Our results suggest that southern California contains spatiotemporally dynamic centers of primary nursery habitat. Tagged YOY white sharks formed loose aggregations at “hotspot” locations that were interannually variable, where individuals exhibited temporal fidelity, higher levels of residency, and spatially restricted movements, with multiple YOY individuals simultaneously displaying this behavior. While models of biotic and abiotic variables suggested relative abundance of tagged sharks may be predicted by sea surface temperature, salinity and productivity (chlorophyll-A), these predictors were not consistent across all years of the study. Thus, novel approaches that incorporate technologies to derive high resolution environmental data, paired with more comprehensive telemetry datasets are therefore required to better understand the extrinsic factors that drive habitat selection and residency patterns in juvenile white sharks.

Stable Isotope Analysis of Juvenile White Sharks Inside a Nursery Area Reveals Foraging in Demersal-Inshore Habitats and Trophic Overlap With Sympatric Sharks

“…Immature white sharks are known to primarily use coastal habitats, sometimes covering long distances (hundreds of kilometers) between nurseries (Dewar et al, 2004;Harasti et al, 2017;Curtis et al, 2018;Bruce et al, 2019;Anderson et al, 2021). We did not find significant differences in the mean δ 13 C or δ 15 N between juvenile sharks caught inside and outside BSV.…”

Non-random Co-occurrence of Juvenile White Sharks (Carcharodon carcharias) at Seasonal Aggregation Sites in Southern California

“…Although 10% of tagged sharks were identified at the same locations across more than 1 year, there was no evidence of stability in structure across multiple years, as returning sharks did not form repeated associations at monitored locations in subsequent years. Juvenile white sharks aggregating at nearshore locations, including those in this study, have been demonstrated to exhibit overlapping, restricted area use (Lyons et al, 2013;Anderson et al, 2021a). An individual's tendency toward association may be indicated by the propensity for spatiotemporal overlap and successive return to the same locations (Klimley and Holloway, 1999;Lilly et al, 2020), a trait exhibited in juvenile white sharks (Bruce et al, 2019;Spaet J. L. Y. et al, 2020;Anderson et al, 2021a).…”

“…Juvenile white sharks in southern California are known to seasonally aggregate in annually variable, spatially discrete nearshore locations (Lyons et al, 2013;White et al, 2019;Anderson et al, 2021a). The drivers behind these aggregation "hot spot" patterns, and the selection of specific habitat locations over an abundance of comparable available habitat remain unclear, and are not consistently explained by environmental correlates Anderson et al, 2021a).…”

“…Juvenile white sharks in southern California are known to seasonally aggregate in annually variable, spatially discrete nearshore locations (Lyons et al, 2013;White et al, 2019;Anderson et al, 2021a). The drivers behind these aggregation "hot spot" patterns, and the selection of specific habitat locations over an abundance of comparable available habitat remain unclear, and are not consistently explained by environmental correlates Anderson et al, 2021a). While the study included detection data from tagged juvenile white sharks at locations across southern California, a majority of annual detections and co-occurrences of tagged sharks occurred at seasonal aggregation hot spots, as indicated in Figures 2, 4.…”

“…These associations were also most prevalent in regions where resources were clustered (Jones et al, 2020). Southern California juvenile white shark aggregation hot spots have been largely associated with shallow, sandy beach habitat, although across southern California, such habitat constitutes < 30% of total available shore type (Anderson et al, 2021a). Although we were not able to quantify resource homogeneity at aggregation hot spots, hot spot locations themselves were annually spatially variable.…”