Zach S. R. Clark

Bather protection programmes rely heavily on surveillance tools capable of detecting the presence of shark species that are known to physically interact with humans. This study investigates the potential for environmental DNA (eDNA) technologies to improve shark detection capabilities and complement current survey methods. We conducted a 14-month monitoring programme at two white shark (Carcharodon carcharias) visitation hotspots in eastern Australia and assessed spatio-temporal patterns of near-shore visitation using a species-specific eDNA assay, SMART (Shark-Management-Alert-in-Real-Time) drumline captures, and acoustic telemetry data from tagged white sharks. We observed higher shark detection frequencies across both survey locations using eDNA compared to the SMART drumline and telemetry survey methods. Specifically, eDNA surveys provided relatively constant rates of detection across the survey period, whereas SMART drumline and telemetry detections were highly seasonal and largely restricted to the austral winter–spring period. Findings from the eDNA surveys are consistent with current assumptions about white shark spatial ecology with year-long presence of white sharks in near-shore subtropical habitats in eastern Australia but suggest that shark presence during the summer–autumn months is possibly more prevalent than currently assumed. Overall, this study highlights the value of eDNA as a tool for enhancing shark detection capabilities, and the importance of adopting multiple complementary survey methods when assessing shark visitation rates. We discuss the implications of these findings for bather protection and white shark mitigation programmes in Australia and overseas.

Killer whales (Orcinus orca) have been documented to prey on white sharks (Carcharodon carcharias), in some cases causing localised shark displacement and triggering ecological cascades. Notably, a series of such predation events have been reported from South Africa over the last decade, with killer whales specifically targeting sharks' liver. However, observations of these interactions are rare, and knowledge of their frequency across the world's oceans remains limited. In October 2023, a 4.7 m (total length) white shark carcass washed ashore in southeastern Australia, coinciding with reports from citizen scientists of killer whales hunting a large, unidentified prey item in the area. Visual inspection of the carcass revealed that the liver, digestive, and reproductive organs were missing, and the presence of four distinctive bite wounds, one of which was characteristic of killer whale liver extraction as seen in South Africa. Genomic analyses performed on swabs taken from the bite wounds confirmed the presence of killer whale DNA in the major bite area, while the other bites were embedded with genetic material from the scavenging broadnose sevengill shark (Notorynchus cepedianus). These results provide confirmed evidence of killer whale predation on white sharks in Australia and the likely selective consumption of the liver, suggesting predations of this nature are more globally prevalent than currently assumed.

Wildlife surveys are central to the conservation and restoration management of wetland habitats; however, the often laborious and costly nature of traditional survey methods can constrain the spatial and temporal extent and replication of survey efforts. Environmental DNA (eDNA) technologies now provide the opportunity to reduce some of these limitations, but applications in temporary and permanent freshwater marshes and meadows (herein referred to as ‘wetland habitats’) remain limited. This study investigates the performance of single‐time‐point eDNA surveys for characterizing fish, amphibian and bird assemblages of wetland habitats in south‐eastern Australia. Comparisons were made between coastal and inland wetlands, between wetlands of varying condition and between eDNA and traditional surveys. Findings show that eDNA surveys can provide comprehensive descriptions of faunal assemblages associated with wetland habitats, with resolution similar to that provided by traditional survey approaches. Analyses also revealed significant differences in patterns of biodiversity between wetland types (coastal vs. inland) but not between wetland habitats varying in condition. Overall, this study confirms that eDNA surveys provide a reliable option for undertaking wetland biodiversity assessments aimed at improving biodiversity data coverage for otherwise data deficient wetlands.

The white shark (Carcharodon carcharias) is one of the world's largest apex predators found throughout the world's temperate and subtropical marine environments. However, the species has suffered significant declines in recent decades and effective conservation programs require a sound knowledge of white shark biology and ecology. In particular, information on white shark diet across life stages and the species' range is needed to identify critical trophic interactions supporting shark populations and to predict the resilience of white sharks to environmental changes. In this study, we reassess the diet and trophic ecology of white sharks via the genetic analyses of cloacal swabs from 214 juvenile and subadult sharks from eastern Australia. Our findings are largely consistent with those of previous studies based on visual analyses of gut contents but highlight the unprecedented taxonomic resolution of prey items offered by genomic assessments of shark cloacal swabs. Diets consisted primarily of ray‐finned fishes, with Mugiliformes, Carangiformes, Perciformes, and Scombriformes being dominant prey taxa, but with elasmobranchs, marine mammals, and birds also being common dietary constituents. Statistical analyses revealed a significant effect of sex and sampling location on diet composition, indicating biological and spatial variability in diets and predatory behavior. Overall, these findings support the notion that juvenile and subadult white sharks are opportunistic predators, which may provide some level of resilience to shifts in marine resources. However, frequently consumed ray‐finned fishes, many of which are commercially targeted, may be key to supporting white shark populations in eastern Australia. This study represents the most comprehensive analysis of juvenile and subadult white shark diets performed to date and provides added confidence in the genomic analysis of cloacal swabs for dietary assessments of predatory species. These results are expected to help inform management geared toward conserving this important marine predator across the world's oceans.