Insights into the diet and trophic ecology of white sharks (Carcharodon carcharias) gained through DNA metabarcoding analyses of cloacal swabs

Abstract

AbstractThe 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.