Diet Composition and Nutritional Niche Breadth Variability in Juvenile White Sharks (Carcharodon carcharias)

Abstract

Establishing diets and dietary generalism in marine top predators is critical for understanding their ecological roles and responses to environmental fluctuations. Nutrition plays a key mediatory role in species-environment interactions, yet descriptions of marine predators' diets are usually limited to the combinations of prey species consumed. Here we combined stomach contents analysis (n = 40), literature prey nutritional data and a multidimensional nutritional niche framework to establish the diet and niche breadths of white sharks (Carcharodon carcharias; mean ± SD precaudal length = 187.9 ± 46.4 cm, range = 123.8-369.0 cm) caught incidentally off New South Wales (NSW), Australia. Our nutritional framework also facilitated the incorporation of existing literature diet information for South African white sharks to further evaluate nutritional niches across populations and sizes. Although teleosts including pelagic eastern Australian salmon (Arripis trutta) were the predominant prey for juvenile white sharks in NSW, the diversity of benthic and reef-associated species and batoids suggests regular benthic foraging. Despite a small sample size (n = 18 and 19 males and females, respectively), there was evidence of increased batoid consumption by males relative to females, and a potential size-based increase in shark and mammal prey consumption, corroborating established ontogenetic increases in trophic level documented elsewhere for white sharks. Estimated nutritional intakes and niche breadths did not differ among sexes. Niche breadths were also similar between juvenile white sharks from Australia and South Africa. An increase in nutritional niche breadth with shark size was detected, associated with lipid consumption, which we suggest may relate to shifting nutritional goals linked with expanding migratory ranges.

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

“…They also estimated higher proportional contribution of inshore pelagic species to tissues of juvenile white sharks, and suggested that these prey were a more important dietary component than reported in previous studies (Santana-Morales et al, 2012;Malpica-Cruz et al, 2013). In contrast, we found a higher contribution from demersal prey to the isotopic composition of immature white sharks, consistent with the more benthic foraging previously reported (Tricas and McCosker, 1984;Hussey et al, 2012;Grainger et al, 2020). Their demersal prey species differed from those analyzed in our study.…”

“…Results from mixing models indicated that white shark muscle reflected demersal prey as the main contributor for all life stages. These results are similar to what has been reported for the diet of juvenile white sharks based on stomach contents analysis (Tricas and McCosker, 1984;Grainger et al, 2020), including samples from BSV where the most common items usually found are rays (mostly bat rays; Santana-Morales et al, 2012;pers. obs.).…”

“…Our results show that newborn shark muscle tissue was depleted in 13 C compared with the following life stages. Given that very young white sharks are known to feed on benthic prey (Tricas and McCosker, 1984;Grainger et al, 2020), these results suggest the prevalence of 13 Cdepleted maternal signature transferred to embryos during their gestation, as reported for other shark species with matrotrophic reproductive strategies (Estrada et al, 2006;McMeans et al, 2009;Olin et al, 2011Olin et al, , 2018. By the time sharks reached the YOY stage in our study, this maternal influence seems to have been diluted through the incorporation of new tissues during growth, leading to isotopic values similar to those of juveniles (Malpica-Cruz et al, 2013;Tamburin et al, 2020).…”

“…The white shark is a top predator that exhibits ontogenetic changes in its feeding habits and habitat use (Estrada et al, 2006;Carlisle et al, 2012;French et al, 2018). Whereas the feeding preferences of adults have been more widely studied (Estrada et al, 2006;Hussey et al, 2012), dietary information for the early life stages is more limited and suggest a more benthicoriented foraging (Santana-Morales et al, 2012;Grainger et al, 2020). Juveniles shift their diet from feeding on smaller bony fishes and elasmobranchs (mainly rays) to larger fishes as they grow.…”

The effectiveness of Shark‐Management‐Alert‐in‐Real‐Time (SMART) drumlines as a tool for catching white sharks, Carcharodon carcharias, off coastal New South Wales, Australia

“…White shark population estimates on the east coast of Australia suggest good survival rates of both juveniles (70%–75%) and adults (>90%) (Hillary et al, 2018). Juveniles undergo coastal migration (Bruce et al, 2019; Spaet et al, 2020a, 2020b), and their size and association with the coast place them in direct competition with other shark species that also hunt pelagic fish (Grainger et al, 2020). Evidence also suggests that white sharks are not only active hunters, but also opportunistic scavengers that often feed at slow speeds (Colefax et al, 2020; Tate et al, 2021).…”