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

Richard Grainger,Gabriel E Machovsky-Capuska,David Raubenheimer,Victor M Peddemors

doi:10.3389/fmars.2020.00422

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.

Highlights

Marine top predators shape their ecosystems through diet and nutrition (Machovsky-Capuska and Raubenheimer, 2020)
We have provided the first detailed description of the diet of juvenile white sharks in eastern Australia, revealing the importance of both benthic and pelagic prey resources, with evidence for possible sex-based dietary variation
A novel application in elasmobranch diet studies, enabled us to establish the macronutrient compositions of prey, diets and the nutritional niches in which white sharks forage, and how niche breadth may vary with shark size

Summary

Introduction

Marine top predators shape their ecosystems through diet and nutrition (Machovsky-Capuska and Raubenheimer, 2020). Despite their ecological importance, population declines and foragingassociated conflicts with humans are widespread among marine predators, posing significant management challenges (Heithaus et al, 2008; Guerra, 2019). White Shark Diet and Nutrition broader aspects of their ecology (e.g. movements, habitat use) which are relevant for addressing these management challenges, the diet of many top predators remains poorly characterised (Ramos and Gonzalez-Solis, 2012; Machovsky-Capuska et al, 2016a). Our understanding of the drivers of foraging in marine predators will remain limited if diets are described solely, on a taxonomic basis, as the combination of prey species that a predator consumes. A nutritionally explicit approach that distinguishes between multiple functional food components (nutrients) and links physiology, behaviour and ecology can enable a better understanding of animals’ responses to their environment (del Rio and Cork, 1997; Raubenheimer et al, 2009)

Methods

Results

Conclusion