Abstract
Lipids are major sources of metabolic energy in sharks and are closely linked to environmental conditions and biological cycles, such as those related to diet, reproduction and migration. In this study, we report for the first time, the total lipid content, lipid class composition and fatty acid profiles of muscle and liver tissue of white sharks, Carcharodon carcharias, of various lengths (1.5–3.9 m), sampled at two geographically separate areas off southern and eastern Australia. Muscle tissue was low in total lipid content (<0.9% wet mass, wm) and was dominated by phospholipids (>90% of total lipid) and polyunsaturated fatty acids (34±12% of total fatty acids). In contrast, liver was high in total lipid which varied between 51–81% wm and was dominated by triacylglycerols (>93%) and monounsaturated fatty acids (36±12%). With knowledge of total lipid and dry tissue mass, we estimated the energy density of muscle (18.4±0.1 kJ g−1 dm) and liver (34.1±3.2 kJ g−1 dm), demonstrating that white sharks have very high energetic requirements. High among-individual variation in these biochemical parameters and related trophic markers were observed, but were not related to any one biological or environmental factor. Signature fatty acid profiles suggest that white sharks over the size range examined are generalist predators with fish, elasmobranchs and mammalian blubber all contributing to the diet. The ecological applications and physiological influences of lipids in white sharks are discussed along with recommendations for future research, including the use of non-lethal sampling to examine the nutritional condition, energetics and dietary relationships among and between individuals. Such knowledge is fundamental to better understand the implications of environmental perturbations on this iconic and threatened species.
Highlights
The white shark, Carcharodon carcharias, is considered the most voracious apex predator in temperate marine ecosystems worldwide [1], playing a key role in controlling ecosystem dynamics [2]
Lipid content and class composition White shark muscle was high in water (75.462.4%) and had a wet to dry mass ratio of 4.160.4 (Table 2)
Muscle was low in total lipid content and varied marginally between different body sections
Summary
The white shark, Carcharodon carcharias, is considered the most voracious apex predator in temperate marine ecosystems worldwide [1], playing a key role in controlling ecosystem dynamics [2]. Due to long standing declines in their population, white sharks are protected internationally; listed on Appendix II of the CITES and the Convention of Migratory Species [3] This makes assessing contemporary biological parameters difficult as investigative methods must be based on a limited number of samples, and be as non-invasive as possible. Much of our existing dietary knowledge on white sharks has been based on examining deceased sharks taken as incidental bycatch [4] or sharks taken as part of control programs [5] These data have been supplemented by in situ observations of predation at aggregation sites (typically around seal colonies) or scavenging events on whale carcasses [4,5,6,7,8] which, non-invasive, are likely to bias the recording of marine mammals in their diet. This has fueled a general (public) perception that white sharks almost exclusively consume prey comprising these taxa
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