Elasmobranchs can detect minute electromagnetic fields, <1 nVcm–1, using their ampullae of Lorenzini. Behavioural responses to electric fields have been investigated in various species, sometimes with the aim to develop shark deterrents to improve human safety. The present study tested the effects of the Shark Shield Freedom7™ electric deterrent on (1) the behaviour of 18 white sharks (Carcharodon carcharias) near a static bait, and (2) the rates of attacks on a towed seal decoy. In the first experiment, 116 trials using a static bait were performed at the Neptune Islands, South Australia. The proportion of baits taken during static bait trials was not affected by the electric field. The electric field, however, increased the time it took them to consume the bait, the number of interactions per approach, and decreased the proportion of interactions within two metres of the field source. The effect of the electric field was not uniform across all sharks. In the second experiment, 189 tows using a seal decoy were conducted near Seal Island, South Africa. No breaches and only two surface interactions were observed during the tows when the electric field was activated, compared with 16 breaches and 27 surface interactions without the electric field. The present study suggests that the behavioural response of white sharks and the level of risk reduction resulting from the electric field is contextually specific, and depends on the motivational state of sharks.

The use of fatty acid (FA) tracers is a growing tool in trophic ecology, yet FA profiles are driven by a number of abiotic and biotic parameters, making interpretation and appropriate use confusing for ecologists. We undertook a global analysis, compiling FA profiles of 106 chondrichthyan (shark, ray and chimaera) populations, as a model to test the utility of FA profiles to partition a priori trophic guilds, phylogeny, water temperature and habitats. Individual FAs characterizing these four factors were identified, promoting the use of these FAs as ecological tracers across taxa. Habitat type was linked to five FAs: 16:0, 18:0 and biologically essential 22:6ω3 (indicative of the deep sea), 20:5ω3 (non‐complex demersal and deep‐sea demersal) and 20:4ω6 (reef and brackish water). Temperature was a key driver of four FAs (22:5ω6, 22:4ω6, 20:1ω9 and 20:5ω3), while trophic guild and phylogeny were important drivers of two pairs of FA tracers (18:0 and 20:5ω3; 20:1ω9 and 18:1ω9, respectively). This analysis provides a novel understanding of the biological and ecological information that can be inferred from FA profiles and further validates the use of FAs as tracers to investigate the trophic ecology of chondrichthyans. Future research should prioritize ex situ studies to further disentangle the influence of factors across taxa and tissue types, quantify biomodification, enabling the use of quantitative methods for diet determination and further develop ‘FATscapes’ to elucidate fine‐scale trophic geography and climate variability. Additionally, the creation of a taxonomically inclusive FA data repository will enable further meta‐analyses. A plain language summary is available for this article.

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Lipid and fatty acid (FA) analysis is commonly used to describe the trophic ecology of an increasing number of taxa. However, the applicability of these analyses is contingent upon the collection and storage of sufficient high quality tissue, the limitations of which are previously unexplored in elasmobranchs. Using samples from 110 white sharks, Carcharodon carcharias, collected throughout Australia, we investigated the importance of tissue type, sample quantity, and quality for reliable lipid class and FA analysis. We determined that muscle and sub-dermal tissue contain distinct lipid class and FA profiles, and were not directly comparable. Muscle samples as small as 12 mg dry weight (49 mg wet weight), provided reliable and consistent FA profiles, while sub-dermal tissue samples of 40 mg dry weight (186 mg wet weight) or greater were required to yield consistent profiles. This validates the suitability of minimally invasive sampling methods such as punch biopsies. The integrity of FA profiles in muscle was compromised after 24 h at ambient temperature (∼20 • C), making these degraded samples unreliable for accurate determination of dietary sources, yet sub-dermal tissue retained stable FA profiles under the same conditions, suggesting it may be a more robust tissue for trophic ecology work with potentially degraded samples. However, muscle samples archived for up to 16 years in −20 • C retain their FA profiles, highlighting that tissue from museum or private collections can yield valid insights into the trophic ecology of marine elasmobranchs.