Effects of short-term capture on the physiology of white sharks Carcharodon carcharias: amino acids and fatty acids

Abstract

Empirical evaluations of how overexploited marine fishes respond to capture stress (physiologically and behaviourally) have become increasingly important for informed fisheries management. These types of studies are, however, lacking for many protected species. Here, we conducted a novel study on the physiology of juvenile white sharks Carcharodon carcharias (139−325 cm fork length), a globally protected and ecologically important predator, in response to a standard fishery interaction using shark-management-alert-in-real-time (SMART) drumlines as part of a bather protection program. Specifically, we assessed the influence of short-term capture duration (average: ~30 min; range: 10−75 min) and other biological (size) and environmental (temperature) variables on blood plasma amino acids and fatty acids, which play essential roles as energy substrates as well as in maintaining physiological functions. None of the assessed amino acids or fatty acids were affected by capture duration, but some were influenced by shark size and water temperature. Our results support the notion that white shark physiology is robust to capture at short capture durations, which has important implications for the fate of released individuals.

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

“…There is consequently a clear need and growing public support for less invasive bather protection programmes that limit the potential for marine fauna to perish because of their use (Simmons & Mehmet, 2018). SMART drumlines have consistently resulted in few mortalities across multiple capture and tracking studies (Gallagher et al, 2019; Guyomard et al, 2019; Spaet et al, 2020a; Tate et al, 2019). The current study results support this, with only four deaths recorded, representing <1% of the total catch.…”

“…If a shark was caught on the line, it was only approached when it maintained a normal upright swimming position without heavy thrashing. The shark was then secured to the side of the vessel using a sling, with the vessel moving slowly to allow water to pass through the animal's gills (Gallagher et al, 2019; Tate et al, 2019). The sex and length (fork – FL to the nearest cm) of each animal were recorded, along with time (h: m) and location of capture and release.…”

“…The overarching aim of the NSW Shark Management Strategy is to increase protection for beachgoers by intercepting and catching white, bull and tiger sharks (hereafter referred to as target species) off coastal beaches, while minimising bycatch and mortality of all captured animals. To maximise the efficiency of the programme to deliver its objectives, trials were conducted in an experimental framework allowing tests of specific hypotheses (Gallagher et al, 2019; Tate et al, 2019). In the current study, various combinations of gear configuration and bait types, as well as the influence of environmental variables, were tested on white shark catches over a two‐year period.…”

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

“…Indeed, lipids are physiologically important to white sharks as an energy source for long-distance migrations and while inhabiting oligotrophic environments offshore (Del Raye et al, 2013). Gallagher et al (2019) identified increases in blood plasma FA associated with blubber consumption (Waugh et al, 2014;Meyer et al, 2019), and the utilisation of stored energy with size for juvenile white sharks in NSW. This further highlights the likely importance of body lipid stores for powering metabolism and movements in larger juvenile white sharks, even in coastal (less oligotrophic) settings (Gallagher et al, 2019).…”

The use of muscle lipids and fatty acids to assess shark diet and condition

“…Overall, this indicates that muscle FA profiles do not explicitly inform short‐ or long‐term activity levels (except for a few individual FAs) and instead remain usable indicators for abiotic and biotic ecology, including diet and habitat use (Beckmann et al ., 2013a; Meyer et al ., 2019a). As most FAs (9 of 10 for daily exercise and 8 of 10 for single‐day exercise) were not impacted by exercise (Table 3), it suggests their use in trophic ecology is not confounded by activities such as interacting with tourism operators (Meyer et al ., 2019b), capture stress (Gallagher et al ., 2019), or predator avoidance (Skomal & Bernal, 2010).…”