The impact of wildlife tourism on the foraging ecology and nutritional condition of an apex predator

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

“…Lusseau and Derous (2019) allude to concerns about the preferential accumulation of FAs in different tissues, which may lead to tissue‐specific FA profiles in a predator differing substantially from the FA profiles of its' prey. Nonetheless, the use of muscle FA profiles to detail differences in predator foraging ecology, within either a species or taxonomically‐similar group, is well established for elasmobranchs ( e.g ., de Sousa Rangel et al ., 2019; Every et al ., 2017; Meyer et al ., 2019b in addition to the examples outlined in Meyer et al ., 2019a). The within‐species assessment in Meyer et al .…”

“…These biomarkers would likely complement the lipid metabolism approach used in Meyer et al . (2019b), and the present study recommends exploring their utility for studies of elasmobranch trophic ecology, physiology, and condition. The inclusion of ketone bodies and plasma markers was not feasible, as blood plasma could not be collected and the majority of the muscle samples were collected at a remote location from a cage on the ocean floor (Meyer et al ., 2018), preventing the samples from being immediately frozen or stored in liquid nitrogen.…”

“…Work highlighting the effects of repetitive disruptions on individuals, and subsequently populations, advocates for research to further the understanding of how nutritional condition is impacted by tourism (Gallagher & Huveneers, 2018; Pirotta et al ., 2018). The previous study in question used muscle lipids and fatty acids (FAs) to indicate a lack of detectable change in white shark Carcharodon carcharias L. 1758 diet and nutritional condition after interactions with the cage‐diving industry (Meyer et al ., 2019b). Nonetheless, Lusseau and Derous (2019) caution the use of muscle lipids and FAs to detail nutritional condition citing the unique energy metabolism of elasmobranchs, which relies more on ketone bodies than lipids for muscular energy (Speers‐Roesch & Treberg, 2010).…”

“…The use of muscle lipids and FAs to detail elasmobranch diet is well established (Beckmann et al ., 2014; McMeans et al ., 2012; Munroe et al ., 2018), with evidence of FA oxidation in muscle (Speers‐Roesch & Treberg, 2010) supporting the use of these biomarkers in Meyer et al . (2019b) to determine the dietary and nutritional impacts of cage‐diving on white sharks. Instead, Lusseau and Derous (2019) recommend the use of amino acids and ketone bodies in muscle tissue, and plasma markers of glutamate‐glutamine to investigate the impacts of disturbances on shark condition.…”

Eyes on the size: accuracy of visual length estimates of white sharks, Carcharodon carcharias

“…The white shark, Carcharodon carcharias , is a species for which visual length estimates are routinely used, including in assessments of residency and habitat use [30,31], fine-scale position and activity [32,33], population size and survival rates [34,35], and population dynamics and ontogenetic shifts [11,36–38]. Due to the difficulties of catching, restraining and measuring individuals, and the safety risks associated with handling large, potentially dangerous animals [8,39,40], visual estimation techniques are favoured over direct measurements.…”