Diel Rhythm and Thermal Independence of Metabolic Rate in a Benthic Shark

Wheeler, Carolyn R.; Kneebone, Jeff; Heinrich, Dennis D.U.; Strugnell, Jan M.; Mandelman, John W.; Rummer, Jodie L.

doi:10.1177/07487304221107843

Cited by 6 publications

(1 citation statement)

References 62 publications

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“…Thermal effects on metabolic rate may also be a useful, non-lethal method to assess changes in organismal energetic costs. Adult epaulette shark metabolic costs do not differ between current day spring and summer mean water temperatures (25°C versus 28°C) ( Wheeler et al, 2022 ), but prolonged, chronic exposure to future ocean warming temperatures of 31°C does reduce physiological performance of embryos and neonates ( Wheeler et al, 2021 ). Indeed, chronic exposure to elevated temperatures that are well below CT max may provide a better picture of sublethal effects of ocean warming across ontogeny.…”

Section: Discussionmentioning

confidence: 99%

The upper thermal limit of epaulette sharks (Hemiscyllium ocellatum) is conserved across three life history stages, sex and body size

Wheeler

Lang

Mandelman

et al. 2022

Conservation Physiology

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Owing to climate change, most notably the increasing frequency of marine heatwaves and long-term ocean warming, better elucidating the upper thermal limits of marine fishes is important for predicting the future of species and populations. The critical thermal maximum (CTmax), or the highest temperature a species can tolerate, is a physiological metric that is used to establish upper thermal limits. Among marine organisms, this metric is commonly assessed in bony fishes but less so in other taxonomic groups, such as elasmobranchs (subclass of sharks, rays and skates), where only thermal acclimation effects on CTmax have been assessed. Herein, we tested whether three life history stages, sex and body size affected CTmax in a tropical elasmobranch, the epaulette shark (Hemiscyllium ocellatum), collected from the reef flats surrounding Heron Island, Australia. Overall, we found no difference in CTmax between life history stages, sexes or across a range of body sizes. Findings from this research suggest that the energetically costly processes (i.e. growth, maturation and reproduction) associated with the life history stages occupying these tropical reef flats do not change overall acute thermal tolerance. However, it is important to note that neither embryos developing in ovo, neonates, nor females actively encapsulating egg cases were observed in or collected from the reef flats. Overall, our findings provide the first evidence in an elasmobranch that upper thermal tolerance is not impacted by life history stage or size. This information will help to improve our understanding of how anthropogenic climate change may (or may not) disproportionally affect particular life stages and, as such, where additional conservation and management actions may be required.

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Section: Discussionmentioning

confidence: 99%

The upper thermal limit of epaulette sharks (Hemiscyllium ocellatum) is conserved across three life history stages, sex and body size

Wheeler

Lang

Mandelman

et al. 2022

Conservation Physiology

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An electrophysiological correlate of sleep in a shark

Lesku,

Libourel,

Kelly

et al. 2024

J Exp Zool Pt A

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Sleep is a prominent physiological state observed across the animal kingdom. Yet, for some animals, our ability to identify sleep can be masked by behaviors otherwise associated with being awake, such as for some sharks that must swim continuously to push oxygenated seawater over their gills to breathe. We know that sleep in buccal pumping sharks with clear rest/activity cycles, such as draughtsboard sharks (Cephaloscyllium isabellum, Bonnaterre, 1788), manifests as a behavioral shutdown, postural relaxation, reduced responsiveness, and a lowered metabolic rate. However, these features of sleep do not lend themselves well to animals that swim nonstop. In addition to video and accelerometry recordings, we tried to explore the electrophysiological correlates of sleep in draughtsboard sharks using electroencephalography (EEG), electromyography, and electrooculography, while monitoring brain temperature. The seven channels of EEG activity had a surprising level of (apparent) instability when animals were swimming, but also when sleeping. The amount of stable EEG signals was too low for replication within‐ and across individuals. Eye movements were not measurable, owing to instability of the reference electrode. Based on an established behavioral characterization of sleep in draughtsboard sharks, we offer the original finding that muscle tone was strongest during active wakefulness, lower in quietly awake sharks, and lowest in sleeping sharks. We also offer several critical suggestions on how to improve techniques for characterizing sleep electrophysiology in future studies on elasmobranchs, particularly for those that swim continuously. Ultimately, these approaches will provide important insights into the evolutionary confluence of behaviors typically associated with wakefulness and sleep.

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A wandering wedgefish illustrates the need for cooperative elasmobranch conservation in the Arabian Gulf

Bruns,

Al Hameli,

Sulanke

et al. 2024

Environ Biol Fish

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The smoothnose wedgefish Rhynchobatus laevis, a shark-like ray classified as Critically Endangered by the International Union for Conservation of Nature, has received limited research attention. To address the knowledge gaps in its spatial behaviour, this study utilised satellite monitoring of a fortuitously captured female over a 51-day period in the Arabian Gulf. Based on the resulting movement track, the individual covered a minimum distance of 712 km, traversing the exclusive economic zones of three different countries. Its track began in the United Arab Emirates, from where it headed north, entering Iranian waters, where it spent most of its time, before continuing westward across the Gulf and eventually reaching Qatari waters. Novel insights into its behaviour revealed an observation of rapid ascents over the study period. Although both diurnal and nocturnal ascents were observed, they occurred predominantly during nocturnal periods. Contrary to the prevailing belief that wedgefish are bottom-associated, the study animal spent a considerable amount of time in the water column. The use of various depths in both nearshore and offshore waters highlights elevated susceptibility to multiple types of fishing gear. This underscores the need for an international cooperative approach to the management and conservation of shark-like rays in the Arabian Gulf.

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Diel Rhythm and Thermal Independence of Metabolic Rate in a Benthic Shark

Cited by 6 publications

References 62 publications

The upper thermal limit of epaulette sharks (Hemiscyllium ocellatum) is conserved across three life history stages, sex and body size

The upper thermal limit of epaulette sharks (Hemiscyllium ocellatum) is conserved across three life history stages, sex and body size

An electrophysiological correlate of sleep in a shark

A wandering wedgefish illustrates the need for cooperative elasmobranch conservation in the Arabian Gulf

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