Estimating oxygen uptake rates to understand stress in sharks and rays

Abstract

Elasmobranch populations face worldwide declines owing to anthropogenic stressors, with lethal and sub-lethal consequences. Oxygen uptake rates ($\dot{M}$O₂, typically measured in mg O₂ kg⁻¹ h⁻¹) can be quantified as proxies of whole-organism aerobic metabolic rates and are relevant to fisheries management and conservation through aerobic performance’s relationship with fitness and spatial ecology. The purpose of this review was to better understand how $\dot{M}$O₂ has been and can be applied to predict how elasmobranch populations will respond to current and future anthropogenic stressors. We identified 10 studies spanning 9 elasmobranch species that quantified $\dot{M}$O₂ to understand elasmobranch populations’ responses to exposure to anthropogenic stressors. Studies measuring responses to climate change stressors (ocean warming and acidification, declining oxygen content, increasing storm frequency) were most common. Studies with relevance to fisheries stressors used $\dot{M}$O₂ to approximate energetic costs of capture and estimate recovery times in bycatch scenarios. Ecotourism encounters were investigated in the context of increases in energetic requirements owing to anthropogenic disruption of diel activity cycles. Furthermore, we discuss how an understanding of $\dot{M}$O₂ in elasmobranchs has been and can be applied to predict populations’ responses to anthropogenic stressors with deliverables for improving species management and conservation. Specifically, $\dot{M}$O₂ can be applied to predict population-level responses to stressors by quantifying associations between $\dot{M}$O₂ and fitness-related processes, spatial ecology, and impact on ecosystem function (via bioenergetics modelling). This review is meant to serve as a call-to-action to further bridge the gap between experimental biology and elasmobranch conservation in the “good Anthropocene”.