Influence of female reproductive state and of fishing-capture stress on the oxygen uptake rate of a viviparous elasmobranch.

In animals discarded after a fishing capture event, the elicited stress response necessary to ensure their survival is energetically costly. This energy is diverted from other important biological activities, including growth and reproduction, possibly impairing them. Given that elasmobranchs are among the most threatened vertebrate groups, estimating capture-induced energetic changes and comparing these variations to the energy requirements of pregnancy maintenance is necessary. In pregnant southern fiddler rays (Trygonorrhina dumerilii), we measured changes in oxygen uptake rate (ṀO ; a proxy for metabolic rate and energy usage) in response to trawling simulation and air exposure, and estimated the oxygen requirements of sustaining late-term pregnancy and embryos. ṀO was measured in pregnant females, before (prestress ṀO ) and after trawling simulation (after-capture ṀO ), and again after females gave birth (postpartum ṀO ). After-capture ṀO was 31.7% lower than ṀO measured in minimally stressed females, suggesting a reduction in energy expenditure. This reduction is likely triggered by an initially excessive energetic investment in the stress response, and is aimed at shutting down nonessential activities to redirect energy to processes fundamental for survival. Prestress ṀO was 78.5% higher than postpartum ṀO . Capture simulation decreased ṀO to values similar to those observed postpartum, suggesting a capture-induced reduction in oxygen and energy allocation to pregnancy and embryonic respiration, which could be associated with reproductive impairments. These data, by better estimating the impact of capture and discard on energetic requirements and reproductive fitness, may support the introduction of area and/or seasonal closures to fishing.