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

Abstract

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 (ṀO2 ; 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. ṀO2 was measured in pregnant females, before (prestress ṀO2 ) and after trawling simulation (after-capture ṀO2 ), and again after females gave birth (postpartum ṀO2 ). After-capture ṀO2 was 31.7% lower than ṀO2 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 ṀO2 was 78.5% higher than postpartum ṀO2 . Capture simulation decreased ṀO2 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.