Physiological responses to capture, handling and tagging in the critically endangered flapper skate (Dipturus...

Catch-and-release angling is a popular recreational pastime and an essential component of many fish research programmes. Marked physiological disturbances have been documented in elasmobranchs in response to angling and handling, but skates and rays remain understudied. Here, we describe for the first time the physiological responses of the critically endangered flapper skate (Dipturus intermedius) to angling, handling and tagging in Scotland. Sixty-one skate were captured by angling as part of a tagging research programme. We assessed individual health, measured blood parameters at two time points (post-capture and prior to release) and recorded heart and respiratory rates during handling and the surgical insertion of acoustic tags. Injuries or infections were identified in 10% of individuals and attributed to prior angling in two cases. Skate generally experienced a mild metabolic acidosis characterized by decreases in blood pH and bicarbonate and increases in lactate and glucose. Respiratory acidosis characterized by limited increases in PCO₂ was also observed. The degree of acidosis was greater with warmer sea temperatures and longer fight times, and worsened during the time that skate were handled on deck. Heart rates during handling were negatively associated with body size, positively associated with temperature and also linked to time on the line. Taken together, our results suggest that elevated fight times and temperatures increase the physiological stress experienced by rod and reel-caught flapper skate. Efforts to reduce fight times and minimize heat exposure (including shading, irrigation and reduced handling time) should be beneficial for skate.