Abstract
In both commercial and recreational fisheries, many sharks are captured and released alive due to harvest regulations, the capture of non-target species, or conservation ethics. Nevertheless, released individuals may suffer post-release fitness loss or even mortality due to capture stress. Additionally, some of these species that would otherwise be intended for release are found dead upon capture. Understanding physiological and behavioral responses of sharks to capture stress is important for determining best fishing practices and for establishing effective management strategies. In this study, I investigated sub-lethal effects of capture through monitoring blood glucose, lactate, hematocrit and reflex impairment on four species of coastal sharks: blacktip (Carcharhinus limbatus), great hammerhead (Sphyrna mokarran), nurse (Ginglymostoma cirratum) and sandbar (Carcharhinus plumbeus). A probability of impairment score was given to each individual based off reflexes developed for this study. I further evaluated inter- and intra- specific relationships between these parameters and fight time, season, and shark size. Of the physiological parameters accessed, lactate emerged as the most significant with increases associated with fight time, shark species, and reflex impairments. Reflex indices showed significant impairment with increasing fight time with the “Jaw” reflex being most significant in all evaluations. Species-specific differences were detected in all parameters with nurse sharks consistently having the lowest values and impairments while great hammerheads had the highest. These relative differences in species-specific stress responses is consistent with relative difference in fighting behavior exhibited for these species on a fishing line as well as reported at-vessel and post-release mortality rates for these species. Collectively, these results indicate that lactate can be used as a measure of shark capture stress, jaw reflex impairments can be utilized as significant indicators of shark capture stress on a species specific basis, and that species’ ecology likely contributes to these responses both physiologically and in terms of reflex impairment. This work connects species-specific reported at-vessel and post-release mortality rates with their responses to capture by revealing trends in physiological changes and reflex impairments. The drumline capture method used likely represents a more benign fishing method compared to typical recreational and commercial fishing gears and therefore these responses are likely subdued when compared to other fishing techniques. Therefore, continued investigation is warranted to better understand the varied responses among species and different capture techniques.