The Physiological Stress Response of Juvenile Nurse Sharks (Ginglymostoma cirratum) to Catch-and-Release Recreational Angling

Nurse sharks (Ginglymostoma cirratum), especially juveniles, are often encountered by near-shore and shore-based recreational fishers and released alive, with unknown physiological effects. In cartilaginous fishes, physiological parameters such as lactate, glucose, and hematocrit have been shown to exhibit a positive relationship with increasing time spent hooked (“fight time”) for several species. Nurse sharks are suggested to exhibit minimal behavioral and physiological responses to capture, largely based on studies of adults using commercial or scientific fishing methods. In this study, 27 individuals (across 31 angling events) were caught using hook and line fishing methods. Over a 30-min period, 4 blood samples were taken with variable time intervals between sampling. Lactate was found to be significantly affected by blood draw number, fight time, and temperature. Significant relationships were also detected between blood draw number and glucose and hematocrit, while osmolality was only affected by fishing site. These results suggest juvenile nurse sharks exhibit a greater physiological stress response when exposed to recreational angling than adults captured with other fishing methods.  In addition, this work was meant to validate the use of field POC devices (Lactate Pro meter and Accu-Chek glucose meter) designed for human blood in collecting physiological data from nurse sharks by comparing meter readings to values from laboratory assays. Results revealed the Lactate Pro meter predictably overestimated lactate concentrations and that differences can be compensated for by using an adjustment curve. Conversely, only a weak relationship was found between the Accu-Chek glucose meter and laboratory values, suggesting the machine may not be reliable for measuring glucose values in nurse sharks. While more research is needed to determine the effects of capture stress on the overall health, fitness, and survival of juvenile nurse sharks, these results highlight the potential for greater vulnerability in juvenile elasmobranchs.