Stress physiology of scalloped and great hammerhead sharks from a bottom longline fishery

The scalloped hammerhead Sphyrna lewini and the great hammerhead S. mokarran are large, coastal to semi-oceanic shark species common to waters of the US east coast where they are regularly taken in commercial and recreational fisheries, particularly the bottom longline fishery. High rates of hooking mortality and low rates of population growth are believed to have caused severe declines in the US Atlantic populations of these species. The objective of this study was to determine the physiological stress induced by bottom longline capture in both S. lewini and S. mokarran. Physiological stress was quantified using the blood biochemical indicators glucose, lactate, pH, haematocrit, sodium, potassium, calcium, chloride and magnesium, which have been demonstrated to indicate physiological stress in elasmobranchs. Each shark captured was assigned a condition factor, which was compared with the stress parameters and time on hook to quantify stress induced by different longline hook times. In S. lewini, the physiological stress parameters lactate, pH, sodium and chloride scaled with hook time, whereas in S. mokarran, only lactate was affected by hook time. In both species, water temperature affected lactate and glucose levels, as well as sodium and pH levels in S. lewini and magnesium levels in S. mokarran. These data will be useful for estimating post-release mortality of S. lewini and S. mokarran from measurements taken at the time of capture, and quantifying the physiological stress response to longline capture in both species to the Atlantic bottom longline fishery.