PHYSIOLOGICAL STRESS RESPONSE AND POST-RELEASE MORTALITY OF THE BONNETHEAD, Sphyrna tiburo
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Cashour, Jacob Elias
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Abstract
No estimates of recreational post-release mortality (PRM) exist for Bonnethead, Sphyrna tiburo and data pertaining to their physiological stress response following capture is limited. To determine S. tiburo mortality rates in the South Carolina charter recreational fishery, individuals were fitted with acoustic transmitters from July 2020 to September 2021 following recreational capture. Recreational angling took place in the North Edisto River within a gated acoustic receiver array managed by the South Carolina Department of Natural Resources. Prior to tagging, a blood sample was taken from each shark examined with a portable blood analyzer to measure lactate, bicarbonate, and pH levels. Environmental conditions, handling time, morphometrics, as well as gear-specific data were recorded for all individuals. Additionally, to obtain a greater understanding of the response of S. tiburo to temperature and hypoxia, a subset of 27 individuals were utilized for further analyses of blood following exhaustion on rod-and-reel. Analysis of acoustic telemetry data suggests a PRM rate of 9.4% for Sphyrna tiburo from 64 capture events. Hook location and release condition had significant impacts on the potential survival of captured sharks, as 33.3% of foul hooked individuals, and over 36% of individuals assigned a release condition of ‘fair’ or ‘poor’, died following release. Strong correlations were found between handling time, pH, bicarbonate, and lactate levels. Sea surface temperature and aerial exposure also demonstrated significant relationships with each of these biochemical stress indicators. Individuals experiencing PRM demonstrated significantly higher lactate and lower blood pH compared to sharks surviving release. Significant differences in the expression of heat shock protein 70 occurred with increases in temperature and decreases in oxygen levels. Overall, this study aided in determining the anthropogenic effects of recreational fishing on S. tiburo and provided levels of various biochemical factors expressed in this species following exposure to biotic and abiotic stressors.