Abstract
Understanding the stress responses of sharks to recreational catch and release fishing has important management and conservation implications. The blacktip shark Carcharhinus limbatus is a popular recreational species targeted throughout the western, central and eastern Gulf of Mexico (Gulf) yet it is unclear what levels of physiological stress result from catch-release fishing practices with hook and line gear and if the stress levels result in post-release mortality. This study correlates physiological response to stress through blood chemistry analysis and examines post-release behaviour of adult blacktip sharks caught to determine post-release mortality rates. Release behaviour was determined by pop-up satellite archival transmitting (PSAT) tags that record temperature, depth and light level data. To quantify physiological stress levels, blood samples were collected from 52 blacktip sharks and a suite of metabolic and osmotic markers were measured. Thirty-six of those blacktip sharks were also outfitted with a PSAT tag yielding time-at-large from 3 to 180days. Of the 36 tags, 22 (61%) provided sufficient data to confirm post-release fate and 11 (31%) were recovered providing high-resolution data. Tag data suggests a post-release morality rate of 22.7% (95% confidence interval 7.8-45.4%), with mortality occurring within minutes (immediate mortality) to over 12h post-release (delayed mortality). Compared to survivors, immediate mortalities exhibited significantly higher lactate (median 2.8mmol/Lsurvivor vs 5.9mmol/Limmediate mortality) and significantly lower hematocrit (median 24.4% survivor vs 14% immediate mortality) levels, but no difference was detected between survivors and delayed mortalities. Higher mortality in the western (30%) compared to the central (20%) Gulf may be due to shark handling. All PSATs from mortalities (N = 5) were recovered, and archived data revealed evidence of tag ingestion by predators. Results suggest reduced fight time, decreased handling time and limited air exposure provide blacktip sharks the best survival chances after release by recreational anglers.
Highlights
Sharks are popular target species of recreational anglers due to their large size and strong fighting and jumping power when captured by rod and reel (Babcock 2009)
The blacktip shark Carcharhinus limbatus is a popular recreational species targeted throughout the western, central and eastern Gulf of Mexico (Gulf) yet it is unclear what levels of physiological stress result from catch-release fishing practices with hook and line gear and if the stress levels result in post-release mortality
Recreational post-release mortality rates for blacktip sharks range from 9.7% for sharks captured by experienced charter captains in the eastern Gulf of Mexico (Whitney et al 2017) to 18.5% for blacktip sharks caught by common recreational anglers off the east coast of the USA (Weber et al in press)
Summary
Sharks are popular target species of recreational anglers due to their large size and strong fighting and jumping power when captured by rod and reel (Babcock 2009). As recreational fishing for sharks continues to increase in popularity (Ajemian et al 2016, Gibson et al 2019) it is essential to quantify how catch and release practices influence shark physiology, survival and populations. Recreational post-release mortality rates for blacktip sharks range from 9.7% for sharks captured by experienced charter captains in the eastern Gulf of Mexico (Whitney et al 2017) to 18.5% for blacktip sharks caught by common recreational anglers off the east coast of the USA (Weber et al in press). This study quantifies physiological stress associated with conventional recreational angler rod and reel capture of blacktip sharks using blood chemistry analysis and represents the first attempt to estimate regional post-release mortality rates using pop-up satellite transmitting tags for sharks captured in the eastern, central and western Gulf of Mexico
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