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Connecting post-release mortality to the physiological stress response of large coastal sharks in a commercial longline fishery

Whitney, N.M., Lear, K.O., Morris, J.J., Hueter, R.E., Carlson, J.K. and Marshall, H.M. (2021) Connecting post-release mortality to the physiological stress response of large coastal sharks in a commercial longline fishery. PLoS ONE, 16 (9). Art. e0255673.

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Abstract

Bycatch mortality is a major factor contributing to shark population declines. Post-release mortality (PRM) is particularly difficult to quantify, limiting the accuracy of stock assessments. We paired blood-stress physiology with animal-borne accelerometers to quantify PRM rates of sharks caught in a commercial bottom longline fishery. Blood was sampled from the same individuals that were tagged, providing direct correlation between stress physiology and animal fate for sandbar (Carcharhinus plumbeus, N = 130), blacktip (C. limbatus, N = 105), tiger (Galeocerdo cuvier, N = 52), spinner (C. brevipinna, N = 14), and bull sharks (C. leucas, N = 14). PRM rates ranged from 2% and 3% PRM in tiger and sandbar sharks to 42% and 71% PRM in blacktip and spinner sharks, respectively. Decision trees based on blood values predicted mortality with >67% accuracy in blacktip and spinner sharks, and >99% accuracy in sandbar sharks. Ninety percent of PRM occurred within 5 h after release and 59% within 2 h. Blood physiology indicated that PRM was primarily associated with acidosis and increases in plasma potassium levels. Total fishing mortality reached 62% for blacktip and 89% for spinner sharks, which may be under-estimates given that some soak times were shortened to focus on PRM. Our findings suggest that no-take regulations may be beneficial for sandbar, tiger, and bull sharks, but less effective for more susceptible species such as blacktip and spinner sharks.

Item Type: Journal Article
Murdoch Affiliation(s): Centre for Sustainable Aquatic Ecosystems
Harry Butler Institute
Publisher: Public Library of Science
Copyright: © 2021 Whitney et al.
URI: http://researchrepository.murdoch.edu.au/id/eprint/62346
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