Marine and Freshwater Research Marine and Freshwater Research Society
Advances in the aquatic sciences
RESEARCH ARTICLE

Physiological response and immediate mortality of gill-net-caught blacktip reef sharks (Carcharhinus melanopterus)

Derek R. Dapp A C , Charlie Huveneers B , Terence I. Walker A and Richard D. Reina A

A School of Biological Sciences, Monash University, Wellington Road, Clayton, Vic. 3800, Australia.

B School of Biological Sciences, Flinders University, Sturt Road, Bedford Park, SA 5042, Australia.

C Corresponding author. Present address: Fish Management Program, Washington Department of Fish and Wildlife, 1111 Washington Street Southeast, Olympia, WA 98501, USA. Email: derek.dapp@dfw.wa.gov

Marine and Freshwater Research - http://dx.doi.org/10.1071/MF16132
Submitted: 10 April 2016  Accepted: 6 December 2016   Published online: 13 February 2017

Abstract

To investigate factors contributing to immediate mortality in gill-net-caught elasmobranchs, we caught and blood sampled a total of 64 sharks and rays. Blacktip reef sharks (Carcharhinus melanopterus) were the most commonly caught species and had significantly elevated plasma lactate (mean 23.3 mM) and potassium (mean 6.2 mM) concentrations following capture, suggesting physiological disturbance. The overall immediate mortality rate of C. melanopterus was 38% and mortality was significantly influenced by body size, but not location of entanglement or sex. Of the other species caught, nervous sharks (Carcharhinus cautus) were of particular concern, because this species is often caught as bycatch by gill-net fisheries throughout its range and experienced high immediate mortality rates when captured (66%; n = 12) in the present study. The results suggest that juvenile C. melanopterus are particularly susceptible to gill-net-related mortality and that fisheries management strategies for C. melanopterus bycatch should focus on reducing the likelihood of juvenile sharks encountering this gear. Given that this species is not currently considered to be threatened with extinction, population monitoring should be performed such that the suggested regulations can be implemented if populations decline to levels threatening the conservation status of the species.

Additional keywords: at-vessel mortality, biochemistry, bycatch mortality, incidental capture.


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