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RESEARCH ARTICLE
Contents Vol 60(9)

Do elasmobranch reactions to magnetic fields in water show promise for bycatch mitigation?

Damian P. Rigg A , Stirling C. Peverell B , Mark Hearndon C and Jamie E. Seymour A D
+ Author Affiliations
- Author Affiliations

A School of Marine and Tropical Biology, James Cook University, 1-88 McGregor Road, Smithfield, Qld 4878, Australia.

B Queensland Department of Primary Industries and Fisheries, 38-40 Tingira Street, Portsmith, Cairns, NT 4870, Australia.

C Northern Territory Department of Primary Industry Fisheries and Mines, GPO Box 3000, Darwin, NT 0801, Australia.

D Corresponding author. Email: jamie.seymour@jcu.edu.au

Marine and Freshwater Research 60(9) 942-948 https://doi.org/10.1071/MF08180
Submitted: 17 June 2008  Accepted: 1 January 2009   Published: 22 September 2009

Abstract

Elasmobranchs are under increasing pressure from targeted fisheries worldwide, but unregulated bycatch is perhaps their greatest threat. This study tested five elasmobranch bycatch species (Sphyrna lewini, Carcharhinus tilstoni, Carcharhinus amblyrhynchos, Rhizoprionodon acutus, Glyphis glyphis) and one targeted teleost species (Lates calcarifer) to determine whether magnetic fields caused a reaction response and/or change in spatial use of experimental arena. All elasmobranch species reacted to magnets at distances between 0.26 and 0.58 m at magnetic strengths between 25 and 234 gauss and avoided the area around the magnets. Contrastingly, the teleosts showed no reaction response and congregated around the magnets. The different reactions of the teleosts and elasmobranchs are presumably driven by the presence of ampullae of Lorenzini in the elasmobranchs; different reaction distances between elasmobranch species appeared to correlate with their feeding ecology. Elasmobranchs with a higher reliance on the electroreceptive sense to locate prey reacted to the magnets at the greatest distance, except G. glyphis. Notably, this is the only elasmobranch species tested with a fresh- and salt-water phase in their ecology, which may account for the decreased magnetic sensitivity. The application of magnets worldwide to mitigate the bycatch of elasmobranchs appears promising based on these results.

Additional keywords: ferrite magnet, gill-net.


Acknowledgements

This study was undertaken as part of the Development of a Gulf-Based Natural Resource Monitoring Program, with Sawfish as the Initial focus by Queensland Department of Primary Industries and Fisheries. Thanks to Cairns Marine for supplying test animals and facilities, Associate Professor Andrew Krockenberger and Dr Colin Simpfendorfer for helpful suggestions on the paper and Richard Fitzpatrick of Digital Dimensions for technical assistance. Grateful thanks also are extended to Dr Allan W. Stoner for reviewing the manuscript and for his helpful and insightful comments. All experiments were performed in compliance with the Australian Code of Practice for the Care and Use of Animals for Scientific Purposes and the Queensland Animal Care and Protection Act 2001. Ethics Approval: A1263.


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