The effect of magnets on the behaviour of draughtboards sharks (Cephaloscyllium laticeps)
Chinnappa, E and Hansen, W and Maynard, D and Ngwenya, E and Rahman, MA and Rawlinson, N and Westlake, E and Williams, MI, The effect of magnets on the behaviour of draughtboards sharks (Cephaloscyllium laticeps), ASFB-OCS Joint Conference Abstract Book, 04-07 September, Hobart, Tasmania, pp. abstract 217. (2016) [Conference Extract]
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Draughtboard sharks (Cephaloscyllium laticeps) are a major bycatch in the Tasmanian Southern Rock Lobster fishery (TSRLF). Magnets are effective at deterring sharks around a range of different fishing methods and were tested as an option for reducing the ingress of draughtboard sharks into pots. Over the course of four separate (honours) projects conducted by students from the Australian Maritime College and the Institute for Marine and Antarctic Studies, we measured the reactions of draughtboard sharks to strontium ferrite and neodymium-iron-boron magnets. Two studies were conducted in the natural habitat of the draughtboard sharks and two were controlled experiments with the sharks held in tanks. The two field studies produced inconclusive results due to small sample sizes and the inability to identify the individual sharks that approached the magnets. In the controlled experiments we were able to measure changes in the behaviour of individual draughtboard sharks in close proximity to a magnet, a control and procedural control. The behaviour of the individual sharks varied. Overall, the results of the most recent tank experiment showed that avoidance reactions were observed at the magnet in 10 out of the 12 sharks but for only 6% of the approaches to the magnets. This would suggest that it is unlikely that magnets will significantly deter draughtboard sharks in the TSRLF, however the next proposed series of controlled experiments will involve observing the behaviour of draughtboard sharks around a pot with magnets fitted to the entrance. This poster outlines the relative merits of the different experimental approaches used. It is suggested that measuring the underlying behaviour that is predicted to decrease the catch rates of bycatch species should be considered as an initial step before testing the proposed mitigation measure in a commercial fishery.