Now why would anybody want to repel sharks? Well it turns out that sometimes not only can they be a nuisance - by getting themselves accidentally caught up in fishing gear - but some people get a bit nervous when there are sharks around and would prefer them to just darn well stay away when they are trying to go for a swim. People like Colin Barnet the Premier of WA - these people get so nervous about the idea of sharks being in the water when they are going for their morning swim that it makes them stay out of the water - oh no wait, sorry. Actually they still go into the water but they just want to try and kill all the sharks in the ocean so they feel safer when they go for their morning swim. It turns out we can't just dispatch of idiots like this, so some hard working scientists are looking at ways of creating repelling barriers which will be shark friendly (unlike drumlines and shark nets) and will minimise shark/human interaction.
Following on from a series of previous works (The Shark Post, 14th Feb, The Shark Post - 13th Jan, Craig P. O'Connell has been continuing investigations into the use of barium-ferrite permanent magnets for repelling sharks. Previous work showed strong evidence that fish with electrosensory capabilities - such as elasmobranchs - were usually successfully deterred by magnets. A key piece of research showed that bull sharks (Carcharhinus leucas) in particular could be repelled by magnets - a very interesting result as the lovely bull shark is one of the species which has got people such as Mr. Barnett so hot under the collar (you can read about my experiences of diving with these very awesome sharks here: The Shark Post, 11th Jan).
Like any good scientific ideas, the concept of using magnets as shark barriers requires a lot of investigation before it can become a reality. The latest research to come out of this project involved assessing whether or not other marine organisms might also be affected by the presence of magnets in the water (whilst it might be great having a magnet which repels sharks incorporated in your fishing gear, it's not so great if it turns out to repel all the other fish you are trying to catch too!)
C.P. O'Connell set up a series of experiments in the Bahamas to assess whether the reaction of teleost (bony fish) was significantly different to that of elasmobranchs (our cartilaginous friends). The research focused on ascertaining reactions of both types of fish to magnetic barriers and bait which was associated with a magnet. The results showed that teleost fish did not exhibit significant changes in their behaviour towards the magnets, whilst the majority of the shark species did. Not only did this study reaffirm the idea that magnets could be used to keep certain species of sharks away from fishing vessels and popular beaches, it also lent strength to the argument that behavioural impacts on other marine organisms would be minimal if magnets were deployed in the wild. Naturally there is still a long way to go before we have magnetic shark nets along our beaches, but so far the findings suggest that this could one day be a viable alternative to shark nets!
O'Connell, C.P. and He, P. (2014) A large scale field analysis examining the effect of magnetically-treated baits and barriers on teleost and elasmobranch behavior. Ocean & Coastal Management. 96: 130-137
