The team had already ascertained that C8 barium-ferrite (BaFe12O19) permanent magnets successfully repelled bull sharks, but were unsure as to the success magnets would have on repelling sharks which are more reliant on their visual system. The aims of this study were to ascertain whether magnets would successfully repel visually impaired juvenile lemon sharks (Negaprion brevirostris).
The researchers hypothesised that restricting the vision of lemon sharks would lead to a greater reliance on short range senses such as electro reception - an effect known as context dependent switching. In the wild the visual field of a marine animal could be restricted by bad visibility caused by environmental conditions such as turbidity. In this instance,
The sharks were visually impaired using a short term, simple surgery technique to suture closed the nictitating membrane of the eye. Once the experimental phase was completed, the sutures were removed, restoring the vision of the sharks. All sharks showed successful recovery post-experimentation.
The experimental area was separated into different compartments, both with and without magnets present. The sharks were divided into groups with differing levels of visual impairment. By assessing the behaviour of the different shark types to the magnets, the researchers were able to assess what impact visual impairment had on context dependent switching of senses.
Visually impaired sharks did indeed enter areas with magnets less frequently than sharks with visual ability. These results suggest that magnetic repellents would be more successful when sharks are visually impaired, and this could translate to the visual impairment experienced in turbid waters. Magnets could be an appropriate method of deterring all species of sharks from entering turbid regions, and not just those which are less reliant on their visual system to begin with.
Connell, C., Guttridge, T., Gruber, S., Brooks, J., Finger, J. and He, P. (2014) Behavioral modification of visually deprived lemon sharks (Negaprion brevirostris) towards magnetic fields. Journal of Experimental Marine Biology and Ecology 453:131-137
