Negative interactions between sharks and humans are rare on a global scale. More humans are killed by toasters, cows or vending machines than are killed by sharks, and heart disease kills about a million times as many people as sharks do. However, inaccurate and inflammatory media coverage (Muter et al., 2013; Neff & Hueter, 2013) makes the problem seem worse than it really is, and that results in elected officials who want to do something about the issue. Many commonly used ‘shark control’ strategies involve killing sharks with the goal of reducing the probability of a swimmer encountering a shark.
As nearly 25% of sharks and their relatives are considered threatened with extinction by the International Union for the Conservation of Nature Red List (Dulvy et al., 2014), this strategy is unpopular with environmentalists. Additionally, many large species of sharks migrate vast distances (i.e. tiger sharks were observed to move thousands of kilometers from their capture location; Hammerschlag et al., 2012), and shark culls have been shown to be of limited effectiveness in terms of reducing local populations of these species (Simpfendorfer, Goodreid & McAuley, 2001). The cull in Hawaii did not reduce the incidence of shark bites (Wetherbee, Lowe & Crow, 1994). Electromagnetic barriers that repel sharks without harming them have shown some early promise (O'Connell et al., 2011); however, the technology is new and not widely tested. Different species of sharks have been shown to vary widely in their responses to electromagnetic fields (Godin et al., 2013), and some of the species responsible for the most shark bites have yet to be tested. A new strategy is sorely needed, a strategy that can actually reduce the rate of shark bites without harming the populations of threatened species.
The technique pioneered in Recife, Brazil may just be the new strategy we have been looking for (Hazin & Afonso, 2014). The technique itself is brilliant in its simplicity – instead of using advanced (and relatively untested) technology to attempt to repel sharks or nondiscriminatory nets that kill other threatened sea life as bycatch, the team simply caught sharks and moved them to where they would not pose a threat to swimmers. The use of baited drumlines with large hooks (instead of nets) results in low bycatch. Giving the drumlines a relatively short soak time results in low capture mortality (Hazin and Afonso report approximately 100% survival of protected species). As it does not result in killing the sharks, environmentalists will not object. As it successfully reduces shark bites (Hazin and Afonso reported a 97% decrease), it should appease politicians and the media eager to ‘do something’ about the perceived threat of sharks.
Huxley once said ‘how extremely stupid not to have thought of that’ of Darwin's theory of evolution by natural selection, and many in the shark research world feel similarly of the strategy presented in Hazin & Afonso (2014). It is important to consider the potential limitations, though, despite the exciting preliminary results. While drumlines are inexpensive and can be deployed on a large scale, a short soak time requires a crewed boat frequently checking the lines. A single boat and crew could manage a relatively small area such as that used in this study, but this expense will rapidly increase as this method is scaled up to larger geographic areas. Additionally, if the area we are removing sharks from represents an important habitat for them (a migration corridor, mating aggregation area or nursery), they will likely keep coming back. If this strategy works in other regions, though, this has the potential to be a revolution in shark control.