Shark attacks – a brief discussion

Thirteen. That is the number of shark attacks currently registered with Taronga Zoo’s Australian Shark Attack File for 2015 in New South Wales. This is the highest the number  has been in nearly 200 years of record keeping. With the peak summer season some weeks away and a high number of people expected to visit beaches, community pressure is mounting on policy makers to stop shark related fatalities. In response, the NSW government has convened a summit at Taronga Zoo, bringing together national and international experts to discuss strategies to limit human-shark encounters. Before any strategies are implemented, however, we must first understand why there has been an increase in the number of human-shark encounters. Three common theories have been debated and, while not comprehensive, provide a general insight into the issue. These three theories are interrelated and discussed below.

Firstly, population densities along the coasts have been increasing. This means that more people are likely to visit beaches and engage in water based recreational activities. Surfing, snorkeling, spear fishing, scuba diving and swimming have become increasingly popular. As more people spend time in the water, the likelihood of encountering a shark increases. Evidence suggests that surfers and bodyboarders appear to be most at risk. This may be related to surfers being most active during dawn and dusk, times when sharks are thought to be most active. However, sharks are opportunistic feeders and there is no set time of day where activity can be correlated with human interaction. This unpredictability was broadcast on live television as Australian surfer, Mick Fanning was attacked by a shark in broad daylight, while competing in a tournament in South Africa. Surfers and bodyboarders are often targets because it is believed that the silhouettes they cast paddling on the surface resemble that of seals, a popular prey for many species of sharks.

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Australian surfer Mick Fanning’s encounter with a shark earlier this year. Image reproduced from news.com.au (2015).

Secondly, as coastal populations increase and beaches become overcrowded, more people seek to escape by venturing to more remote beaches. Australia is home to nearly 35 000 km of coast, which is a significant challenge in terms of beach patrols and medical assistance during emergencies. Indeed, 90% of shark attacks over the past two decades have occurred in less populated areas (West, 2011).

Thirdly, more sharks are being found closer to shore and understanding why this is the case is important. A common misconception is that global shark populations are increasing and competition is driving them closer to shore. However, this is not the case as many species of sharks are critically endangered. It is largely believed that years of large-scale, intensive commercial fishing has been driving down the wild-fish stocks which form part of the shark’s diet. As such, sharks are altering their hunting behaviour by foraging closer to shores and estuaries. Schools of fish, particularly bait fish, become easy targets for sharks and identifying them has become part of the education campaign in Australia to minimise human-shark interactions. Bait fish depend on warm water for survival and move up and down the east coast. Entire beaches have been closed to public once bait fish are spotted such as in the Gold Coast earlier this year. By contrast, during the cooler months, the sharks follow migrating whales up and down the east coast.

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Shark caught breaching the surface as it feeds on bait fish in far north Queensland. Image reproduced from The Courier Mail (2010). Image credit Justin Duggan

With these three common theories in mind, we now move towards discussing some of the proposed minimisation strategies. Some strategies have been in place for many years, while some are more recent. The most common strategy in NSW has been the use of shark nets, which have been used in the state since 1937. Currently, fifty beaches between Newcastle and Wollongong have shark nets (NSW Department of Primary Industries, unknown). Generally speaking, shark nets of various sizes are suspended in the water, forming a barrier between the sharks and the beaches. While the concept of shark nets are simple, the evidence supporting their effectiveness still remains ambiguous.

In its annual performance report for 2014 – 2015, the NSW Department of Primary Industries found that of the ‘189 marine interactions’ with shark nets, only ‘44 were with targeted shark species’ (Department of Primary Industries, 2015). One of the most common consequence of using shark nets is that marine animals such as dolphins, turtles, whales and sea-birds can also become trapped in them. The NSW Department of Primary Industries own analysis shows that of the ‘189 marine encounters’ with shark nets, ‘73 were released alive’, while the fate of the other 116 marine animals or 60% remains unknown. If we were to assume that the 116 marine animals had died (very likely) while trapped in the shark nets then no doubt, the rotting carcases might attract the very sharks the nets are seeking to deter, ultimately becoming an expensive exercise in placebo.

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Decomposing carcass of marine animal caught in shark net. Image reproduced from Channel 7 (2015).

It is important that any strategy implemented to minimise shark attacks is careful and considered. This came to light when the West Australian government introduced active culling of sharks after a fatal attack at Cottesloe beach. A thirteen week trial was introduced at a cost of $1.3 million, where a reported 150 sharks were caught using drum lines, 50 of which were killed. Reports also surfaced that the carcasses of the sharks were being dumped offshore, which may attract other sharks to the area. After the trial, the strategy was dumped after the West Australian Environmental Protection Agency found that the evidence supporting culling was weak. Not only does a lethal response have limited effectiveness, it often lacks community support. This is reflected in a recent survey by the University of Sydney’s Dr. Christopher Neff who found that 80% of locals in Ballina (the site of the latest fatal shark attack in NSW) opposed culling of sharks.

The question that policy makers and the general public are grappling with is what an appropriate response to minimising human-shark interactions should look like. Interestingly, some of the most effective mechanisms that have been discussed at the shark summit at Taronga Zoo have already been operating for some time. First is the expansion of the tagging and monitoring of sharks. Not only will this provide an ‘early warning’ system for beach goers, but the data will also help in supplementing current gaps in scientific knowledge. Secondly, aerial surveys being conducted by services such as the Westpac Life-saver Rescue (and similar aerial patrol services) should also be expanded.

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Aerial shark patrol. Image reproduced from Sydney Morning Herald (2015). Image credit, Adam McLean.

Additional strategies such as electronic buoys, shark detecting sonar technology, cables and shark deterrent wetsuits can also form part of the response, once they reach maturity. The third and final strategy is educating the public, especially tourists, about beach and shark safety. Ultimately, it is important to understand that human-shark interactions cannot be completely prevented as coastal populations expand and shark hunting behaviours change, but much can be done about  protecting both humans and sharks.

References

NSW Department of Primary Industries., (unknown). NSW Shark meshing (bather protection) publications, http://www.dpi.nsw.gov.au/fisheries/info/sharks/meshing, (viewed, 29.9.15)

NSW Department of Primary Industries., (2015). Shark meshing (bather protection) 2014 – 2015 annual performance report, http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0007/571750/shark-meshing-bather-protection-program-2014-15-annual-performance-report.pdf, (viewed, 29.9.15)

West, G., (2011). Changing patterns of shark attacks in Australian waters, Marine and Freshwater Research, vol. 62, pg. 744 – 754.

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