Australasian Science Magazine

By Ryan Kempster and Shaun Collin

Are shark attacks on the rise, and what can you do to minimise your risk this summer?

In light of the most recent shark bite fatality in Western Australia (WA) last week, there have been renewed calls for a cull of large sharks to protect ocean users. Environment minister Greg Hunt has said he wants to reduce the risk of attacks. So what is the best way to reduce that risk?

Are shark bites increasing?

There is no denying that each of these events is a tragedy and our sympathy is, of course, with the family and friends of the victims. However, based on statistical data, the number of shark related fatalities is negligible when you consider the vast and increasing number of swimmers entering our coastal waters every year.

Research has shown the number of shark bite incidents occurring each year appears to be directly related to the amount of time people spend in the sea. Given that Western Australia has the fastest population growth of any Australian state, there is likely to be an increasing number of people venturing out into our coastal waters every year. Thus, the likelihood of someone encountering a shark increases and with it a corresponding increase in shark bite incidents.

Politicians and the public are often quoted in the media saying shark numbers in WA have increased. But most experts would agree that there is no evidence to support such a statement.

Data gathered by Surf Life Savers WA has been used to suggest an increase in the number of sharks in WA, by stating that more sharks were sighted in 2012/13 (285 sharks) than in 2011/12 (247 sharks).

However, when you account for the number of hours that the helicopter patrols were out looking for sharks (2012/13: 751 hrs; 2011/12: 620 hrs) we find that they sighted the same number of sharks per hour of patrolling (approximately 1 shark every 2.5 hrs).

In fact, research shows that the number of attacks per million people in Australia almost halved from approximately 60 per million people between 1930/1939 to approximately 30 per million people between 2000/2009.

Does culling work?

So often the argument in favour of a cull comes down to the emotional question of who is more important: a human or a shark. Rather, we need to ask the question, will culling sharks actually reduce the risk of an attack?

The answer is no. In fact, when shark culling was carried out in Hawaii, between 1959 to 1976, over 4,500 sharks were killed and yet there was no significant decrease in the number of shark bites recorded.

Culling has been the primary shark mitigation policy of the New South Wales Government for over 60 years, through the use of “shark” nets. But a report by the Department of Primary Industries showed that 24 of the 38 (63%) attacks in the state, between 1937 and 2008, occurred at netted beaches.

Pre-emptively killing sharks is a response based on emotion rather than of scientific data.

How to reduce personal risk

We take a calculated risk whenever we enter the ocean, but the risk is quite small when compared to other daily activities. For example, new research shows that rip currents are the cause of an average 21 confirmed human fatalities per year in Australia, compared with 7.5 for cyclones, 5.9 for bushfires, 4.3 for floods, and 1 for sharks.

With the correct information, we can make an objective judgement as to whether or not we accept the risk to enter the oceans.

The WA Department of Fisheries recently released a report on how to reduce your personal risk of being bitten by a shark (and you can find more information at the International Shark Attack File).

1. Stay out of the water if sharks have been sighted in the area.

2. Stay close to shore (within 30m of the water’s edge).

3. Don’t go in the water alone (stay in groups).

4. Avoid water temperatures lower than 22C.

5. Avoid water depths of greater than 5m when swimming or surfing.

6. Avoid swimming after heavy storms, or in low light conditions (dusk and dawn).

7. Avoid swimming if there are seals, dolphins, whales or baitfish nearby.

What the government can do

The WA Government are in a difficult situation. They genuinely want to protect ocean users, but at the same time they are well aware there is no “magic bullet” to prevent shark attacks across the large expanse of the WA coastline.

Their investment in monitoring and research has been a very positive step towards reducing shark bite incidents in the region, but the use of lethal control measures and the threats of a major cull of sharks is not the answer.

Instead, we need to better understand exactly what causes sharks to bite people, what factors are responsible for them venturing closer to shore and more about their biology and life history. Recent research has found, for example, that sharks' diving behaviour is affected by temperature and the moon, that female white sharks have different movement patterns to males, and that Australian white sharks have home territories they always return to.

This kind of research helps us better understand where sharks will be and how they’re likely to behave. More of the same could help us develop strategies to coexist with these important apex predators and continue to enjoy the ocean safely.

The WA Government should also consider placing more emphasis on educating people about the risks, such as the times of day and conditions under which attacks are most likely to occur.

They could also put warning signs at beaches known to be frequented by “dangerous” sharks. We are unaware of a single beach in WA that has information boards related to the risks associated with encountering potentially dangerous sharks. This strategy is common practice in California and other places frequented by large sharks.

We will never completely prevent shark attacks, however, with better education and improved investment in monitoring and research we can reduce the risk and frequency of these tragic events.

Ryan Kempster is a shark biologist at the University of WA, and founder of the shark conservation group Support Our Sharks (www.supportoursharks.com). Shaun is a Winthrop Professor at The University of Western Australia and a Western Australian Premier’s Research Fellow. This article was originally published at The Conversation.