02:02pm Monday 21 August 2017

Proof still required that shark culling works

Should we be setting up a program to kill great white sharks off the coast of Western Australia? It’s a question that is creating much debate since the recent announcement by the WA Government of new measures to mitigate risks of shark attacks after the recent attacks along the coast.

Not surprisingly, the debate has created division in the community, now and over a number of years. The debate effectively boils down to public safety versus the protection of a threatened species.

Certainly, the threat to public safety appears to be increasing over the last few years due to the increased number of shark attacks off our coasts. It has been argued that the cause of this relates to an increase in the numbers of sharks, and presumably, an increase in the population size. However, there is no evidence that this is the case, as indicated in a 2013 report on the recovery of white sharks by the Australian Government.

This is perhaps not surprising, given that they are slow growing, late maturing and produce few offspring, so it takes many years for them to recover from exploitation. An alternative, and more plausible explanation of the increased shark attacks, is the increasing number of people spending time in our coastal waters. Reflecting the population increase and Australian’s love of the coast, more people are surfing, kite surfing, diving, canoeing, and so on, leading to an increasing number of encounters with a shark.

With no evidence of recovery by the white shark population, we therefore need to be very cautious of culling this species that is classified as vulnerable and is fully protected in most states. I use the word ‘culling’ because the measures announced by the WA Premier and the Minister for Fisheries amount to culling, through the use of a program of baited drums along targeted areas of the coast.

An important species

The counter argument to the debate is based around the conservation value of the white shark, as a threatened species, and as an apex predator.

Our fear of sharks, and particularly the white shark, reflects its success of the species as a ruthless predator. Such predators play a key role in our ecosystem, by keeping the population levels of their prey species at appropriate levels to help maintain stability in marine ecosystems. Removing these predators, known as a ‘top-down effect’, can change the balance, and have unknown or unpredictable consequences on those ecosystems. Because of this role, again, we need to be cautious about introducing a culling program.

Putting aside the argument that we should not be killing white sharks, it is highly debatable whether a culling program like the one proposed by the Western Australian Government will have any measurable effect on public safety. It assumes that the sharks will be attracted to the bait rather than being attracted through other sensory mechanisms to a person whom they mistake for their usual prey (for example, sea lions). Also, other marine species will almost certainly be caught by those hooks, creating a by-catch issue. The consequences of this, and the potential for by-catch to attract sharks into the area are unknown.

Instead of culling sharks, we should be looking at ways to reduce our encounters with these predators. The Department of Fisheries already has an acoustic tracking systems in place, but because there are few sharks that have had transmitting tags attached or inserted, this approach has limited value in detecting sharks entering waters near populated beaches.

There are also electronic devices and wetsuits that are marketed as deterring sharks or ‘hiding’ water users, though there is limited evidence that these work. We need to be placing more effort and funds into testing these devices and developing new technology that allows us to either deter sharks or reduce our encounters with them.

We also need to understand population size and preferred habitats of this species. Perhaps even more importantly, there needs to be targeted and informative education program to the public about the risks associated with entering the water. While the risk of being attacked is very small, the public can then make informed decisions about those risks.

ECU’s School of Natural Sciences.

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