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Keeping our sharks....at a distance


In the last three years there have been six fatal shark attacks on popular beaches in Western Australia. In response, the state government announced on 10 December 2013 a program to catch large sharks (great white, bull and tiger) near heavily used beaches off Perth and the state’s South West (from Capel to Margaret River). The government program deploys baited drum lines one kilometre offshore, but this has been opposed by conservation groups because of the incidental catch of non-target species and the fact that the great white shark is a threatened species.

According to the Australian Shark Attack File, there have been 217 fatal recorded shark attacks in Australia since 1791. Most occurred in NSW and Queensland. Shark control programs using mesh nets were introduced in these two states over fifty years ago.

Although nets can reduce attacks, they are not ideal. They catch some sharks (thereby reducing numbers in an area), but do not provide a complete barrier. The problem is that many non-target sharks are caught too, along with rays, turtles and dolphins. (Recently, acoustic alarms added to NSW mesh nets have reduced the catch of dolphins by a third.) Green turtles tend to be caught more in nets while loggerhead turtles tend to caught by drum lines.

In NSW, shark meshing has been used since 1937 off 51 beaches between Newcastle and Wollongong. There have been 23 attacks and one fatality recorded off meshed beaches in NSW in that time. Large sharks caught in the mesh nets used to be killed but are now released, along with the captured non-target species (if they are still alive). In 1962 Queensland introduced its Shark Control Program using a combination of mesh nets and baited drum lines year round off 37 beaches from Cairns to the Gold Coast. All great white sharks captured in the nets are killed.

By contrast with NSW and its low level of fatal attacks off meshed beaches, six of the last eight Australian shark fatalities have been in WA. The great white shark is the principal species implicated in the WA attacks. A 2012 study of potential risk factors for great white shark attacks reported that most attacks in WA occur more than one kilometre offshore, with 44% of attacks occurring on scuba divers and snorkelers, and 37% on surfers and sea kayakers. Spring and winter were the commonest time for attacks; there were fewer attacks in water warmer than 22°C. The number of attacks by great whites, while still low, has increased faster than human population growth over the past twenty years. Another 2012 study, which examined the introduction of shark capture options in WA, questioned the effectiveness of shark meshing for preventing great white attacks, and of drum lines for reducing bull shark attacks. The study recommended against their use due to the high by-catch.

Some conservation groups oppose the WA government plan because the great white shark is itself a threatened species. Greens Senator Rachel Siewert called on Minister for the Environment Greg Hunt to examine the proposal under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC).

The great white shark, although long-lived, has a low reproductive rate. This makes the species less able to recover from being harvested. It is listed as Vulnerable under the EPBC Act. There are no reliable population estimates of great white sharks in Australian waters due to their scarcity and the migratory movements. However, the 2013 Recovery Plan claimed there has been no substantial recovery in the number of great whites. The two principal threats to the species are illegal and accidental catch by commercial and recreational fishers, and mortality related to the shark control programs in NSW and Queensland.

Great white sharks are capable of travelling long distances, such as between Australia and South Africa. They are not territorial animals, but they maintain distinct populations centred around Australia, New Zealand and South Africa. There are two genetically distinct populations in Australian waters, one off the east coast and the other off the south-western coast. Great white shark captures per unit effort by shark control programs have decreased over time, but it is unclear whether this reflects a localised reduction in shark numbers or an overall reduction in the eastern Australian population.

While a permit is normally required to take or kill threatened species such as the great white, the WA Government sought an exemption in the national interest under section 158 of the EPBC Act on 6 January 2014. The Minister, Greg Hunt, granted this exemption for the setting of 72 drumlines until 30 April 2014. He decided that public safety is a matter of national interest and that non-lethal methods to protect bathers from shark attacks are not yet proven to work in large areas.

 

 

 

Tags: environment