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Background information
[Most of the information contained in this background note has been drawn from the Wikipedia 'Shark net' entry (accessed at http://en.wikipedia.org/wiki/Shark_net and the 2006 Queensland Government Department of Primary Industries and Fisheries 'Report on the Queensland Shark Safety Program' (accessed at http://en.wikipedia.org/wiki/Shark_net)http://www2.dpi.qld.gov.au/extra/pdf/fishweb/sharksafetyreport.pdf)]
Shark control measures in Australia
There is a variety of shark control measures employed in different Australian states.
New South Wales
In New South Wales, 51 beaches are netted. The nets are maintained by the New South Wales Department of Primary Industries. The nets are generally 150 metres long, 6 m wide and 'bottom-set' on the seabed in depths of 10 metres. The nets can be 500 metres from the beach. The mesh is sized 50-60 centimetres. Nets are lifted every 24 to 48 hours for servicing so as to prevent rotting, to clean out debris and to remove dead sharks and other marine life. It is said that 35-50% of the sharks are entangled from the beach side. Acoustic 'pingers' have been fitted to the nets to warn off dolphins and whales and the nets are not in place in winter, the whale migration season.
The Department of Primary Industries states that the nets have 'never been regarded as a means of absolutely preventing any attacks', but help to deter sharks from establishing territories. The netting program began in 1937 and during the 70 year period during which the nets have been in operation, there has been only one fatal attack on a netted beach.
Queensland
In Queensland a 'Shark Safety Program' (SSP) has been in place on beaches since 1962. It relies on nets, drum lines or a combination of both to remove high risk sharks from a particular location.
In the 44 year history of the program, there has been one fatal attack on a beach with SSP measures in place. That occurred in January 2006.
The program was initially restricted to the Gold and Sunshine Coasts. Requests from local governments, however, led to inclusion in the program of other beaches throughout the state, and minor extensions to the program occurred up to 1996.
Beaches with shark control equipment installed tend to be close to high human population densities where the chance of shark-human interaction is highest.
Nets are 186 metres in length. Each net is made up of 3 x 62 metre sections. The nets have a depth of 6 metres and a mesh size of 500 millimetres. They are marked with inflatable buoys and are anchored to the seabed using high-holding anchors.
The nets are set adjacent to and generally parallel to the shoreline according to the prevailing tides and currents. Their distance from shore is determined by topographical and sea conditions/feature of each area. Equipment is usually placed far enough offshore to preclude bather interaction.
For the drum line method, a 14/0 shark hook is suspended from an inflatable buoy using a 5 or 6 millimetre galvanised chain trace two metres long. The depth of the hook is adjusted to suit local conditions. The hook generally is baited every other day with fresh sea mullet, which is a naturally occurring food source for sharks. Each drum line is anchored to the seabed using varying lengths of 12 millimetre polypropylene rope and a high-holding anchor. The fresh bait attracts sharks and the float provides high impact resistance to set the hook if the bait is taken. Equipment is serviced by independent contractors who work under Queensland Boating and Fisheries Patrol (QBFP) supervision. The program operates at 10 Queensland centres and gear is present on 84 beaches.
In both New South Wales and Queensland there have been fatalities at non-protected beaches; however, there have been severe shark attacks on beaches that are protected by nets.
South Australia and Victoria
South Australia and Victoria have no direct and active anti-shark measures however South Australia conducts over-flights of beaches and maintains a data base of shark sightings.
Western Australia
Prior to the recent Barnett Government announcement, Western Australia had no specific shark catching equipment in place; however, there is a system of aerial surveillance at selected locations from October to February. This is used to alert authorities to the presence of dangerous sharks near beaches
Under the system about to be imposed, drumlins will be set up at eight populous beaches. The metropolitan Perth beaches where the devices will be set are: Ocean Reef/Mullaloo, Trigg/Scarborough, Floreat/City Beach, Cottesloe/North Cottesloe and Port Leighton. In the South West region, drum lines will be set at Old Dunsborough, Meelup/Castle Rock and Gracetown - where the most recent fatality occurred - up until the end of school holidays in February. Thereafter, surfing hotspots south of Cape Naturaliste will be the focus.
Any white shark, tiger shark or bull shark greater than 3m total length caught on the drum-lines will be 'humanely destroyed'. Current directions on the humane destruction of large sharks 'involve the use of a firearm'. Any sharks that are dead or destroyed will be tagged and taken offshore (distance to be confirmed) and discarded;
All other animals taken on the drum lines will be released alive 'where possible'. Any animals which are dead, or considered not in a condition to survive, are to be humanely destroyed, tagged and taken offshore for disposal.
The drum lines will be patrolled for 12 hours each day, between 6am and 6pm, seven days a week. Drum lines will be baited at both the commencement of, and prior to the end of, each patrol day, while all used baits will be disposed onshore. Exemptions from 'various state legislation' which prohibit the take, or attempted take, of protected shark species will be provided.
It is likely a 50m exclusion zone will be implemented around each drum line. Only vessels operated by the contractor employed to clear the drum-lines will be allowed within the exclusion zone. The successful firm will also respond to shark threats, including the deployment of additional drum lines within 30 minutes.
The Western Australian government has called for professional shark fishermen (apparently those who will also check the drum-lines) to apply to patrol the state's waters and kill any shark bigger than three metres spotted in the designated zones.
Kill rate
The ABC's Fact Check site has stated, 'Contrary to common misconception, nets and drum-lines are not meant to be protective barriers for swimmers. They are meant to kill dangerous sharks.'
However, efforts are made in both Queensland and New South Wales to release sharks if they do not pose a threat to people, although the reality is that most sharks that encounter the devices do not survive. In Queensland, if a captured shark is found alive when the nets and drum-lines are cleared, it will be euthanised if dangerous or released alive where possible, if not.
In the first 11 months of 2013, 633 sharks were captured as part of the Queensland program, of which 297 were considered dangerous. Of the sharks captured 481 sharks died in shark control equipment, 122 were humanely killed following capture as they were considered dangerous, and 30 were released alive as they were considered non-dangerous. Thus, of the 633 sharks caught in nets, less than 5 per cent survived and were released.
In New South Wales during the 2011-12 program, 158 sharks were found entangled in nets, 5 per cent of which (56 sharks) were found alive and then released.
In Queensland, it has been noted that Hammerhead sharks and rays were particularly vulnerable to net capture, whereas higher catch rates of tiger sharks were observed for drum-lines. Nets caught more marine mammals, whereas drum-lines exhibited higher catch rates of the threatened loggerhead turtle. Survival was lower in nets than drum-lines.
By-catch species (turtles and marine mammals) were able to swim to the surface to breathe when they were hooked on drum-lines, enhancing their survival potential.