Shark net

From Wikipedia, the free encyclopedia
Jump to: navigation, search
For other uses, see Shark net (disambiguation).
Simplified diagram of shark net in New South Wales, Australia

A shark net is a submerged net placed around beaches to reduce shark attacks on swimmers.

Shark nets do not offer complete protection but work on the principle of "fewer sharks, fewer attacks". They reduce occurrence via shark mortality. Reducing the local shark populations is believed to reduce the chance of an attack. The large mesh size of the nets is designed specifically to capture sharks and prevent their escape until eventually, they drown. Due to boating activity, the nets also float 4 metres or more below the surface and do not connect with the shoreline (excluding Hong Kong's shark barrier nets) thus allowing sharks the opportunity to swim over and around nets.

Bycatch[edit]

Shark nets also result in high incidence of bycatch, including threatened and endangered species like sea turtles, dugongs, dolphins and whales.[1] In QLD in the 2011/12 summer season there were 7000 sharks caught, 290 above 4 metres in shark nets and drum lines.[2]

Animal welfare groups suggest alternatives such as surf lifesaving patrols, public education on shark behaviour, radio signals, sonar technology and electric nets. Drum lines are also viewed, by some people, as an alternative: they consist of baited hooks aimed at catching only large sharks (though turtles, dolphins and rays are sometimes hooked).

Australia[edit]

Graph of sharks caught in Queensland's Shark Control Program (by type) July 1997- June 2014

In New South Wales, Australia, 51 beaches are netted.[3] 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 m. 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 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 70 years while the nets have been in operation, there has been only one fatal attack on a netted beach.[4]

In Queensland, Australia, drum lines are used in combination with shark nets. Queensland's Shark Control Program has been in place since the early 1960s. In Queensland's 2011/12 summer season there were 714 sharks caught, 281 above 2 metres in shark nets and drum lines.[5] Since 1997, the program catches 500-900 sharks annually, including several shark species of conservation concern. They include the following:

Common Name Scientific Name IUCN Redlist Status EPBC Conservation Listing (AUS)
Great hammerhead Sphyrna mokarran Endangered[6]
Great white shark Carcharodon carcharias Vulnerable[7] Vulnerable[8]
Grey nurse shark Carcharias taurus Vulnerable[9] Critically Endangered (East Coast) Population[8]
Scalloped hammerhead Sphyrna lewini Endangered[10]

A fatal attack in Queensland occurred in January 2006 at Amity Point on North Stradbroke Island. The water at this location drops off to 30 metres depth, and bull sharks are known to frequent the area.[11] Other beaches around the island were protected with drum lines at the time.[12]

Hong Kong[edit]

In Hong Kong, after three swimmers were killed by sharks in 1995, the government installed shark nets on gazetted beaches. Unlike the long-line and gill-net designs commonly used in Australia and South Africa, these are permanent installations and work as barrier nets. There have been zero fatalities since installation in 1995. As of 2014, shark nets are in place at 32 Hong Kong beaches.[13]

Barrier net design[edit]

The Hong Kong nets are generally 35 mm square on the surface 2 m and 100 mm square thereafter. They are suspended off 225 mm HDPE pipe or BL14 Marine Float Lines, and anchored strongly to resist the many typhoons and waves up to 10 m. They are anti-fouled, and spend an average of 9 months a year in the water. An average net enclosure would be 500 m long and either semi-circular or rectangular in shape. They are diver-inspected a minimum of two times a week, and independent verification is required. They also exclude floating refuse, and clearly define the swimming area. They can be clearly picked out on Google Earth - at 22^14'38" North, 114^11'26" East, see "Repulse Bay".[14]

South Africa[edit]

In South Africa, numerous beaches in KwaZulu-Natal province are protected by the KwaZulu-Natal Sharks Board.[15]

See also[edit]

References[edit]

  1. ^ [1][dead link]
  2. ^ "Data Tables: Shark control program: Sharks caught by area, Queensland, 2002–03 to 2012–13 (OESR, Queensland Treasury)". Oesr.qld.gov.au. 2013-07-26. Retrieved 2013-09-11. 
  3. ^ "Summer is coming and so are the sharks". Smh.com.au. 2012-10-19. Retrieved 2013-09-11. 
  4. ^ "NSW Shark Meshing publications | NSW Department of Primary Industries". Dpi.nsw.gov.au. Retrieved 2013-09-11. 
  5. ^ "Data Tables: Shark control program: Sharks caught by area, Queensland, 2002–03 to 2012–13 (OESR, Queensland Treasury)". Oesr.qld.gov.au. 2013-07-26. Retrieved 2013-09-11. 
  6. ^ "Sphyrna mokarran". The IUCN Red List of Threatened Species. International Union for the Conservation of Nature. Retrieved 2014-09-14. 
  7. ^ "Carcharodon carcharias". The IUCN Red List of Threatened Species. International Union for the Conservation of Nature. Retrieved 2014-09-14. 
  8. ^ a b "EPBC Act List of Threatened Fauna". Department of the Environment. Australian Government. 2014. Retrieved 2014-09-14. 
  9. ^ "Carcharias taurus". The IUCN Red List of Threatened Species. International Union for the Conservation of Nature. Retrieved 2014-09-14. 
  10. ^ "Sphyrna lewini". The IUCN Red List of Threatened Species. International Union for the Conservation of Nature. Retrieved 2014-09-14. 
  11. ^ "Woman killed in shark attack at Amity Point, Australia". WikiNews. 2006-01-08. Retrieved 2014-09-14. 
  12. ^ Sarah Vogler. "Monster shark spreads fear off Queensland coast". Couriermail.com.au. Retrieved 2013-09-16. 
  13. ^ "Safety at the beach". GovHK. 2014-08. Retrieved 2014-09-14.  Check date values in: |date= (help)
  14. ^ 76 Chung Hom Kok Rd (1970-01-01). "Google Maps". Google.com. Retrieved 2013-09-11. 
  15. ^ [2][dead link]

External links[edit]