Shark net

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 are not to be confused with shark barriers.

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. Historical shark attack figures suggest that the use of shark nets and drumlines does markedly reduce the incidence of shark attack when implemented on a regular and consistent basis.[1] 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. Shark nets can cost up to 1.4 million dollars.

History

Shark net meshing was thought up by the NSW Fisheries in 1936, after a decade and a half of relentless Shark attacks off Sydney beaches. In March 1935, for example, two people — one at North Narrabeen and one at Maroubra — were killed by great white sharks in a single week. The meshing was never designed to enclose a piece of water — even back then, they knew barrier nets would never survive a surf zone. Instead, it was designed to catch large dangerous sharks as they swam within range of the surf. At first, the catch was huge; over 600 sharks in the first year of operation, off just a few Sydney beaches. But over time, even without adjusting for the spread of the program across almost all Sydney beaches and into Wollongong and Newcastle, the catch declined. Today's NSW meshing annual average catch is 143 sharks, quite a number of which are released alive.[2]

Nets were also first deployed off certain beaches off KwaZulu-Natal (KZN, formerly Natal) South Africa, in 1952.[3]

Effectiveness of Shark Control

Ongoing shark control programs have been very successful in reducing the incidence of shark attack at the protected beaches.[3] In the years from 1900 to 1937, 13 people were killed off NSW surf beaches by sharks; over the next 72 years, the death rate fell to eight, only one of which was at a meshed beach. This in a period when the NSW human population rose from 1.4 million to seven million — and when way more people began going to the beach.[2]

In Queensland, there has been only one fatal attack on a controlled beach since 1962, compared to 27 fatal attacks between 1919 and 1961.Statistics from the NSW Department of Primary Industries indicate that before nets were introduced in NSW in 1936 there was an average of one fatal shark attack every year. There has been only one fatal attack on a protected beach since then and that was in 1951. Similarly, between 1943 and 1951 the South African city of Durban experienced seven fatal attacks but there have been none since nets were introduced in 1952. A more recent comparison shows that in South Africa there were three shark attacks, none fatal, at protected beaches in KwaZulu-Natal between 1990 and 2011, while there were 20 fatal attacks in the same period at unprotected beaches in the Eastern and Western Cape Provinces.[1]

Bycatch

Shark nets also result in incidence of bycatch, including threatened and endangered species like sea turtles, dugongs, dolphins and whales.[4] In QLD in the 2011/12 summer season there were 700 sharks caught, 290 above 4 metres in shark nets and drum lines.[5]

In NSW, the meshing averages one humpback whale every two years; the whale is almost always released alive. In Queensland in 2015, the bycatch included one bottlenose and seven common dolphin (one released alive), 11 catfish, eight cow-nose rays, nine eagle rays, 13 loggerhead turtles, five manta rays (all but one survived), eight shovelnose rays, three toadfish, four tuna, and a white spotted eagle, which was safely released.[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).

However, it should be noted that bycatch from shark nets is minor compared to bycatch from other activities. For example, Australia's commercial shark fishing industry is taking over 1200 tonne of shark out of our various fisheries each year: everything from gummy shark to mako, and very likely a few white sharks as well. The NSW prawn trawling industry alone results in 64 tonne of shark as bycatch each year. Six percent of what's caught in the tuna longline fisheries in northern Australia is shark.[2]

Australia

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.[6] 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.[7]

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.[8] 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[9]
Great white shark Carcharodon carcharias Vulnerable[10] Vulnerable[11]
Grey nurse shark Carcharias taurus Vulnerable[12] Critically Endangered (East Coast) Population[11]
Scalloped hammerhead Sphyrna lewini Endangered[13]

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.[14] Other beaches around the island were protected with drum lines at the time.[15]

Hong Kong

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.[16]

Shark enclosures are not used more widely because they usually disintegrate in surf beaches, and so are normally constructed only around sheltered areas such as harbour beaches. It should be noted that where there are surf conditions at Hong Kong beaches, the swell is "typically small". Even if they were in place at surf beaches, they would not protect surfers who go some distance from shore.[17]

Barrier net design

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".[18]

South Africa

In South Africa, numerous beaches in KwaZulu-Natal province are protected by the KwaZulu-Natal Sharks Board.[19]

See also

References

  1. 1 2 http://www.abc.net.au/news/2013-12-22/can-governments-protect-people-from-killer-sharks/5158880
  2. 1 2 3 4 http://www.theherald.com.au/story/4275374/beyond-the-panic-the-facts-about-shark-nets/
  3. 1 2 Curtis; et al. "Responding to the risk of white shark attack: updated statistics, prevention, control, methods and recommendation. Chapter 29 In: M. L. Domeier (ed). Global Perspectives on the Biology and Life History of the White Shark" (PDF). CRC Press. Boca Raton, FL. Retrieved 22 November 2016.
  4. ↑ Archived March 22, 2005, at the Wayback Machine.
  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. ↑ "Summer is coming and so are the sharks". Smh.com.au. 2012-10-19. Retrieved 2013-09-11.
  7. ↑ "NSW Shark Meshing publications | NSW Department of Primary Industries". Dpi.nsw.gov.au. Retrieved 2013-09-11.
  8. ↑ "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.
  9. ↑ "Sphyrna mokarran". The IUCN Red List of Threatened Species. International Union for the Conservation of Nature. Retrieved 2014-09-14.
  10. ↑ "Carcharodon carcharias". The IUCN Red List of Threatened Species. International Union for the Conservation of Nature. Retrieved 2014-09-14.
  11. 1 2 "EPBC Act List of Threatened Fauna". Department of the Environment. Australian Government. 2014. Retrieved 2014-09-14.
  12. ↑ "Carcharias taurus". The IUCN Red List of Threatened Species. International Union for the Conservation of Nature. Retrieved 2014-09-14.
  13. ↑ "Sphyrna lewini". The IUCN Red List of Threatened Species. International Union for the Conservation of Nature. Retrieved 2014-09-14.
  14. ↑ Wikinews:Woman killed in shark attack at Amity Point, Australia
  15. ↑ Sarah Vogler. "Monster shark spreads fear off Queensland coast". Couriermail.com.au. Retrieved 2013-09-16.
  16. ↑ "Safety at the beach". GovHK. Aug 2014. Retrieved 2014-09-14.
  17. ↑ http://www.abc.net.au/news/2013-12-22/fact-file-protecting-people-from-shark-attacks/5164882
  18. ↑ 76 Chung Hom Kok Rd (1970-01-01). "Google Maps". Google.com. Retrieved 2013-09-11.
  19. ↑ Archived March 31, 2009, at the Wayback Machine.
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