Engineering:Shark net

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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. The majority of Shark nets used are Gillnets which is a wall of netting that hangs in the water and captures the targeted sharks by entanglement.[1] The nets in Queensland, Australia, are typically 186m long, set at a depth of 6 m, have a mesh size of 500 mm and are designed to catch sharks longer than 2m in length.[2] 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. Shark nets such as those in New South Wales are designed to entangle and kill sharks and other animals that pass near them.[3] 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.[4] 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 A$1 million or A$20,000 per beach per year.[5]

Shark nets have been criticized by environmentalists, conservationists and animal rights activists — they say shark nets are unethical and harm the marine ecosystem.[6][7][3][8][9][10][11][12][13][14] They also say there is no science showing that nets make the ocean safer for people.[3] Christopher Neff, a Ph.D. scholar at the University of Sydney notes, "Internationally, shark nets have been labeled a 'key threatening process' for killing endangered species." He adds: " ... killing endangered species to boost public confidence or to show government action is not workable. It is a disservice to the public."[6] Jessica Morris of Humane Society International calls shark nets a "knee-jerk reaction" and says, "sharks are top order predators that play an important role in the functioning of marine ecosystems. We need them for healthy oceans."[8]


History

Shark net meshing was thought up by the New South Wales Fisheries in 1935, 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 New South Wales meshing annual average catch is 143 sharks, quite a number of which are released alive.[15]

Nets were also first deployed off certain beaches off KwaZulu-Natal (KZN, formerly Natal) South Africa, in 1952.[16]

As of 2018, shark nets are currently used in New South Wales, Queensland and KwaZulu-Natal.[10][17][18] In August 2018, it was announced that the nets in northern New South Wales would be removed, but that the nets in Sydney, Newcastle and Wollongong would stay.[7][19] The New South Wales Green party said they wanted all lethal nets to be removed.[19]

Effectiveness of shark nets

Ongoing shark control programs have been somewhat successful in reducing the incidence of shark attack at the protected beaches.[16][20] In the years from 1900 to 1937, 13 people were killed off New South Wales 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 New South Wales human population rose from 1.4 million to seven million — and when more people began going to the beach.[15]

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 New South Wales Department of Primary Industries indicate that before nets were introduced in New South Wales 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.[4]

However, the net program in New South Wales has been called "outdated and ineffective".[7] It has been argued that shark nets do not protect swimmers.[3] 65% of shark attacks in New South Wales occurred at netted beaches.[8]

Environmental impact

Shark nets result in incidence of bycatch, including threatened and endangered species like sea turtles, dugongs, dolphins and whales.[21] In Queensland in the 2011/12 summer season there were 700 sharks caught, 290 above 4 metres in shark nets and drum lines.[22]

In New South Wales, 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.[15]

New South Wales and Queensland also utilize acoustic pingers attached to the nets to reduce bycatch of dolphins, whales and other marine mammals.[23] Use of the pingers has been shown to significantly reduce marine mammal bycatch.[24]

The current net program in New South Wales has been described as being "extremely destructive" to marine life.[25] Between September 2017 and April 2018, more than 403 animals were killed in the nets in New South Wales, including 10 critically-endangered grey nurse sharks, 7 dolphins, 7 green sea turtles and 14 great white sharks.[7] Between 1950 and 2008, 352 tiger sharks and 577 great white sharks were killed in the nets in New South Wales — also during this period, a total of 15,135 marine animals were killed in the nets.[10] More than 5,000 marine turtles have been caught on the nets.[8] The New South Wales government prohibits people from rescuing entangled animals — this prohibition has been called "heartless and cruel".[9]

In a 30-year period, more than 33,000 sharks have been killed in KwaZulu-Natal's shark net program.[18] During the same 30-year period, 2,211 turtles, 8,448 rays, and 2,310 dolphins were killed in KwaZulu-Natal's shark net program.[18]

Animal welfare groups suggest alternatives such as surf lifesaving patrols, public education on shark behaviour, radio signals, sonar technology and electric nets.

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.[15]

Cost

Total cost for the Shark netting program in NSW for the 2009/10 year was approximately AUD 1m, which included the cost of the nets, contractors, observers and shark technician, shark meshing equipment (dolphin pingers and whale alarms etc.), and compliance audit activities.[5] For the 51 beaches protected,[5] this represents a financial cost of approximately AUD$20,000 per beach per year.

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.[26] 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.[27] From 1950 to 2008, hundreds of great white sharks and tiger sharks were killed in the nets in New South Wales.[10]

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.[22] Since 1997, the program kills 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[28]
Great white shark Carcharodon carcharias Vulnerable[29] Vulnerable[30]
Grey nurse shark Carcharias taurus Vulnerable[31] Critically Endangered (East Coast) Population[30]
Scalloped hammerhead Sphyrna lewini Endangered[32]

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.[33] Drum lines were installed at beaches around the island at the time.[34]

South Africa

In South Africa , shark nets are installed at numerous beaches in KwaZulu-Natal by the KwaZulu-Natal Sharks Board.[35] Shark nets have been installed in KwaZulu-Natal since the 1950s.[18] More than 30,000 sharks have been killed in KwaZulu-Natal's nets.[18] KwaZulu-Natal's shark net program has been called "archaic".[18]

See also

  • Drum line
  • Shark attack prevention
  • Shark Shield
  • Shark proof cage
  • Shark culling

References

  1. ↑ Fisheries, NOAA. "Gillnets: Fishing Gear and Risks to Protected Species :: NOAA Fisheries". http://www.nmfs.noaa.gov/pr/interactions/gear/gillnet.htm. Retrieved 22 April 2017. 
  2. ↑ "Shark control equipment and locations". https://www.daf.qld.gov.au/fisheries/services/shark-control-program/shark-control-equipment-and-locations. Retrieved 22 April 2017. 
  3. ↑ 3.0 3.1 3.2 3.3 Forrest, Alice. http://www.sealifetrust.org.au/news/latest/shark-nets-australia-work "Shark Nets in Australia – What Are They and How Do They Work?". sealifetrust.org. Retrieved October 17, 2018.
  4. ↑ 4.0 4.1 "Can governments protect people from killer sharks?". 22 December 2013. http://www.abc.net.au/news/2013-12-22/can-governments-protect-people-from-killer-sharks/5158880. Retrieved 22 April 2017. 
  5. ↑ 5.0 5.1 5.2 Green, M., Ganassin, C. and Reid, D. D.. "Report into the NSW Shark Meshing (Bather Protection) Program". State of New South Wales through NSW Department of Primary Industries. http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0015/623400/Report-into-the-NSW-Shark-Meshing-Program.pdf. Retrieved 21 December 2016. 
  6. ↑ 6.0 6.1 Pepin-Neff, Christopher. https://theconversation.com/the-untold-story-of-shark-nets-in-australia-3748 "The Untold Story of Shark Nets in Australia". theconversation.com. Retrieved October 17, 2018.
  7. ↑ 7.0 7.1 7.2 7.3 Mackenzie, Bruce (August 4, 2018). http://www.swellnet.com/news/swellnet-dispatch/2018/08/04/sydney-shark-nets-set-stay-despite-drumline-success "Sydney Shark Nets Set to Stay Despite Drumline Success". swellnet.com. Retrieved October 17, 2018.
  8. ↑ 8.0 8.1 8.2 8.3 Morris, Jessica (December 8, 2016). https://hsi.org.au/blog/2016/12/08/shark-nets-death-traps-for-marine-animals/ "Shark Nets – Death Traps For Marine Animals". hsi.org.au. Retrieved October 17, 2018.
  9. ↑ 9.0 9.1 Eddie, Rachel (January 9, 2018). https://thenewdaily.com.au/news/state/nsw/2018/01/09/greens-shark-nets-rays/ "Threat to Cut Shark Nets if Government Fails to Act". thenewdaily.com. Retrieved October 17, 2018.
  10. ↑ 10.0 10.1 10.2 10.3 https://www.marineconservation.org.au/pages/shark-culling.html "Shark Culling". marineconservation.org.au. Retrieved October 17, 2018.
  11. ↑ http://www.ausmarinescience.com/marine-science-basics/marine-biology/sharks/ "Sharks - Marine Science Australia". Ausmarinescience.com. Archived from the original on 2018-07-27. Retrieved October 17, 2018.
  12. ↑ http://www.seashepherd.org.au/apex-harmony/overview/queensland.html "Queensland - Overview". Seashepherd.org.au. Retrieved October 17, 2018.
  13. ↑ http://theconversation.com/western-australias-shark-culls-lack-bite-and-science-21371 "Western Australia's Shark Culls Lack Bite (And Science)". Meyer, Carl (December 11, 2013). theconversation.com. Retrieved October 17, 2018.
  14. ↑ Schetzer, Alana. http://pursuit.unimelb.edu.au/articles/sharks-how-a-cull-could-ruin-an-ecosystem "Sharks: How a cull could ruin an ecosystem". puruit.unimelb.edu.au. Retrieved October 17, 2018.
  15. ↑ 15.0 15.1 15.2 15.3 Media, Australian Community Media - Fairfax (8 November 2016). "Beyond the panic: the facts about shark nets". http://www.theherald.com.au/story/4275374/beyond-the-panic-the-facts-about-shark-nets/. Retrieved 22 April 2017. 
  16. ↑ 16.0 16.1 Curtis et al (2012). "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". CRC Press. Boca Raton, FL.. http://biotelemetry.ucdavis.edu/publications/12_Curtis%20et%20al_Global%20Perspectives_Risk%20of%20Shark%20Attack_2011.pdf. Retrieved 22 November 2016. 
  17. ↑ https://www.seashepherd.org.au/apex-harmony/overview/about-the-campaign.html "About the Campaign: Sea Shepherd Working Together With The Community To Establish Sustainable Solutions To Shark Bite Incidents". seashepherd.org.au. Retrieved October 17, 2018.
  18. ↑ 18.0 18.1 18.2 18.3 18.4 18.5 http://www.sharkangels.org/index.php/media/news/157-shark-nets "Shark Nets". sharkangels.org. Retrieved October 17, 2018.
  19. ↑ 19.0 19.1 https://www.theguardian.com/environment/2018/aug/17/shark-nets-to-be-removed-from-all-nsw-north-coast-beaches "Shark Nets To Be Removed From All NSW North Coast Beaches". August 17, 2018. Archived from the original on 2018-09-05. Retrieved September 28, 2018.
  20. ↑ Dudley, S.F.J. (1997). "A comparison of the shark control programs of New South Wales and Queensland (Australia) and KwaZulu-Natal (South Africa)". Ocean Coast Manag (34): 1–27. https://www.researchgate.net/publication/223563025_A_comparison_of_the_shark_control_programs_of_New_South_Wales_and_Queensland_Australia_and_KwaZulu-Natal_South_Africa. 
  21. ↑ [1]
  22. ↑ 22.0 22.1 "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. http://www.oesr.qld.gov.au/products/tables/shark-control-program-caught-area/index.php. Retrieved 2013-09-11. 
  23. ↑ "Subscribe - theaustralian". http://www.theaustralian.com.au/national-affairs/state-politics/shark-net-pings-saving-dolphins-turtles/news-story/6894e4520eea546eaed5efde29e4460a. Retrieved 22 April 2017. 
  24. ↑ Jay Barlow, Grant A. Cameron. "FIELD EXPERIMENTS SHOW THAT ACOUSTIC PINGERS REDUCE MARINE MAMMAL BYCATCH IN THE CALIFORNIA DRIFT GILL NET FISHERY". Marine Mammal Science 19: 265–283. doi:10.1111/j.1748-7692.2003.tb01108.x. http://onlinelibrary.wiley.com/doi/10.1111/j.1748-7692.2003.tb01108.x/abstract. Retrieved 31 December 2016. 
  25. ↑ https://www.buzzfeed.com/elfyscott/heres-what-you-need-to-know-about-australias-smart-drum?utm_term=.qcNzkX738#.xlDVyOnW7 Here's What You Need To Know About Australia's SMART Drum Lines Being Used To Prevent Shark Attacks. Elfy Scott. July 5, 2018. Retrieved October 17, 2018.
  26. ↑ "Summer is coming and so are the sharks". Smh.com.au. 2012-10-19. http://www.smh.com.au/environment/animals/summer-is-coming-and-so-are-the-sharks-20121018-27tx4.html. Retrieved 2013-09-11. 
  27. ↑ "NSW Shark Meshing publications | NSW Department of Primary Industries". Dpi.nsw.gov.au. http://www.dpi.nsw.gov.au/fisheries/info/sharksmart/meshing. Retrieved 2013-09-11. 
  28. ↑ "Sphyrna mokarran". International Union for the Conservation of Nature. http://www.iucnredlist.org/details/39386/0. Retrieved 2014-09-14. 
  29. ↑ "Carcharodon carcharias". International Union for the Conservation of Nature. http://www.iucnredlist.org/details/3855/0. Retrieved 2014-09-14. 
  30. ↑ 30.0 30.1 "EPBC Act List of Threatened Fauna". Australian Government. 2014. http://www.environment.gov.au/cgi-bin/sprat/public/publicthreatenedlist.pl?wanted=fauna. Retrieved 2014-09-14. 
  31. ↑ "Carcharias taurus". International Union for the Conservation of Nature. http://www.iucnredlist.org/details/3854/0. Retrieved 2014-09-14. 
  32. ↑ "Sphyrna lewini". International Union for the Conservation of Nature. http://www.iucnredlist.org/details/39385/0. Retrieved 2014-09-14. 
  33. ↑ Wikinews:Woman killed in shark attack at Amity Point, Australia
  34. ↑ Sarah Vogler. "Monster shark spreads fear off Queensland coast". Couriermail.com.au. http://www.couriermail.com.au/news/queensland/monster-shark-spreads-fear-off-queensland-coast/story-e6freoof-1225790886188. Retrieved 2013-09-16. 
  35. ↑ [2]

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