Жағалаудағы қауіпсіздік: Жүзгіштерді акулалардан қорғау үшін су асты торлары

A submerged barrier that protects swimmers from shark attacks

A shark net is a submerged section of gillnets placed at beaches designed to intercept large marine animals including sharks, with the aim to reduce the likelihood of shark attacks on swimmers. Shark nets used are gillnets which is a wall of netting that hangs in the water and captures the marine animals by entanglement, however only around 10% of catch is the intended target shark species. The nets in Queensland, Australia, are typically 186m long, set at a depth of 6m, have a mesh size of 500mm and are designed to catch sharks longer than 2m in length. The nets in New South Wales, Australia, are typically 150m long, set on the sea floor, extending approximately 6m up the water column, are designed to catch sharks longer than 2m in length. Shark nets do not create an exclusion zone between sharks and humans, and 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 aim to reduce occurrence via shark mortality. Shark nets such as those in New South Wales are designed to entangle and capture sharks that pass near them. 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. They also argue there is no science showing that nets make the ocean safer for people. Nets were first deployed off certain beaches in KwaZulu Natal (formerly Natal), South Africa, in 1952. Shark nets were also used off Dunedin, New Zealand for roughly 40 years, and were removed in 2011. The nets were found to be detrimental to the environment; 700 non target species were killed. No shark attacks have occurred since their removal. As of 2018, shark nets are used in New South Wales, Queensland and KwaZulu Natal. 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.

Ongoing shark control programs have been very successful in reducing the incidence of shark attack at the protected beaches. In Queensland in the 2011/12 summer season there were 700 sharks caught, 290 above 4 metres in shark nets and drum lines. 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. Use of the pingers has been shown to significantly reduce marine mammal bycatch. The current net program in New South Wales has been described as being "extremely destructive" to marine life. Between September 2017 and April 2018, more than 403 animals perished 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. However bycatch from shark nets is minor compared to bycatch from other activities. On average 15 Great white sharks are caught by the NSW and Queensland shark control programme each year, compared to 186 caught in Australia from other activities. Australia's commercial shark fishing industry is catching over 1200 tonne of shark each year, Tuna and swordfish longline fishing off the coast of South Africa reported 39,000 to 43,000 sharks died each year between 1995 and 2005.

In South Africa, shark nets are installed at numerous beaches in KwaZulu Natal by the KwaZulu Natal Sharks Board. Shark nets have been installed in KwaZulu Natal since the 1950s However more than 33,000 sharks have perished in KwaZulu Natal's nets in a 30 year period. KwaZulu Natal's shark net program has been called "archaic" and "disastrous to the ecosystem".