Few creatures can evoke fear like great white sharks. The largest of all predatory fish help regulate marine food webs by patrolling the world’s tropical and subtropical waters, searching for fish, turtles, birds, and mammals. In coastal areas where cold water currents converge with equatorial systems, such as around Australia, South Africa, and California, adult great white sharks are particularly abundant, feeding on seal and sea lion populations that thrive in such seas; productive environments that also lure tourists. Exacerbated by the Jaws films of the 1970s, the fears generated by great white sharks have led to various measures to keep bathers safe, such as the installation of shark nets; yet these approaches impact other marine species and are not fully effective. New solutions, however, are being trialled in South Africa, which might offer a breakthrough.
Despite the proximity between sharks and humans, the number of shark attacks is surprisingly low: globally, around 100 shark attacks are reported each year, and between 1990 and 2011 there were 139 unprovoked great-white shark attacks, of which 29 were fatal (in comparison, an estimated 175,000 children die of drowning every year). In coastal regions that are popular with tourists and prone to shark attacks, shark nets are often installed to bring comfort to swimmers. These structures usually have a large mesh size to entangle and drown sharks and reduce the risk of attacks. Many shark nets are not connected to the shoreline and are positioned several metres below the water’s surface to enable boats – and thus sharks – to pass over and around. Shark nets do not offer total protection: rather, they lower the number of sharks in an area by increasing shark mortality and deterring territory establishment.
In eastern Australia, extensive nets up to 500 metres from the shore are serviced every 24 to 48 hours to remove debris and dead marine life. These nets were first established in the late-1930s, and only one fatal attack has occurred within a netted area since installation. Although the Australian nets are now fitted with acoustic devices to deter whales and dolphins, they – and other nets around the world – do not only target predatory sharks; harmless shark species and other large fish, turtles, manatees and other mammals can also become entwined. Conservationists have suggested alternative approaches, including radio signals, sonar technology, electric nets and drum-lines (baited hooks designed to catch large sharks), yet these measures are not always effective.
A drowned Zambezi shark entangled in a traditional shark net off Durban, South Africa
South African Advancements
The western coast of South Africa is bathed by the Benguela Current, which delivers nutrient-rich waters from the Antarctic. These conditions support an abundance of marine life, which attracts both sharks and tourists. Over the last decade there have been five fatal great-white shark attacks in South African waters; concerns that these incidents will impact future tourism has led to the development of an $80,000 experiment to implement protective shark nets that do not threaten marine species.
The inshore waters around Durban, on the east coast of South Africa, support anchored gill-nets that kill some 600 sharks and many other marine animals each year. In Cape Town, however, new custom-designed shark nets are being established that act as a barrier, not a trap. Trialled around the town of Fish Hoek, where a swimmer was seriously injured during a shark attack in 2011, the new nets are similar to those used in Hong Kong and the Seychelles, but will be removed at night. Extending from the water’s surface to the seabed, these fine-meshed nets are expected to prevent animals from entangling and drowning, and also stop sharks from entering swimming zones. Although expensive, such measures are viewed as the best approach for safeguarding sharks, protecting humans, and stimulating the tourism industry, which in South Africa generates $2.2 billion each year.
The new nets should help conserve sharks (and other marine organisms) around South Africa while enabling the tourism sector to grow. This is important: as apex carnivores, predatory sharks help control the populations of other marine species at higher trophic levels. There are a number of threats that are impacting shark communities, including pollution, overfishing, habitat destruction, hunting, and shark-finning. Great-white sharks, which have a gestation period of eleven months and take over a decade to reach sexual maturity, are now considered a vulnerable species due to hunting and fishing – often as a result of human fear and ignorance. According to the International Shark Attack File, there have been 2,569 confirmed, unprovoked shark attacks around the world between 1580 and 2011, of which 484 were fatal. In comparison, an estimated 38 million sharks are killed each year for the shark finning trade. Of the 360 species of shark, only great-white, tiger, and bull sharks are known to have caused more than ten fatal attacks on humans per species. There is also a growing interest in shark tourism and especially shark diving, suggesting the value of a live shark is greater than that of its dead counterpart.
As top carnivores, it is of great importance that large predatory sharks are protected to balance the ecology of marine food-webs. Hopefully, the new South African nets will allow such fish to continue living in waters that are popular with humans, especially considering the uncertain futures that many shark species face.