Shark Nets, Drumlines, and Safe Swimming
Most of the shark nets deployed by the KZNSB are 214 m long and 6 m deep and are secured at each end by two 35 kg anchors; all have a stretched mesh of 51 cm. The nets are laid in two parallel rows approximately 400 m offshore and in water depths of 10-14 m. A drumline consists of a large, anchored float (which was originally a drum) from which a single baited hook is suspended. Most beaches are protected either by two nets or by one net and four drumlines, but the quantity of gear varies from beach to beach. Durban, the largest coastal city and holiday resort in South Africa, has 17 nets, each 305 m in length, which cover all the popular swimming beaches between the mouth of the Umgeni River and the harbour entrance.
The KZNSB boat crews service the nets, every Monday through Friday, weather permitting. Only four of the 15 skiboats operate from harbours, with three boats based at Durban harbour and the forth at Richards Bay. All the other craft have to launch though the often heavy surf to reach the nets.
How do nets and drumlines work?
Shark nets do not form a complete barrier and sharks can swim over, under or around the ends of the nets. Neither, of course, do drumlines form a physical barrier. Both types of equipment function by reducing shark numbers in the vicinity of protected beaches, thereby lowering the probability of encounters between sharks and people at those beaches. The nets may have a limited barrier effect as well, but the fact that about one-third of the catch is caught on the shoreward side of the nets is evidence that such an effect is only partial. Drumlines are a recent introduction on the KwaZulu-Natal coast but their successful use in Queensland, Australia, indicates that the fishing effect of the protective equipment is of primary importance.
Are nets and drumlines fail-safe?
It was recognised before shark netting was introduced to the beaches of Sydney, Australia, in 1937 that only a complete enclosure would provide complete protection from shark attacks. Despite this, the safety record of shark nets off the coasts of New South Wales, Queensland (Australia) and KwaZulu-Natal, together with that of drumlines off Queensland has been very good. At Durban, from 1943 until the installation of nets in 1952, there were seven fatal attacks. Since the installation of nets there have been no fatalities at Durban and no incidents resulting in serious injury. At KwaZulu-Natal's other protected beaches, from 1940 until most of those beaches were first netted in the 1960s, there were 16 fatal attacks and 11 resulting in serious injury. In the three decades since nets were installed there have been no fatal attacks at those beaches and only four resulting in serious injury. Two of these occurred at Amanzimtoti, in 1974 and 1975, the third at Ballito in 1980 and the most recent at Umtentweni in 1999. It has been argued that the Amanzimtoti incidents represent only a partial failure of shark nets in that parts of the installation were out of order at the time and bathing and surfing had been banned. Such has been their success that a generation of KwaZulu-Natal residents has grown up in an environment virtually free from the risk of shark attack.
The KwaZulu-Natal coastline is often subject to large swells and strong currents, which may result either in the nets becoming entangled or the nets or drumlines being dragged out of position. The boat crews make every effort to rectify the problem when they service the equipment in the early morning but heavy seas and strong winds may make this impossible. Tangled or displaced equipment may no longer be able to fish effectively for sharks and, in the interests of public safety, all bathing and surfing is temporarily banned at that beach. As soon as the equipment is restored to normal working order, the ban is lifted.
Bathing may be banned even though the equipment is in order. This may take place if a large shark is sighted in the immediate vicinity of the bathing area or following the stranding of a whale or whale shark in the area, an event that is likely to attract sharks inshore.
Traditionally bathing has always been banned when the nets have been removed for the annual Sardine Run. This still occurs at a small number of localities, where discretionary bathing (see below) has not been accepted by the local authorities.
Discretionary bathing was introduced in the mid 1990s to allow people to swim and surf during the annual Sardine Run. At this time of year almost all the nets at beaches south of Durban are out of the water to avoid heavy mortalities of sharks and dolphins that follow the sardines. Although there are more sharks in the coastal waters of southern KwaZulu-Natal in winter than at any other time of the year, records from the period prior to the introduction of shark nets reveal a very low incidence of shark attack. In the past, pressure from the tourist industry often resulted in hasty reinstallation of shark nets during the Sardine Run. This frequently proved disastrous, killing large numbers of sharks and dolphins.
The advent of discretionary bathing has enabled the KZNSB to keep nets out of the water for as long as two months, thereby minimising the chances of large-scale mortalities. Unfortunately not all local authorities have accepted discretionary bathing and prefer to continue to ban bathing.