Do shark nets and drum lines make beaches safer, and what else do they catch?

Nobody can say for certain that nets and drum lines make beaches safer, and they certainly catch more than sharks. Supporters and critics read the same record in different ways.

A shark net is a submerged wall of gillnet placed off a beach to intercept large animals, including sharks, with the aim of reducing attacks on swimmers. A drum line is an unmanned trap that lures large sharks onto baited hooks. Nets do not completely prevent attacks in the enclosed area. They work on the principle of fewer sharks, fewer attacks.

Supporters point to the record. From 1900 to 1937, 13 people died after shark attacks off New South Wales surf beaches. Over the next 72 years the number fell to eight, only one of them at a meshed beach. In KwaZulu-Natal, South Africa, nets were first deployed in 1952, and between 1990 and 2011 there were three attacks, none fatal, at protected beaches, against 20 fatal attacks at unprotected beaches elsewhere.

Critics point to the cost. They say nets are unethical and harm the marine ecosystem, and that no science shows nets make the ocean safer. Only around 10 percent of the catch is the intended target species, and the bycatch includes threatened species such as turtles, dugongs, dolphins and whales. Environmental groups also note that 65 percent of shark attacks in New South Wales occurred at netted beaches.