Great whites may be behind most attacks around Perth (Image: David Jenkins/Corbis)
Sharks have killed seven people off Western Australia since 2010. Can culling stop them – and what will be the cost to marine wildlife?
EARLIER this year, thousands of protesters gathered at Cottesloe Beach in Perth, Australia. Their message was rather surprising. . They were demanding an end to shark culling.
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The culling – or “localised shark mitigation strategy” as some politicians prefer to call it – was prompted by seven fatal shark attacks off Western Australia since 2010, which led to a fall in tourism and leisure activities. Baited drum lines were used to catch sharks off swimming beaches last summer, with the aim of killing any great white, tiger or bull sharks longer than 3 metres. Others were released if still alive. By the end of the first season, .
The state government claims the culling is essential to protect people and the state economy, and wants to continue over the next three summers. The protesters claim that culling doesn’t prevent attacks but does harm declining shark populations and marine ecosystems. So who is right? Does this kind of culling protect people? Is it a danger to sharks and other wildlife?
While it is easy to get the impression that shark culling is new, it has actually been going on for many decades in other Australian states and in South Africa. Early efforts to protect swimmers sometimes involved putting up barriers to keep sharks out of swimming areas without harming them. This exclusion method is still used today; fine-mesh nets keep sharks out around Hong Kong and around the world.
But at beaches where the surf is rough, frequent damage to barrier nets made maintenance very expensive and they were abandoned. Instead, local authorities turned to large-mesh gill nets placed several hundred metres offshore, beyond the surf. Some people assume these nets are there to keep sharks out, but actually the idea is to remove large sharks from an area by catching and killing them. The nets don’t fully enclose a beach, and over a third of sharks are caught leaving the area.
This kind of shark net was first in 1937, followed by KwaZulu-Natal province in South Africa in 1952 and in 1962. Queensland introduced drum lines at the same time. These fishing lines have one or more baited hooks, dangling from a floating drum anchored to the seabed.
Hundreds of sharks have been caught in these regions every year since the nets were implemented. So does this form of shark culling work? Before gill nets were introduced in the city of Durban in KwaZulu-Natal, there were seven fatal attacks between 1943 and 1951. Elsewhere in the province, 16 people were killed between 1940 and the 1960s, when the nets were used more widely. Since then, there have been no fatal attacks at protected beaches, although there have been a few non-fatal attacks. “The programme has been very effective,” says Geremy Cliff, chief researcher at the KwaZulu-Natal Sharks Board.
It seems to have made a difference in Queensland and New South Wales too, with fewer fatal attacks at beaches with nets and drum lines in place. And this fall has occurred despite the fact that activities like swimming and surfing have become far more popular in recent decades.
Critics of culling point to Hawaii where nearly 5000 sharks were killed between 1959 and 1976. Another 100 sharks were killed when the state briefly resumed targeted shark fishing in 1991 and 1992. Initially hailed as a success, . “Despite these efforts, people were still bitten,” says shark tracker Carl Meyer of the Hawaii Institute of Marine Biology.
Why didn’t culling work in Hawaii? One suggestion is that the culls were too sporadic. Another is that it’s due to the species of shark. In KwaZulu-Natal, most attacks are thought to have been by bull sharks, which are territorial. Once local bull sharks are killed, others are far less likely to take their place. In Hawaii, however, and .
Bull sharks may also have been to blame for many attacks in Queensland and New South Wales, but in Western Australia most incidents have been attributed to great whites, which can . Does this mean culling won’t work there? “It will be less effective,” says Cliff. But he thinks it will still lead to a drop in attacks.
Whale of a problem?
Others doubt it will make any difference. Peter Sprivulis, an emergency medicine doctor in Perth, migrating along the coast – the sharks feed on dead or . Shark attacks seem to be increasing in line with the growing whale population, Sprivulis points out.
Then there’s the environmental cost. Gill nets don’t just catch sharks, but also many other animals, including dolphins, tuna, turtles, rays and even the occasional whale. Some are released alive but many die. Drum lines catch fewer non-target animals but still take a toll.
Most studies have concluded that ongoing culling has only a minor impact. There have been big declines in some of the species caught in shark nets, such as dugongs off Queensland, but , such as seagrass loss due to pollution.
“Shark nets aren’t there to keep the animals out, but to catch and kill them”
It is impossible to assess the impact of culling alone, says Cliff, because it is happening alongside everything from pollution to global warming to illegal fishing. But there is a difference between continuing to cull in a given region and introducing the practice to another area: it is likely that culling has a big initial impact, and that populations then stabilise at a lower level.
Then there’s the bigger picture. Although Australia culls nearly 1000 sharks annually, this pales in comparison to . Worldwide, it is estimated that . “Dedicated shark culling programmes take far fewer sharks than industrial shark fin fisheries,” says Meyer.
For the protesters, though, the point is that the main target of the Western Australian cull is the threatened great white. It now has some protection in a number of countries, including Australia, so the cull required a special exemption. So far, however, no great whites have been caught in this region.
There are, then, no easy answers. It is far from clear what the environmental impact of the cull will be. It is also not clear if it will save lives. In other parts of the world, occasional spates of shark attacks have ended without any control measures, so it is certainly .
What is clear is that the popularity of shark fin soup is a far greater threat to sharks than culling – and drowning is a far greater threat to swimmers than sharks. On average, 120 people drown around Australia each year, compared with just – and yet somehow that doesn’t make us feel any safer going into shark-infested waters.
See what shark defences look like: “Five ways to keep sharks away from the beach“
This article appeared in print under the headline “Biting back”
