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Towing sharks out to sea will let us protect people … and sharks

The discussion about Western Australia’s proposed shark cull is highly polarised, and has unfortunately been framed in some popular media as a case of “them or us”. But what if there was a way to protect…

Tag and release: a science-backed alternative to shark kills. John Rumney

The discussion about Western Australia’s proposed shark cull is highly polarised, and has unfortunately been framed in some popular media as a case of “them or us”. But what if there was a way to protect people and sharks?

Well, there is: you just tow big sharks out to sea and let them go. And unlike the WA government’s cull policy, this idea is actually backed up by scientific evidence.

The idea has already been tried in Brazil, where it reduced shark incidents by 97% with minimal environmental impact. By partnering with scientists, the government has reduced the risk to ocean users without resorting to killing threatened species.

A science-based approach

The focus of Brazil’s program is on capturing, tagging, and releasing healthy sharks offshore, away from popular beaches, rather than killing them. It uses a combination of bottom long lines and drum lines to catch tiger, bull, and hammerhead sharks within 2 km of the shore. Once captured, the sharks are brought onboard and carefully placed in a tank filled with running seawater, before being measured, sexed, tagged and finally released about 8 km from shore. To reduce environmental impact, all other shark and bycatch species caught are immediately released at the site of capture.

This approach could be integrated into the existing tagging program run by the WA Department of Fisheries to create a mitigation program that gathers valuable scientific information on shark movements while also increasing public safety at beaches.

Given the WA government’s decision to have the Department of Fisheries kill sharks off Perth, rather than giving the job to private contractors as originally planned, there is now a clear opportunity to replace culling with tagging, in which the department already has significant expertise.

The problem with the WA plan as it currently stands is that it is unlikely to resolve the issue of shark bites. Federal environment minister Greg Hunt, in approving the plan, described the use of drum lines to kill sharks and other species as “in the national interest”. But it’s only in the national interest if it works. In reality, it is more likely to create a false sense of security than offer real protection.

Does culling work?

Contrast Brazil’s experience with that of Hawaii, where more than 4500 sharks were killed between 1959 and 1976. There was, however, no significant decrease in the rate of shark bites.

What’s more, shark bites are rare and random events, which makes it difficult to measure the success or otherwise of previous drum lines or netting programs such as that in Queensland. As recently as 2012, a report commissioned by the WA government rejected the use of drum lines as an effective option to reduce shark bite risk.

Culling may actually increase safety issues where drum lines are deployed near the coastline. The proposed round-the-clock deployment just 1 km off the WA coast means that catches are likely to be unattended for long periods of time, resulting in the death of captured animals. These carcasses can potentially attract larger sharks. Indeed, a 2010 cluster of shark bites (five incidents in four days) at Sharm el-Sheikh in Egypt was found to be related to the large number of sheep carcasses being disposed of at sea.

The proposed culling program also has the potential to undermine the science needed to mitigate risk to ocean users. The existing tagging program implemented by the WA Department of Fisheries will be ineffective if the animals being tagged are killed. Consequently, we would lose key information on the movements and behaviour of these animals that directly informs education and awareness programs.

What’s more, resources previously allocated to tagging may be diverted to culling – a very real possibility given the department’s new responsibilities in terms of implementing the cull, leaving us hamstrung in our capacity to understand these animals.

Tag team

The science provided by tagging programs is important. Such studies have shown that large species such as tiger sharks resume their migration patterns after being released offshore, and do not return to the areas where they were initially caught. Similarly, research on great white sharks shows that some individuals tagged off South Australia migrate along the WA coast, stopping in areas of abundant food for short periods (days to weeks), before resuming their migration to more remote areas. These data suggest that great white sharks using the coastal metropolitan waters of Perth do not live there.

Yet more tagging research in New South Wales identified an aggregation of white sharks off an unprotected beach where there has never been an incident.

A more comprehensive tagging and monitoring program will help us understand the movements of these transient animals, allowing us to work out when and where they are most likely to be found, and the environmental factors that drive these patterns.

Killing sharks is not only bad for sharks but bad for the ocean. Populations of sharks are declining globally. Large sharks are particularly vulnerable because they grow slowly, reproduce late and have few young, a set of traits that means the white shark’s effective population size is still low. Indeed, its historical overexploitation and low recovery potential has led to the legal protection of the white shark in Australia.

Increasing evidence suggests that sharks are also important in maintaining healthy reefs (see here, here and here for examples).

Renewed pressure on these populations through an uncontrolled culling program cannot be supported without evidence of two things: first, that these endangered species can cope with the extra deaths; and second, that such a program will actually increase human safety.

Scientific knowledge and technology can help us design a credible program that will increase the safety of people from sharks, while being less detrimental to the environment. We strongly encourage the WA Government to revise its policy from culling to tagging.