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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.

Join the conversation

25 Comments sorted by

  1. Simon Mould

    Environmental Science Student

    Stop the sharks... Deprive the sharks of their business model... Buy the sharks... Turn back the sharks? No but seriously anything is smarter than killing the sharks.

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  2. Suzy Gneist

    Multiple: self-employed, employed, student, mother, volunteer, Free-flyer

    Thanks for such a sensible and well founded proposal. I hope this is implemented.

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    1. Michael Shand
      Michael Shand is a Friend of The Conversation.

      Software Tester

      In reply to Suzy Gneist

      you don't think it is slightly arrogant of us to now be claiming the sea shore as our domain?

      could it be the sharks are merely trying to tag us and release us back onto the land?

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    2. Allan Gardiner

      Dr

      In reply to Neville Mattick

      Unfortunately not Neville. It is never we humans who are fair, but only the sharks themselves, and they could give us a lesson or two on what it is to be fair, in that it's always been in their very nature to be nasty to everyone.

      If a shark lent you $100,000 at 80% interest would that shark then be known as a "loan human"? And if you didn't pay back all of the loan on time plus the usurious interest, and the shark had to tow you far out to sea by its taking the hard and fast line of demonstrably drumming-it-in to any others who might be entertaining thoughts of defaulting on their loans, and then it bit through the rope to leave you stranded way out there somewhere, would it be right and proper that the shark also be called a tow-cutter? Think about it.

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  3. David Semmens

    logged in via Twitter

    I wonder what survival is like in the released sharks? I'd reckon the tagging data could shed some light on that question.

    I also wonder why this works better than culling when killing and removing to another location seem to be functionally similar strategies?

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  4. Nina James

    logged in via LinkedIn

    I think this is the first smart thing I have read in response to the shark attacks. Having just seen 'Shark Harbour' doco- I think the idea of tagging and tracking is brilliant.

    To minimise attacks- perhaps introduce a live tracking App- so that swimmers and surfers can see whats in the water in those remote beaches- before jumping in.

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    1. Randall Owens

      Manager Reef Guardian Program

      In reply to Nina James

      The idea has merit and may be practical and would likely achieve both conservation and social outcomes in a structured and accountable way. As someone who has surfed and dived for much of my life on both sides of Australia I recognise that it is their domain I enter and I knowingly accept that risk. Having said that I was recently back in the West and I do recognise that it is an issue and was seriously unsettling a lot of watermen I have known for many years - this is seriously worth considering and costing

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  5. Liam Hanlon
    Liam Hanlon is a Friend of The Conversation.

    Student

    The problem with your idea is that it is based on evidence and well thought out policy...politicians could never implement such sensible measures. Reactionary populism is all they know.

    In terms of sharks coming closer to shore I wonder if it has anything to do with the depletion of fish stocks from overfishing leaving them needing to come closer to find food.

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  6. Comment removed by moderator.

  7. Vicky Wilson

    Retired

    Has our government provided any reasons as to why they have not considered or have rejected this alternative?

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  8. Michael Shand
    Michael Shand is a Friend of The Conversation.

    Software Tester

    The arrogance of humans

    this is the same arrogance that destroys the mangroves based purely on asthetics

    The ocean is not our domain, leave it alone, this is a dumb and wasteful idea

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  9. Russell Hamilton

    Librarian

    "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..."

    Those bits of information don't seem to fit well: attacks are rare and random, yet moving sharks in Brazil did have a result, but killing them in Hawaii didn't.
    Could the answer be that Hawaii is a breeding area they keep comg back to and hanging around, whereas they're just cruising past Brazil? In which case moving them might work for W.A. if they are just cruising by?

    (BTW what was the mortality rate for the people who had to take the hooks out of the sharks mouths before they were released?)

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  10. Julia Reisser

    Oceanographer, PhD candidate researching plastic pollution and sea turtles at University of Western Australia

    Very nice article. I hope it reaches the people in power. Proud of my UWA Oceans Institute colleagues! :)

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  11. Jim Cummins

    logged in via Facebook

    I suspect killing sharks in Hawaii made little difference because the islands have no continental shelf, so apart from local reef sharks most of the animals hitting the shore are probably coming straight off the deep ocean.

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  12. Allan Gardiner

    Dr

    Perhaps it's time we commenced training our clever friends the dolphins to affix a small inflatable balloon with a radio transmitter onto any large shark found swimming too close to shore, whether the shark is hooked on a drum line or just freely swimming about. The dolphins could be trained to target certain species of large shark and leave all else alone. We could place special underwater structures just offshore from all beaches where the dolphins could seek refuge in underwater airpockets if…

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  14. sully mac

    vagabond

    Hello Jessica, I was at your talk in Margaret River recently.
    Your solution about towing sharks out to sea has very obvious flaws.
    1, The most threatening and dangerous shark in the south west of W.A. (as it is responsible for all of the fatalities) is the Great White.
    2. At the talk in Margaret River, you described great whites "swimming straight past any drum lines and seldom being interested in them."
    3. Surely then, using bait on a drum line to lure in a shark that is not interested…

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    1. Jessica Meeuwig

      Professor & Director, Centre for Marine Futures at University of Western Australia

      In reply to sully mac

      Dear Sull

      Appreciate your post and thank you for raising queries on the non-lethal program that has been implemented in Brazil.

      I agree that in the southwest and Perth, it is white sharks that have been implicated in the recent spike of fatalities. However, when I indicated their lack of interest in bait, it was not with respect to drum lines but to our research baited video systems we’ve used to characterise WA’s shark and fish assemblages up and down our coast. These are designed to minimise…

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  16. Comment removed by moderator.

  17. Jessica Meeuwig

    Professor & Director, Centre for Marine Futures at University of Western Australia

    Howdy
    For those who are interested, there is a new paper out from Afonso and Hazin, the scientists that documented the value of the "tag and remove" program in reducing shark incidents in Brazil. It can be found here: http://www.sciencedirect.com/science/article/pii/S0022098114000410

    In this new paper, published in the peer reviewed Journal of Experimental Marine Biology and Ecology, they confirm that (1) tagged sharks don't tend to come back to areas used by beach goers, (2) post release survivorship can be high if you treat the animals right, and (3) that tiger sharks are experiencing high fishing mortality in their region. The relevance for our shark cull in WA relates to the fact that animals can be released alive if well treated - that is unlikely the case in WA where drum lines are set over night and that we are merely catching them as they move through. It is also a timely reminder of how vulnerable this species is to overfishing.

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