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    Here’s how communities around the world are trying to prevent shark attacks

    In Cape Town, teams of two specially trained lookouts, one on a mountain and one on the beach, use polarized sunglasses and binoculars to scan the water and sound an alarm if they spot a shark in the ocean.

    Since 1962, the government of Queensland, in northeast Australia, has captured and killed thousands of sharks using an extensive network of mesh nets and buoys with baited hooks strung hundreds of feet off the shoreline.

    In Western Australia, the government has spent $23 million on a shark-deterrent program that involves permanent barriers off six popular beaches, daily helicopter patrols, shark surveillance towers, and rebates for divers and surfers who buy devices that emit a shark-repelling electronic pulse.

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    All of the methods can claim some limited success in preventing shark attacks. But as officials on Cape Cod grapple with how to prevent fatal attacks like the one that killed a 26-year-old engineering student off Wellfleet last Saturday, researchers caution that nothing can fully protect swimmers from the exceedingly rare possibility of a shark bite.

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    “For 80 years, scientists have been trying to figure out what are the best ways to deter sharks from people, and, in my opinion, there are no silver bullets,” said Chris Lowe, a professor of marine biology and director of the Shark Lab at California State University, Long Beach. “There are no definitively effective tools.”

    Chris Neff, a shark bite researcher at the University of Sydney who wrote his doctoral thesis on policy responses to shark attacks worldwide and briefed officials at the Cape Cod National Seashore in 2014, offered a similarly blunt assessment of the many techniques used to prevent attacks.

    “The short answer is there’s not a lot that works,” he said. “There are so many variables at play that it really creates a problem for public safety officials.”

    A view of a beach with shark nets in Sydney, Australia.
    EyesWideOpen/Getty Images
    A view of a beach with shark nets in Sydney, Australia.

    Traditionally, shark hunts, or culls, have been the first and perhaps most primal response to shark attacks worldwide. But scientists argue that while such hunts may quench the public’s desire for vengeance after a brutal attack, they do little to reduce the likelihood of another one. In Hawaii, for example, a government-funded program resulted in the killing of 4,668 sharks between 1959 and 1976, at an average cost of $182 per shark. But Lowe and other researchers who studied the program found it did “not appear to have had measurable effects” on the rate of shark attacks in Hawaiian waters.

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    Giant shark nets and drumlines, or buoys with baited hooks, have been among the most common and arguably successful strategies used to prevent attacks in Australia, New Zealand, South Africa, and Brazil. In parts of South Africa, for example, where nets and drumlines have been used since the 1950s, officials have reported a 90 percent drop in attacks.

    But nets and drumlines have been widely criticized by scientists and environmental groups because they kill not only sharks but other sea creatures, such as whales, turtles, seals, and fish. Critics also warn that nets and drumlines are costly to maintain. And some studies question whether the nets are as effective as government officials claim.

    In December, an Australian Senate committee recommended phasing out shark nets and moving toward a series of nonlethal techniques such as subsidies for ankle-worn electronic devices that repel sharks. The committee also recommended immediately replacing lethal drumlines with “smart drumlines” that use a satellite-linked device to alert officials when a shark is caught on a baited hook. A crew is then deployed to haul the shark into a boat and release it further offshore.

    Neff said smart drumlines, which are used in New South Wales, on the east coast of Australia, aren’t likely to spread to the United States because the satellite-linked systems and labor involved in hauling and releasing hooked sharks are “really expensive.” Another high-tech product, called Clever Buoy, which claims to use sonar to detect sharks and immediately alert beachgoers, is not yet proven, Neff said.

    “The data on this is all really new,” he said, “and I’m skeptical of most of it.”

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    Some studies have shown the ankle-worn electronic devices, often sold under the brand name Shark Shield, can keep great white sharks 4 feet away from a piece of bait by interfering with their electrosensory systems. But Lowe said there’s “not a lot of good scientific evidence” backing them up and he worries that the devices give surfers a false sense of security so they “actually do riskier things wearing a device than nothing at all.”

    On Cape Cod, where great white sharks have been feasting on an abundance of seals, officials and volunteers have been tagging and tracking sharks, flying a spotter plane, posting warning signs on beaches, and encouraging beachgoers to check the Sharktivity app, which maps the location of tagged sharks and shark sightings.

    Last year, a Florida company tested large balloons outfitted with high-definition cameras along Cape beaches. But officials balked at buying the system because it cost $300,000 for 12 weeks of shark monitoring, the Cape Cod Times reported.

    State Representative Sarah Peake, who represents eight Cape towns, said local, state, and federal officials are discussing the Clever Buoy system and improving cellphone coverage or installing call boxes on beaches where cell reception is notoriously spotty.

    Killing the seals that are attracting the sharks is not an option because they are part of a giant herd that migrates from Sable Island, off Nova Scotia, so thousands would simply replace those that were slaughtered, Peake said. The seals are also protected by the Marine Mammal Protection Act.

    Researchers said any antishark measures are really about trying to reduce the probability of attacks that are already highly unlikely. Last Saturday’s fatal attack on Arthur Medici, the engineering student who was boogie-boarding off Newcomb Hollow Beach, was the first in Massachusetts since 1936.

    Last year, there were 109 unprovoked shark attacks and four fatalities worldwide, said Ralph Collier, director of the Global Shark Attack File, which tracks such cases. Given the millions of people who went swimming last year, “going into the water has to be one of the safest avocations you can engage in,” Collier said.

    Researchers said the best advice may be for beachgoers to swim in groups, close to the shore, at crowded beaches, where attacks are less likely. But Lowe, a surfer who grew up on Martha’s Vineyard, acknowledged even he doesn’t always follow those rules.

    “I don’t think we can ever stop this,” he said. “The only way to completely prevent this is to not let people go in the ocean, and I don’t see that happening.”

    Michael Levenson can be reached at mlevenson@globe.com. Follow him on Twitter @mlevenson.