Off the coast of western Australia, an attempt to seek vengeance against a great white shark this week lasted only two days.

Sharks have killed four people off Australia in the past 14 months, including three since early September. So when 32-year-old American George Thomas Wainwright was killed Saturday while diving, West Australian authorities issued an order to capture and kill the great white shark involved in the incident. They set six baited lines in waters off Rottnest Island, where Wainwright died, and shifted locations once in hot pursuit. But by Monday, they decided the shark had migrated far offshore, and they abandoned the effort.

The decision by Australian officials to exercise this authority for the first time — despite the target being an otherwise protected species — highlights the contradictory relationship humans now have with sharks. Some people would like to protect them in theory, but it’s harder to do it in practice.

The number of shark-related deaths this year — 13 worldwide — is nearly triple the annual average, prompting some coastal communities to take drastic action. But shark conservation measures are gathering momentum in the United States and abroad, as policymakers and scientists warn that the sea’s most feared predator is in danger of disappearing.

“It’s the ‘Jaws’ effect. There’s something primal about this fear of shark attacks that you don’t have with other animals,” said Maryland Del. Eric G. Luedtke (D-Montgomery), who is drafting a measure that would ban the sale, trade and possession of shark fins in Maryland. Luedtke thinks his bill stands a strong chance of passage next year, and he has watched the Australian hunt with dismay.

“It’s sad to see that, because it’s not going to make you any safer,” he said.

George Burgess, curator of the International Shark Attack File at the Florida Museum of Natural History, said no single factor explains what he called the “big jump” in the number of deaths this year. (The total number of incidents, including non-fatal encounters, 64, is in keeping with previous years.) Warmer waters in places such as the Sea of Japan, also known as the East Sea, could be connected to the unusual shark strikes off Russia, Burgess said, while human activities such as fish farming may have lured sharks to Reunion Island, east of Madagascar, where two deaths occurred.

This weekend’s shark hunt was the fifth this year, according to University of Sydney doctoral researcher Christopher Neff, marking what may be an all-time high. The other ones took place in the Seychelles, Reunion Island, Mexico and Russia. In almost every instance, communities sought to kill sharks after multiple attacks. The searches have had different stated aims: Reunion Island authorities said they were gathering scientific data by killing sharks, while Seychelles officials said they were paying fishermen for dead sharks in hopes of recovering the wedding ring of the British honeymooner who died off their shores. But in each case, officials emphasized they were seeking to protect the public.

In a statement, West Australian Fisheries Minister Norman Moore told The Washington Post that the multiple attacks were “an unprecedented circumstance which required an unprecedented response,” noting that his task was complicated because many people approach the waters of Rottnest Island from boats and might not see beach signs or patrols. He added, “There is no order to cull sharks — there is an exemption under the [law] that has always been there to take an endangered species if or when it poses an imminent threat to human life.”

Several experts, including Burgess, questioned whether targeting an individual shark would enhance human safety. More than 100 marine biologists wrote to Moore, as well as other state and local authorities, urging them to “realize that a shark cull would be disastrous not only to our marine environment but also Australia’s reputation as a world leader in marine conservation.”

A 1994 scientific study of shark-control efforts that Hawaii undertook between 1959 and 1976 found the measures killed “4,668 sharks at an average cost of $182 per shark.” But the authors concluded that they did little to affect tiger sharks, which were most likely to attack humans.

“Shark hunts are an example of a political effort to reduce the public perception of risk rather than real risk reduction,” Neff wrote in an e-mail. He added that governments would be better off investing in warning flags, message boards and announcements that “allow beach goers to see the ocean in a more complete way.”

Chuck Anderson, who lost his right arm to a bull shark in 2000 off Gulf Shores, Ala., urged his friends not to hunt down the shark he encountered. “What right do we have — even having my right arm ripped off — to start advocating to kill sharks, just to make us feel safer?” he asked.

Environmentalists have won a series of new protections for sharks this year, arguing that the predators have been decimated by indiscriminate industrial fishing and fishing for their fins, which are used in shark’s fin soup, an Asian delicacy. Between 26 million and 73 million sharks a year are targeted for their fins, scientists say, and roughly a third of all shark species face some threat of extinction.

California Gov. Jerry Brown (D) signed a shark fin ban this month, joining Washington, Oregon and Hawaii. Groups such as the National Aquarium are pushing for Maryland to become the first state on the East Coast to enact such a ban. Toronto, Canada’s largest city, enacted a similar ban Tuesday.

Andy Dehart, the National Aquarium’s director of fishes, said the group is pushing for legislation because after tagging sharks in Delaware Bay and maintaining them in captivity for 30 years, he and others are convinced that “they’re not well-suited for the pressure of a fishery that the shark fin trade is doing to them.”

In Florida, the state’s Fish and Wildlife Conservation Commission is poised to vote Nov. 16 to ban the harvest of tiger sharks and scalloped, smooth and great hammerhead sharks in state waters. Academics, such as University of Miami Rosenstiel School professor Neil Hammerschlag, who studies sharks off the Keys, have pushed for the measure.

But to people like George Wainwright, who lives in Panama City, Fla., protecting sharks seems like an anathema in the wake of his son’s recent death. “I can only say I wish I was there,” he said in a phone interview. “There has to be somewhere where you see people as more important than this shark.”