Sometime last weekend a three-meter female tiger shark snared itself on a hooked line that was attached to a floating drum just off the southwestern coast of Western Australia. A commercial fisherman later motored by and, with the blessing of the government, shot it in the head. Four times.

The controversial cull began this weekend as a response to the deaths of seven people over the past three years at the hands – er, teeth – of sharks in Western Australia. At a press conference the state’s premier, Colin Barnett, said, “I get no pleasure from seeing sharks killed, but I have an overriding responsibility to protect the people of Western Australia, and that’s what I’m doing.” Protecting swimmers and other beachgoers is indeed important, but are culls even effective in the first place? And are there other methods that are better able to both protect swimmers and the sharks that many would rather avoid?

While the scientific data on the effectiveness of shark culls is scant, what data is available suggests that they aren’t terribly effective. In a 1994 paper in the journal Pacific Science, University of Hawaii researchers Bradley M. Wetherbee, Christopher G. Lowe, and Gerald L. Crow took stock of nearly two decades of shark control programs in Hawaii.

The programs were implemented with two main objectives. The obvious aim was to reduce the number of sharks in the water. In addition, data was collected from the sharks that were captured in order to add to the body of knowledge on shark biology. If the sharks were going to be killed, at least scientists could benefit from the data. At least, that was the idea.

But Wetherbee and colleagues reported that only one scientific paper derived from the shark cull data was ever published. As a result, the reports made by those who carried out the culls went unchallenged by the formal peer review process. And while the reports declared the culls successful insofar as fewer sharks were caught as time went on, a correlation does not prove causation. The researchers point out that while “the removal of nearly 4700 sharks from Hawaiian waters over an 18-yr period undoubtedly resulted in a substantial decrease in the population, and declines in shark abundance are evident in reduced catch rates in long-running programs,” other factors that could have contributed to that decline were never considered, such as predictable seasonal shifts in local shark populations, or weather patterns, which not only drive changes in shark behavior but also have a tendency to foul fishing efforts.

More damning evidence comes from the finding that there was no statistical difference between the average number of attacks per year for the eighteen years prior to the first control program and the eighteen years in which control programs were intermittently implemented. “Consequently,” Wetherbee writes with an excessive amount of understatement, “conclusions made about the effectiveness of the programs in reducing shark populations might well have been stated with less confidence.”

If culls don’t seem to work, are there any other methods for making swimmers safer? Gill nets have been shown to be effective at reducing shark encounters, but they have the downside of indiscriminately catching dolphins, dugongs, turtles, birds, rays, tuna, other non-dangerous sharks, and even whales as well. And the removal of larger sharks from the sea by drowning them in gill nets has led to the proliferation of smaller sharks in some areas, which in turn compete with fishermen for the same fish stocks. Indeed, removing apex predators can have widespread effects on the entire ecosystem, something that was made obvious with the removal and subsequent reintroduction of wolves from Yellowstone National Park.

A 2013 paper in the journal Animal Conservation describes a more welfare-oriented, ecologically conscious approach to shark attack mitigation in Recife, Brazil. The problem was that 55 shark attacks were recorded along a twenty-kilometer stretch of coastline between 1992 and 2011, 19 of which resulted in fatalities. As a result, the state government created a Committee for the Monitoring of Shark Attack Incidents, which formulated a new strategy to manage the risk of shark attacks. The guiding principle was removing sharks from high-risk areas rather than from their populations. It was actually quite simple: sharks were captured, transported, and released farther from shore. If effective, the reasoning went, such a strategy would reduce the risk of shark-human encounters while also maintaining the structure of coastal ecosystems.

Not only did the catch-and-release method avoid creating a massive ecological upset, but it was also overwhelmingly effective. Between 2004 and 2011, the shark relocation program was in operation for 73 months, and was inactive for 23 months due to funding shortfalls. Thus, researchers were able to compare the frequency of shark attacks while the program was active to months it was on hold. While the program was operational, Recife saw an impressive 97% reduction in the monthly shark attack rate.

While the shark cull program began in Western Australia last week, groups of Japanese fisherman continued their annual dolphin slaughter. It is perhaps not surprising that the kind of outrage directed towards the Japanese town of Taiji has not been aimed towards Western Australia. The cultural narrative that surrounds dolphins is one of friendliness. Dolphins are thought of as smart, playful tool-users, their faces plastered in a permanent smile. Sharks, on the other hand, are traditionally seen as little more than sets of flesh-shredding steak knives with fins. Of course neither tale is complete. Dolphins can be jerks and sharks can actually be quite clever. As shark scientist David Shiffman wrote in a recent blog post, perhaps the best strategy to avoid the needless slaughter of sharks is simply better education. Maybe swimmers can simply be taught the most effective behaviors for reducing the risk of an unfortunate encounter. Combined with a catch-and-release program, humans could then safely enjoy our brief visits to the sea. – Jason G. Goldman | 29 January 2014

Sources:

Wetherbee B.M., Lowe C.G. & Crow G.L. (1994). A Review of Shark Control in Hawaii with Recommendations for Future Research, Pacific Science, 48 (2) 95-115.

Hazin F.H.V. & Afonso A.S. (2013). A strategy for shark attack mitigation off Recife, Brazil, Animal Conservation, n/a-n/a. DOI: 10.1111/acv.12096

Photo: Tiger shark via Wikimedia Commons/Tony Hisgett.