Shark Spotters flags

Article: Outside on tiger sharks in Hawaii

Hawaii is one of the places on earth where an enlightened government is working for mutual safety of the local shark population, and the surfers, swimmers and other water users who occasionally happen upon sharks in their natural habitat. Like our local Shark Spotters program, non-lethal methods are used to manage the chance of human-shark interactions.

Starting in the 1950s, the Hawaiian government killed thousands of sharks as part of a culling program, believing that sharks were territorial and that eliminating a shark seen near a beach would be removing it from its residence, making the beach safer.

Carl Meyer of the University of Hawaii was part of research begun in the 1990s that tracked tiger sharks with hydrophones. Researchers saw immediately that the sharks were not resident in one location but, much as great white sharks do, they range widely. As a response to the very first tracking study, the state of Hawaii stopped hunting sharks after they had bitten humans, as the evidence indicated that the responsible shark would be long gone before a “cull” could be instituted. Meyer says in an interview with Outside Online:

So clearly, there were two broad lines of evidence that this shark control stuff was worthless. One was critical tracking data showing that these sharks were much more mobile than people believed. The second was that people were still getting bitten at sites from which many tiger sharks had already been removed by control fishing. So there’s just no evidence that shark culling makes the water safer. It’s just not demonstrably effective.

Both Western Australia and Reunion Island (a French territory in the Indian Ocean) have decided recently to hunt sharks after fatal interactions with humans. Meyer explains why localised spikes in shark bites occur, dismissing many of the (understandable) conclusions that people rush to without recognising the inherent variability of natural systems (emphasis mine):

What you tend to have is a typically low number of shark attacks, and over time you might see some spikes in the number of bites. It doesn’t mean there’s any fundamental change in marine ecosystems. It doesn’t mean, for example, that a bunch of sharks have moved into your area. It might be nothing more than natural variability, which occurs in marine or terrestrial systems. Nature is an inherently noisy system. Part of the noise is variation in stuff, including the number of people that get bitten by sharks.

Meyer also discusses the behaviour of sharks around fish farms: they seem to be attracted to the net structures out at sea, although they do not seem to actually eat the fish in the farms. He suggests that the large three dimensional structures of the farms, alone in a vast and featureless oceanscape, are interesting in the same way that a shipwreck or other artificial reef is to a fish. I found this fascinating, but it is not a completely outlandish idea that a creature as intelligent as a shark would perhaps derive visual stimulation from something like a fish farm. He also theorises that they could be good meeting places to hook up with other sharks!

Finally, he touches on the cage diving operations in Hawaii.

Another issue which has generated a lot of heat here in Hawaii and elsewhere is shark cage diving ecotourism. These activities have proven hugely controversial. We’ve done a fair bit of work on the one here on Oahu, including a meta analysis of logbook data and tracking long-term movements of sharks captured at the cage diving sites—the takeaway message is that there’s absolutely no scientific evidence whatsoever that the existing operations off Oahu are a threat to public safety, which has been people’s major concern.

The findings he reports are similar to those reported for False Bay’s white sharks.

Read the full interview here. It contains incredibly important information and principles. It explains how scientists think about animal behaviour, gather evidence, and draw conclusions. Even if you don’t follow any other link I give you this year, please follow this one. Do it!

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Lapsed mathematician, creator of order, formulator of hypotheses. Lover of the ocean, being outdoors, the bush, reading, photography, travelling (especially in Africa) and road trips.