Tracking large sharks sounds good on paper, but what’s required for the sake of beachgoers, to stalk these marine predators and report their whereabouts?
Queensland’s Surf Lifesavers on the beaches of North Stradbroke Island are testing small, unmanned aircraft (drones) to collect such information. In New South Wales, the Department of Primary Industries is also running experiments. But in 2012, the same department published a study testing the usefulness of aerial beach patrols done by pilots in helicopters or small planes. Such patrols spot very few sharks, about one per hundred square kilometres. This is most likely a serious underestimate. Can mechanical observers, peering through the same murky water and to varying depths, do any better? Before speeding along with some technological fix, let’s take an ecological reconnaissance of white, bull and tiger sharks.
Australian great white sharks (Carcharodon carcharias) are not common and in decline. Marine biologist Berry Bruce tagged 500 individuals in Southern Australia around Neptune Islands. A decade of monitoring reveals that these great whites often make great annual migrations. In the winter they travel along the coast up to south-east Queensland and then return south during September and October. This tracks the migration route used by humpbacks who hug the coastal shallows to protect vulnerable young against shark attacks.
As great whites attack from below, they start at depth and accelerate vertically to ram and stun their prey. If they are only curious and exploring an object in the sea, they swim up to it sideways to ‘mouth’ and ‘taste’ it. That’s why specialists say people in shallows are not the usual prey of great whites. Unfortunately the animals are too strong for such investigations to be harmless. In one behaviour study, great whites will test and then eat a fat, high food value pig but test and refuse leaner sheep, who, like people, carry much less fat.
Bull sharks (Carcharhinus leucas) is classified as ‘near threatened’. But it is more often seen because the adults tend to patrol shallow coastal waters often near the mouths of estuaries and rivers. The young use the upstream waters. They are ambush hunters of murky waters, whose strategy is ‘bump and bite’. They scavenge through cloudy waters chasing contrasting colours, which could be something edible. They are also territorial.
Tiger sharks (Galeocerdo cuvier) are another ‘near threatened’ species, who live in the same zone as bull sharks but travel further and range deeper. They are solitary hunters who also ‘bump and bite’, coming inshore at night.
These three sharks are not attacking more people now than before. There are simply many more people in the water. Sensible precautions are to avoid murky water, especially a day or two after rain. Avoid the water at dawn, dusk or dark. Swim or surf as part of a group. Avoid the water where seabirds or dolphins are feeding. Sharks often join them. If you see a dangerous shark, keep watching and quietly get to shore. Some specialists, including Australian filmmaker Val Taylor, report that punching back at sharks that bump you is so surprising to these top predators that they back off. They don’t expect a challenge.
Much of this ecological information comes from research using tags: either acoustic, satellite or ‘pop up’ devices. These devices are expensive, complicated and invasive for the sharks themselves. Some tagging interferes with the shark’s survival skills. Interestingly, some types of tagging projects improve when they include the sightings of divers, fishers and other observers with first-hand experience of a marine place.
Knowing a place, much as knowing a person, offers unexpected relationships. In Hawaiian lagoons and beaches, traditional shark keepers knew the territories and movements of their local and migratory sharks. They fed and petted them. They swam with or rode on them. They felt recognition and respect was mutual. They also expected help with fishing from these, their local gods.
Technology offers great data, within sharp limits. But what more could we know and be if we deeply engaged with our marine places? What more than fearsome is part of the personality of a shark?
SharkSmart app: https://itunes.apple.com/au/app/sharksmart/id915621811?mt=8