Sharks in the Water


Melanie Martella 

>> Today at Sensors Archive 

A recent article on the Australian POST Web site talked of a new project to install shark listening stations off the Cottesloe and North Cottesloe beaches in Perth, Western Australia, to provide a real-time warning of when sharks are near beaches, thus avoiding unfortunate human shark interactions.

The system, which has been used successfully in South Australia, was developed by the Australian Commonwealth Scientific and Research Organization (CSIRO), and uses listening stations to detect battery-powered tags attached to the sharks.  When the tagged shark gets within 500 m of one of the lsitening stations, it sets off an alarm.

One of the main benefits is that the sharks that have strayed into human-infested waters can be monitored immediately; previous systems relied on retrieving tags that had broken clear of the sharks and then downloading the contents to learn where the shark had been--handy if you're studying shark behavior and mapping territory but not so handy if you want to know if surfing in the ocean is more hazardous than you'd like.

The Humble Shark
Before I started researching for this blog entry, the sum total of my knowledge of sharks was that they were large, had many teeth, and would attack boats. Watching Jaws put the frighteners on me for years.  I knew that they could detect tiny concentrations of blood in the water and that groups of sharks could enter a feeding frenzy. I knew that they sank if they stopped swimming.

What I didn't know is that the only reason they float is their oily liver that gives them some limited buoyancy, that they can detect electric fields produced by living things (and that they do, in fact, sometimes attack boats but only because they've mistaken the boat's corrosion-related electrical field for lunch), and that the lateral line sense organ will detect movement and vibration.

Tracking Predators
As I've mentioned in previous blog entries, there are lots of projects afoot to tag oceanic denizens to figure out where they go: predators, food fish species, turtles, you name it.  Tagging predators such as sharks is a powerful tool both to understand them and to avoid shark attacks on humans. If you know where the sharks' general travel paths are,  you can keep people (their potential snack) away from those paths.  If you're interested in seeing the current list of shark attacks you can look here.

A Humorous Aside
For those of you who are fans of the movie Jaws, there's an entire Web site devoted to the movie.  And if you're short on time, you can watch Jaws as re-enacted, in 30 seconds, by cartoon bunnies.

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