Are There White Sharks Swimming Among Us?

The company Strava was in the news recently for its ability to display highly accurate maps using position data from personal fitness devices (e.g., Fitbit, Apple Watch, etc.). Not only are GPS fitness devices tracking a person’s mileage on land, many also track water activities, such as swimming, to within a few meters.

The other day, we had a great question from an avid swimmer who trains in Monterey Bay. Could he use the kind of white shark tracking data we have on our Ocean Tracks website, and determine whether he was working out alongside white sharks?

The short answer is no, not really – at least not with the technology that is currently being used. But here's a more detailed answer:

The Block Lab, which is the source of our Ocean Tracks tracking data, uses a couple of different tags with white sharks. Pop-up Satellite Archival Tags (PATs), which are used to create the kind of tracks on the Ocean Tracks website, provide daily position data based on a combination of sunrise/sunset curves and sea surface temperature. This means that they provide only one position per day, and each position typically has an error on the order of 1° in longitude and 2° in latitude – which is fine for tracking an animal across an ocean basin, but is useless for doing meter-scale mapping of behavior. 

A second type of tag, called an acoustic tag, produces a unique, coded “ping” which can be picked up by underwater receivers when its wearer comes within about 500 meters. By setting up networks of such receivers, scientists have been able to follow tagged fish with a very high level of accuracy, by triangulating the position of each “ping” from the length of time it took for that ping to hit each receiver. However, for white sharks, the Block Lab researchers typically only set up one or two receivers in key locations – which is useful for telling them when a shark has arrived at a certain spot (say near an elephant seal colony where they’ll spend the fall and winter months) – but not very useful for tracking smaller-scale movements.

Real-time satellite tags can provide much higher resolution position data than PATs or acoustic tags, as long as the tag is held out of the water for at least 20-30 seconds at a time. However, they typically offer less data about temperature and diving behavior, and are also much more difficult to attach than either PATs or acoustics. (Satellite tags typically require that the animal be lifted on a sling and handled for at least a few minutes, whereas acoustic tags can be deployed as the shark swims by under the boat!)

As with all microprocessor-based products, animal tracking tags are becoming smaller, lighter, and more powerful as the years go by. It is not difficult to imagine that one day we’ll have a tag that will be easy to deploy, and will provide reams of real-time (or near-real time) data about an animal’s behavior and surroundings on an ongoing basis. Not only will these tags give us deeper insights into the way that animals use the oceans, but they will also provide us with richer sources of data for studying and forecasting subsurface “ocean weather,” which is of great interest not only to the scientific community, but also to commercial shipping, fishing, and defense industries. Until then, though, we’ll just have to use what we know about when and where sharks tend to be before we jump in.

 

 

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