Seeing sharks from space

There's always been an air of mystery around whale sharks. They may be the biggest fish in the sea, but they're also quite rare and have a habit of taking solo journeys around the globe's equatorial waters, making them hard to get a handle on. At least, that's what marine ecologist Brad Norman found back in 1994 when he first began studying the species at the isolated Ningaloo Marine Park, some 1200 km north of Perth in Western Australia.Ningaloo is one of the few places that whale sharks (Rhincodon typus) congregate with any regularity. Despite its remoteness, some 5,000 people make the trek up there each year to swim with the gentle giants and wonder at the constellations of dots and lines that mark their backs. The patterns of those dots are a kind of fingerprint – each shark's back carries its own distinct pattern.For Norman, it was clear that documenting them might offer a means of 'tagging' the fish to help cut through some of the species' mystery. So for the past decade he has been taking photographs of individual whale sharks and collecting them in a database for use in building a better picture of their life cycle. To help add to this data, he and others also founded a non-profit organization they called ECOCEAN, which operates a web-based whale shark photo library that anyone can contribute to.Over the years, the library has grown substantially, and now contains around 3,000 photos. "It's expanding every day," Norman says. "Now, we've got people sending photographs in from 25 countries."That's a potentially valuable resource for marine ecologists. Comparing photographs from across the globe could help track migration, age of maturity, growth rate and foraging ecology. The problem was that while doing that by hand might have been possible in the early days, the growth of the database soon meant it became impossibly labor-intensive. So, like very few marine ecologists before him, Norman turned to an astronomer for help.It all happened because software specialist and fellow Ecocean member Jason Holmberg – who had built the database for storing shark pictures – knew an astrophysicist by the name of Zaven Arzoumanian, from NASA's Goddard Space Flight Center in Maryland. Holmberg explained the problem, and Arzoumanian suggested they might want to try adapting an algorithm first developed to locate stars and galaxies in the night sky, as a means of identifying whale sharks by their distinctive patterns.The algorithm, used by the Hubble telescope, uses a machine vision technique known as 'blob extraction' to measure the locations and dimensions of pixel groups of a single color. "The spots on the whale shark are very like stars in the night sky," Norman explains. He and his colleagues set about modifying the star algorithm for use with shark skin – specifically, the area just behind the gill slit."It's taken years of refinement and tweaking, but now we've got a very successful program," he says. "If we were going to try to match photograph A with the other 3,000 by hand, it would take forever – this system makes it much faster."Considering whale sharks have been declared a threatened species, the computer-aided identification technique and photo library could have a profound impact on their management and conservation, Norman says. "These guys are pretty hard to study, so it's been positive to work out a way to monitor them," he explains. Knowing more about their population size, structure and evolution can help inform decisions about where to target conservation efforts.It's also nice because the Ecocean system helps the everyday public engage in conservation, he says. Every time a match is made with a photo in the database, the contributor is sent an automatic email telling them the shark he had previously observed, has been resighted again. It's great, Norman says, "you can be Joe Public, take a photo and make a contribution to science."

Seeing sharks from space

There's always been an air of mystery around whale sharks.

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