LISTENING out for whale song is one way that ships can avoid colliding with whales. But what do you do if the whales aren鈥檛 singing? One answer, developed by researchers in the Canary Islands, is to focus on the way the giant creatures mask the clamour of ocean noise.
No one knows how many whales are killed by ships each year, but collisions are thought to account for up to a third of unnatural deaths. For the northern right whale, this means one or two individuals every year, and with only 300 animals left, that鈥檚 an unacceptable loss.
And it鈥檚 not just conservationists who want a solution. Hitting a whale can do expensive damage to ships, or worse. A passenger on a fast ferry died in 1992 after being thrown out of his seat when the ship hit a whale off the Canary Islands.
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There are three global hot spots for whale collisions: northern right whales are at risk in the Atlantic off the east coast of the US and Canada, fin whales in the Mediterranean, and sperm whales off the Canary Islands.
Last year, the Massachusetts-based International Fund for Animal Welfare attached hydrophones to buoys and successfully listened out for right whale song in the North Atlantic. But since right whales remain silent for hours at a time, and sperm whales are silent for around half the time, a better tracking technology is needed.
The new Whale Anti-Collision System (WACS), developed by Michel Andr茅 at the University of Las Palmas in the Canaries, is designed to help ships in these hot spots steer clear of the whales. It uses a sonar technique called ambient noise imaging to locate the animals even when they are silent.
To do this, Andr茅 has been testing a long lines of buoys, each bristling with 32 sensitive underwater microphones, or hydrophones, that pick up sea sounds such as breaking waves, rain and shipping noise. Any approaching whale blocks this background noise and creates a detectable 鈥渟ound shadow鈥�.
By comparing the reflections received from the hydrophones on different buoys, Andr茅鈥檚 system can gather enough information to work out the whale鈥檚 position and how fast it is moving. Software displays the results on a 3D colour map. Underwater objects stand out like hot spots on a thermal image.
In trials planned for next year, Andr茅 will place two lines of 12 spherical buoys along the 120-kilometre ferry route between the islands of Tenerife and Gran Canaria. The signals will be sent to a land station where they will be analysed to create a 3D picture of the sea in real time.
If the trials are successful, the WACS software could be installed aboard ferries so that ships鈥� masters can steer clear of whales. Failing that, the whales鈥� movements could be tracked from shore-based installation and radioed to ships in the area.