FIRST it was fish vying for title of the world鈥檚 smallest vertebrate, now there鈥檚 a new fish record in the offing. A novel sonar technique has captured what is reputedly the largest massing of animals ever recorded.
A shoal of more than 20 million fish was imaged using low-frequency sonar by mechanical engineer Nicholas Makris and his team at the Massachusetts Institute of Technology. Fish are usually tracked using high-frequency sonar beams, but these dissipate within about 100 metres, meaning you can only monitor a small area around you.
Makris and his colleagues realised that because low-frequency sound waves travel much greater distances, they could use them to rapidly scan areas of 10,000 square kilometres or more (Science, vol 311, p 660).
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They have monitored shoals covering up to 30 square kilometres off the coast of Long Island in New York.
