Low-frequency sonar is a boon to both marine biologists and the commercial fishing industry
Since submarines began roaming the depths in World War I, sailors and oceanographers, who use sonar technology to map seafloor topography and identify ocean life, have regularly run into “acoustic ghosts”—inexplicable bodies of movable mass that sometimes rivaled the size of a city—writes ocean engineering professor Nicholas Makris in IEEE Spectrum (Aug. 2011). Affectionately called UFOs (unidentified floating objects), these sonar readings were blamed on factors as various as deep-ocean mountains and changes in water temperature. Every time a theory emerged to explain the phenomenon, however, it was quickly shot down.
In 2003 Makris and fellow scientists aboard a research vessel just south of Long Island, New York, discovered that the UFOs were composed of hundreds of millions of fish—massive gatherings on a scale never before documented. Using low-frequency sonar technology that penetrated hundreds of miles, they identified a school roughly the size of Manhattan. A follow-up expedition revealed yet another gigantic shoal off the coast of Massachusetts. “It wasn’t a white whale,” writes Makris, “but it was just as alive—and a whole lot bigger.” (To put it in perspective, a sperm whale like Moby-Dick might reach 22 yards.)
The jubilation surrounding their discovery lasted as long as it took to radio the news to another research vessel on an open maritime channel. Overhearing the dispatch, dozens of commercial fishing boats sped to the site. The implications were enormous. “That episode made it very clear that this new fish-finding sonar could wreak havoc on ecosystems around the world,” Makris writes.
Makris and his team are set to launch, early this year, a streamlined sonar system that is smaller and lighter. But they’re keeping close tabs on the use of the technology and are working to ensure that its primary purpose remains scientific. “The oceans cover nearly three-quarters of Earth’s surface, yet to this day they remain dark and largely unexplored frontiers. By casting some light on the ocean with side-area sonar, we hope we can help to preserve marine life,” Makris concludes. “Used responsibly—perhaps by delaying the release of the data for a month or two—the information gleaned would provide marine biologists with a valuable scientific resource without compromising the sea creatures it reveals.”