Early on a May morning back in 2003, I was on the research vessel Oceanus some 200 kilometers south of Long Island, N.Y., searching for something I had been chasing for years. It wasn't a white whale, but it was just as alive—and a whole lot bigger.
My scientific colleagues and I had jokingly referred to the enigmatic thing we were seeking as a UFO—for "unidentified floating object." To find our elusive prey, we had engineered a newfangled sonar system that operates at relatively low frequencies and installed it on Oceanus, which is operated by the Woods Hole Oceanographic Institute. After days at sea, we finally got our big break—strong echoes emanating from about 20 km south of our ship, where the water was roughly 100 meters deep. On our sonar displays, it looked as though something the size of Manhattan was perched near the edge of the continental shelf.
In some places, the seafloor sports some pretty rough topography, but our charts showed it to be flatter than Kansas around where we were. And the mysterious echoes we were seeing with our new sonar hadn't been apparent the previous day, so they couldn't have come from any sort of uncharted seafloor ridge. What's more, as we stared at the display for the next hour or so, we could see the structure it revealed gradually changing shape, which seafloor geology just doesn't do.
This was definitely a UFO, one the size of a large city. Such things had been detected before with other long-range sonars, and most specialists at the time believed that these enigmatic echoes stemmed from irregularities on or beneath the seafloor. These acoustic ghosts came and went, it was thought, because changes in the temperature or salinity of the ocean caused varying refractions and either strengthened or weakened the echoes. We had never believed that particular ghost story and suspected that these strange acoustic reflections in fact came from large groupings of fish. Here at last was our chance to find out.
We immediately radioed the news of our UFO sighting to colleagues on another ship that was equipped with conventional echo sounders, similar to the kind countless boaters use to check the depth of the water and to locate schools of fish. It took that ship hours to reach its target, but when it finally did, shouts came back over the radio: "It's fish!" We were seeing a massive shoal—a community of oceanic fish—in its entirety for the first time. The echo-sounding equipment available on most ships has a limited range and is able to sense only tiny bits and pieces of such large shoals. So until that time, nobody knew what such a large shoal looked like.
We were all immediately struck by the implications. These fish had come together in a group that was more vast than anything that had been seen before. And they were doing it in a very unexpected place: a shipping lane leading to New York Harbor, one of the busiest ports in the world.
I felt honored to have helped make this discovery in 2003, but almost immediately those feelings became mixed with ones of deep concern about how the new technology could be misused. These thoughts crystallized during a later expedition when our long-range sonar equipment detected strong echoes in the vicinity of Georges Bank, off Massachusetts, which had been a prolific source of cod and halibut for centuries before overfishing caused those fisheries to collapse. As before, we radioed another vessel with conventional echo sounders to investigate, and it confirmed that the echoes were indeed coming from a giant collection of fish. But soon after, the captain called me to the bridge and pointed to the radar screen. On it were blips that marked the positions of dozens of fishing boats that had converged on the spot of the enormous fish congregation after listening in on our radio communications, which we had naively sent on an open maritime channel.
That episode made it very clear that this new fish-finding sonar could wreak havoc on ecosystems around the world. Used responsibly, though, it could help marine biologists and fisheries managers follow fish populations in ways that were previously unimaginable.
The sonar system my MIT colleagues and I put together to chase UFOs is just the latest link in a long chain of technical developments that date back to World War I, when submarines first came into widespread use. With the advent of undersea warfare came an urgent need to detect, localize, and image submerged objects, sometimes over vast oceanic regions.
Of course, light doesn't penetrate far in seawater. The same is true for all but the longest radio waves. So the only practical way to sense distant objects is to use sound, which can travel great distances underwater—a fact that has been known for hundreds if not thousands of years. That's why governments around the world have for decades poured huge sums into studying the physics of long-range sound propagation and scattering in the ocean.
As a result, naval sonar systems grew increasingly sophisticated during the 20th century. By the late 1960s and early 1970s, some side-looking sonar systems were able to form images across several kilometers of ocean, revealing the first hints of unidentified floating objects. Some people hypothesized that these echoes came from fish, but that surmise hadn't been confirmed. By the 1980s and early 1990s, long-range submarine-hunting sonars gained the ability to scan the ocean in a full 360 degrees in azimuth, imaging the entire horizontal plane around them. By this time the navies of the world had begun to be really troubled by the many ghostly reflections these systems were detecting—things that had no ready explanation.
At this point my group at MIT became involved in a large experimental program sponsored by the U.S. Office of Naval Research, which included deep-ocean surveys around the Mid-Atlantic Ridge, the undersea mountain system that runs through the center of the Atlantic Ocean. There, we found that previously uncharted ocean ridges caused many of the UFOs we were seeing on our sonar screens.
Our sponsors in the Navy were thrilled. And they were eager—too eager as it turns out—to apply the lessons learned to explain sonar UFOs found in much shallower water, above the continental shelves. The problem was that most of those shelves, the underwater extensions of many continents, are essentially featureless plains, and they are very well charted. So it made no sense to blame UFOs on unknown seafloor topography. Many people in the Navy concluded that hidden geologic features of the continental shelves must cause these ghostly sonar reflections to form.