The view from the flying bridge of the Acoustic Explorer allowed good visibility and use of "Big Eyes" binoculars. (The observation crew was "off duty" at the time this photo was taken.)

In the fall of 1995, many of the Bioacoustics Research Program (BRP) staff spent several weeks aboard a research ship off the coast of California, observing and recording whales.

Dubbed "Whales '95," the expedition was funded by the U.S. Navy. Its principal goal was to compare two methods for censusing large whales from a moving ship: traditional visual counts, and acoustic counts, in which observers estimate the number of whales in an area based on the number of vocalizations they detect (much the way birders count birds by listening for their songs).

Biologists have long censused whales from aircraft or ships, counting how many animals they see at the surface. But trying to detect whales by sight alone is like birding in a dense forest with your ears plugged. The animals you seek may be hidden from view, and when they briefly show themselves (surfacing to breathe), you may be looking in the wrong direction. Or in moderately rough seas, you may not be able to discriminate the puffs of vapor exhaled from their blow holes from the crashing of two waves together. These problems can be overcome with careful listening; listening is also a way to detect animals too far away to be seen.

Until now, most biologists lacked the specialized equipment and experience required for underwater acoustic monitoring. Whales '95 brought together an unprecedented combination of visual survey experience and acoustic detection capabilities, as BRP staff members joined forces with visual observers from the National Marine Fisheries Service aboard the 130-foot research vessel Acoustic Explorer. To maximize the chances of seeing and identifying whales, four or more observers stood watch on the flying bridge (top photo) throughout the daylight hours.

Meanwhile, the ship towed a mile-long cable carrying 16 underwater microphones, or hydrophones, that recorded whale sounds; in the on-board acoustics laboratory (center photo), researchers used specialized computer systems developed at BRP to monitor the sounds as the hydrophones detected them.

During two 10-day cruises in an area about 200 miles west of San Diego, the BRP biologists saw blue, finback, minke, and humpback whales, as well as several species of dolphins and porpoises. On several occasions, whales came within 20 meters of the ship and the hydrophone array; perhaps they were curious about the bright yellow cable (bottom photo) being towed behind the ship or the strumming sounds the cable made as moved through the water.

The BRP crew brought thousands of recordings of individual whale calls back to their home at Cornell Lab of Ornithology, including some call types from finback and blue whales that had never been recorded before. As expected, the team never saw some of the animals they recorded, and some whales they saw were apparently silent.

Although it will take months of analysis to determine the best way to combine the acoustic and visual data, the project has demonstrated that biologists can detect many more whales when they listen as well as look.