Archiving underwater sounds

Assembling a pop-up at the Cornell Lab of Ornithology.
David O. Brown/CLO

The "pop-up" marine recorder

Before scientists at the Bioacoustics Research Program invented auto-detection buoys, they had another tool for studying whale sounds: the marine autonomous recording unit, or “pop-up,” developed in the late 1990s. Whereas auto-detection buoys quickly analyze sounds looking for a single type of call, pop-ups listen for months at a time, recording everything they hear for a more thorough analysis later on.

Essentially, a pop-up is a hydrophone, an 80-gigabyte hard drive, and a microprocessor that oversees communication between the two. A set of batteries provides power, and a 17-inch-diameter glass sphere keeps the system waterproof to depths down to 3.7 miles (where the pressure is about 600 times that of the atmosphere).

Ears at the sea floor

While at work underwater, pop-ups float just a few feet above the sea floor, held in place by a cable attached to an anchor. When researchers come back, months later, to retrieve the device, they beam an acoustic signal into the water. Hearing it, the pop-up severs its attachment to the anchor and floats back up to the surface, bearing thousands of hours of recorded sound.

As of 2008, a total of 39 pop-ups monitor right whales around the liquefied natural gas terminal in Massachusetts Bay, in Stellwagen Bank National Marine Sanctuary, and in Cape Cod Bay, a critical right whale feeding area. The pop-ups are arranged in a grid so that many instruments can pick up the same whale call. 

Pinpointing calls

The duplicate recordings are each marked with a precise time-stamp, allowing researchers to calculate where whales were when they called. The information helps them learn about how right whales behave--something we still know little about. The precision afforded by the arrays and their continuous coverage also help in studies of the noise levels in Massachusetts Bay, including noise associated with construction and operation of the gas terminal.

Since their invention about 10 years ago, pop-ups have been adopted by researchers studying many other marine animals. They’ve also been used to study right whales beyond Massachusetts Bay, including in the Bay of Fundy, the Great South Channel off Cape Cod, in waters off New York, New Jersey, North and South Carolina, and at the critical right whale calving grounds off Georgia and Florida.

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