To see entire pelagic communities in the open sea, the Acoustical Ocean Ecology Group uses an instrument known as an echosounder. These instruments emit several sound frequencies from tens of kilohertz up to several megahertz from transducers, a device that serves as both an underwater speaker and a microphone. When these different frequencies reach organisms, they are either absorbed or reflected back to the transducer. Depending on how these sound waves are returned to us, we can determine the type of organisms present. The swim bladder of a fish, for example, reflects sound at a wide range of frequencies —therefore returning more of a signal to a transducer—than the chitinous body of krill which only reflects at relatively high frequencies.

Additionally, we are interested in how the presence of observational tools like ROVs impact the behaviors of pelagic organisms. On one field expedition, we identified an aggregation of animals approximately 60 meters ahead of the ROV—and out of the camera’s view. This large group of animals remained consistently 60 meters away until the lights of the ROV were turned off, which allowed us to approach. However, turning the lights back on caused the organisms to quickly swim away. The camera was only able to catch a glimpse of fins before the organisms, revealed as some sort of fish, were gone. With the ROV alone, the nearby school of fish would never have been discovered.