(This post was originally published September 24, 2021. Posts have been manually reordered for more logical storytelling. To go to the next post in the sequence, click “Previous Post” at bottom.)
Think of a command center — a single person monitoring many screens all around them. This is what we acousticians call home while at sea. On the Gyre Expedition, we listen to sounds in the ocean in real time, detected by a long cable containing underwater microphones (known as hydrophones) towed behind the research vessel Pacific Storm. We use a variety of software tools to visualize these sounds, because our human sense of vision is much better than our sense of hearing (unlike the beaked whales and other marine mammals we study).
Sound is measured on a frequency scale, and our hearing has evolved to be sensitive to frequencies important to us. As we age (starting as early as 20 years old), our hearing deteriorates over time, especially for very high frequency sounds. Do you live in a rural area with very little background noise? Do you wear earbuds often? Are you a construction worker listening to the constant sounds of engines and machinery? Our individual experiences and interactions with sound in our daily lives make our hearing capabilities unique to each of us.
Most marine mammals vocalize outside of the human hearing range. This is why we need so many displays — to see this “ultrasonic” sound. Each display provides specific information about these vocalizations, maps indicating the location of the sounds, and forms for recording additional data.
Listening to beaked whales from our “command center” reminds me of playing whack-a-mole. Our primary display consists of little dots, each representing a click, which scroll by telling us about the time and location of the animal that produced them. Clicking on each dot produces three diagnostic plots that provide more information, as seen below. These dots flash by and are typically visible for about one minute as new clicks continue to stream in.
There is still much to learn about species-specific characteristics of beaked whale vocalizations. This expedition is providing us data to add to a growing library of knowledge, ultimately with a goal of identifying beaked whale species based solely on the sounds they make. The recent Baird’s encounter was one such fortunate event where the whales dove within two to three football fields of us and stayed nearby, allowing us to capture thousands of clicks to study. A very rare treat!