Report from Louisville ASA meeting

I spent the better part of last week at an Acoustical Society conference in Louisville, Kentucky. I am glad that the conference was interesting because as cities go, Louisville isn’t. (Having a museum of baseball bats as a major cultural venue about sums it up. Oh, and then there are the many Bourbon attractions…).

Louisville is also not a big hot-spot for Marine Mammology, so the Animal Bioacoustics sessions – which at the Acoustical Society are usually dominated by papers on whales and dolphins, were liberally peppered with papers on lemurs, bats, frogs, and arthropods. There was an entire session mostly dedicated to bat work from Rolf Müller’s lab at Virginia Tech – which included “bat robots” – biomimetic versions of the functional leaf-noses and morphing pinnae (ear shells) of horseshoe bats. Synchronized motions of the nose in projecting sound, and the ears in receiving sound allow these bats to distinguish fine details in their targets high speeds.

In the “bio-inspired, biomimetic” session there was a discussion on how most animals sense “acoustic flow” instead of “sound pressure” with a paper examining how spider webs might be used to convert acoustically-induced air motion into electrical energy. “Acoustic flow” – also called “particle motion,” is the dominant hearing mechanism for marine animals because as any diver knows, underwater pressure is directly correlated with depth, so having extremely sensitive pressure sensors (as we terrestrial animals do) would be an impediment to detailed underwater sound perception.

I presented two papers. The first one was on policy: “Best available science? Are NOAA Fisheries marine mammal noise exposure guidelines up to date?” This includes a preamble on  the history of noise regulations pursuant to the Marne Mammal Protection Act. The “lay” version of the paper is brief (and perhaps interesting to non-policy wonks). The genesis of the paper orbits around how and why the agency whose practical remit is to include “the best available science” in their regulations, is more than a decade behind the vanguard of scientific understanding.

The second paper examined “Evidence of synchronous  chorusing  in  North  Atlantic  minke  whales  (Balaenoptera  acutorostrata)” which examines a recording provided by Denise Reisch, who at the time of the recording was working at Cornell University’s Stellwagen Banks Hydrophone array. While my hypothesis is just speculative, what the recording seems to reveal (to me, anyway) is a single minke pulsing away, and about half-way through a second one joins and they immediately “entrain” just as crickets do. Doing a bit of math – looking at their “inter-pulse interval” and the differential intervals between the calls, I can place the two whale’s locations relative to the hydrophone.

If this hypothesis is correct, it would shed light on potential behavioral disruptions that mechanical equipment pulsing (like airgun surveys) may have on the behavior of these animals. But in order to verify the behavior, we will need two hydrophones to confirm the differential locations of the callers, which is one of the objectives of our Farallones Hydrophone project.

So while the conference topics and papers may seem like a lark, understanding how animals interact with their surroundings through sound – whether through convoluting ears and noses, or through chorusing and acoustic communities, may give us ideas on how to be better aquatic neighbors.