The ocean is full of sound – from snapping shrimp, to fishes to whales, nearly everyone underwater is talking with one another.   Acoustic communication is particularly important for whales and dolphins, as sound travels much further underwater than light, and different species use sounds to coordinate foraging activity, mating, or other social interactions.

In 2013, we discovered that Omura's whales produce low-frequency, pulsive sounds, at least some of which seem to be used as a breeding display!  So we have been conducting a study using acoustic recorders to learn more about the presence and distribution of Omura's whales around the northwest of Madagascar. 

In December 2015 we placed four underwater microphones (hydrophones) at various sites around our study area. Each of these hydrophones recorded all underwater noises, or the “soundscape” for the past 12 months. 

Sal and Loic just did a dive to 35m to recover our recorder. It's got a little bit of growth on it, but otherwise looks good!

In the last couple of weeks, we've been diving at each of the sites to recover the recorders, and we're glad to report that we got them all back!!  This is actually great news, because it is not always guaranteed that you will find and recover remotely deployed instruments like this.  As an oceanographer once told me as a student, when you put something over the side of your boat and into the ocean, be prepared to kiss it good-bye, and feel lucky if you get it back….!

The next step is to download all the data, and then we'll spend the next few months combing through the recordings, looking for Omura's whales vocalizations and other species who are also in the area.  These data will help us to understand the seasonal habitat use of Omura's whales in Madagascar.

Sal and Boris looking over the first of the acoustic data they just downloaded!

An example of the new acoustic data, showing the songs of multiple Omura's whales.  You read this like you would sheet music - time is across the x-axis and frequency (or pitch) on the y-axis.  The data look clean and beautiful!

Before we leave the field this season, the recorders will be redeployed to record over the next year, this time in deep water off the shelf of Madagascar. Can't wait to see what we find!