Kristin Brooke Hodge
Research Analyst, Bioacoustics Research Program, Cornell University
Over the past few weeks, we have surveyed the South Taranaki Bight, New Zealand, collecting biological and oceanographic data to learn more about the population of blue whales in this region. Our efforts have been successful: we have encountered multiple blue whales, and recorded information about their identification, behavior, and habitat. While our visual survey efforts have provided us with an invaluable dataset, our field season is shortly coming to an end. So how can we continue to learn more about the blue whale population, if we cannot collect visual survey data?
Solution: we will study the sounds they make.
Bioacoustics is a non-invasive method to study acoustically-active animal populations in terrestrial and marine habitats. Scientists can eavesdrop on animals by recording and analyzing their sounds, and in turn gain insights about their occurrence, behavior, and movement patterns. This is especially useful for studying elusive or rare species, such as the blue whale, that can be difficult to find in the field. Since blue whales produce high intensity, infrasonic calls and songs that can travel for many miles across ocean basins, we can capture information regarding their spatial and temporal occurrence, even if we cannot see them. (To listen to a blue whale call recorded off of Chile click here.)
We are using Marine Autonomous Recording Units (MARUs), developed by the Cornell Bioacoustics Research Program, to record blue whales (Fig. 1). The MARU is a digital audio recording system contained in a buoyant sphere, which is deployed on the bottom of the ocean using an anchor. Each MARU has a hydrophone that collects acoustic data, and these sounds are recorded and stored on electronic storage media inside the MARU. The MARUs are programmed to record continuous, low-frequency sounds for approximately six months, after which they pop up to the surface of the ocean, ready to be retrieved for data analysis and redeployed with fresh batteries and storage media.
Over the course of this field season, we strategically deployed five MARUs across the South Taranaki Bight (Fig. 2), and we will record acoustic data in these five sites over the next couple of years. This will allow us to understand patterns of occurrence at larger spatial and temporal scales than we can accomplish with visual survey alone. Our acoustic dataset will complement the biological and oceanographic data we collected on survey, providing a more complete picture of the blue whale population in the bight.
To see us deploy a MARU in New Zealand, check out this video: