At the Pacific Islands Fisheries Science Center, the Cetacean Research Program uses a variety of passive acoustic approaches to advance its assessment capabilities and to examine the relationships between cetaceans and their environment. The use of passive acoustics to gather critical data and to augment visual surveys is growing more important. Passive acoustic data are used to augment ship-based line-transect surveys, to help delineate cetacean populations, to assess occurrence and seasonality, and to estimate the density, abundance, and trends of cetacean populations within the Pacific Islands Region.
Passive Acoustics for Population Assessment
Whales and dolphins spend most of their time under the surface of the water, where visual monitoring methods are ineffective. Additionally, sound travels much farther in water than light, and cetaceans commonly use sound rather than vision to communicate with each other and to find food. Using passive acoustic tools, we can listen to the sounds made by whales and dolphins, their ambient environment, and any human-generated noise. These data augment our visual surveys for cetaceans and provide an opportunity to examine temporal and spatial changes in the density and behavior of some species at time scales that we can not monitor using other methods. The data also provide insight into the acoustic environment, the soundscape, and changes within that environment that might affect cetacean populations.
Our passive acoustics program incorporates a broad diversity of instrumentation- bottom-mounted long-term acoustic recording devices, miniature recorders for use on mobile or dynamic platforms, drifting medium-term acoustic recording devices, towed hydrophone arrays during ship-transect surveys, and many novel approaches to addressing our challenging mission. Passive acoustics is particularly well-suited to helping us understand three important elements of population assessment:
- Species occurrence and range: What species occur in the area, how are they distributed, and when are they there?
- Population abundance and trends: How many animals are in the population? How does that abundance change over time?
- Population stresses: What natural processes or human-caused threats may be impacting the population? Are threats constant or does the severity vary? Can the threat be reduced?