Volume 8, Issue 3, July 2012
Index of content:
8(2012); http://dx.doi.org/10.1121/1.4753916View Description Hide Description
Lower a hydrophone into nearly any coastal area at dusk or night and you will be immersed in a world of clicks, knocks, and hums. After several seconds of listening and internally classifying sounds, you'll want to ask, “What made that sound?” While we are mostly familiar with the communication and echolocation sounds of marine mammals, thousands of other animals produce sound. Fishes are likely the largest source of biological sound in the coastal oceans. Partly this is due to some species being very loud, and partly this is due to their being so many fish producing sound.
8(2012); http://dx.doi.org/10.1121/1.4753913View Description Hide Description
Many animal taxa—birds, frogs, and some mammals—conspicuously advertise their presence, identity, and behavioral status through vocalizations. In many environments, these species are more readily heard than seen. Accordingly, many bird and frog surveys obtain most of their data by listening rather than looking. Dramatic improvements in audio recorder technology have created compelling opportunities to make long duration environmental recordings with compact packages. This technology extends the spatial scope and temporal extent of acoustical monitoring and provides archival records of ecological conditions. Birdsong research experienced dramatic growth as recording and spectrogram analysis technology became practical. Based on a sample of recent publications, environmental science may be on the cusp of similar growth in autonomous acoustical monitoring.
8(2012); http://dx.doi.org/10.1121/1.4753914View Description Hide Description
The first recorded incident of active acoustic detection of biological organisms (that the author is aware of) was in the “deep scattering layer” (DSL). Early depth measuring systems used paper‐charts to record the strength of the echoes that were detected. The seafloor produced a very strong echo, however the chartrecorder also showed weaker reflections occurring several hundred meters deep in the ocean that were definitely not the seafloor. The cause of the DSL was correctly hypothesized to be biological in origin, but it was not until the first submersible traveled to these depths that the specific sources (small fish and zooplankton) were identified. If you are trying to create bathymetric maps using acoustic methods, non‐seafloor reflections (like the DSL) are noise or unwanted signals. However, as many people have said, one person's noise can be another person's signal. Those of us who are interested in the biological organisms in the ocean have found this “noise” to be one of the best methods possible to study these animals in their natural habitat.
8(2012); http://dx.doi.org/10.1121/1.4753915View Description Hide Description
One of the most fundamental questions we can ask about a wildlife population is “How many are there?” Estimates of population size, or a related quantity population density (i.e., animals per unit area), are crucial for effective management, whether the management goal is conservation of a threatened or endangered species, control of a pest species, or optimal harvest of a species used for food. Population estimates are used to prioritize species of conservation concern, to monitor the success of management programs, and to set limits on harvest or incidental bycatch. Although “how many?” is a simple question to ask, it is often a hard one to answer, given that many populations are patchily distributed over very large areas and their lifestyle can make them quite cryptic to human observers. In this article, we introduce an emerging field with great potential—the estimation of wild animal population size and density using passive acoustics.