Listening to fish sounds in the Amazon
A new field of passive acoustics is rapidly emerging in marine and aquatic ecology, in which scientists use underwater technology to listen in on the noisy aquatic realm.
Listen to freshwater drum sounds (note, an aquatic insect can be heard in the background)
Passive acoustics is distinguished from other types of bioacoustics, because it uses naturally occurring sounds to gather information on fishes and other aquatic organisms (ie listening), rather than using artificially generated sounds (eg sonar).
Passive acoustics provides a number of important benefits for ecological research. First, it can be used to find and monitor fishes (and other animals) that produce sound. By examining spatial and temporal trends in sound production we can determine spatial and temporal patterns of species occurrence and activity patterns. In cases where sound production is associated with spawning, we can infer essential fish habitat locations based on recordings of spawning and courtship sounds. Even for non-vocal fishes, sounds made during feeding can sometimes be used to determine daily feeding activity patterns.
Passive acoustics is a powerful new tool to monitor diversity of aquatic organism
Passive acoustics can also be used to simultaneously monitor sources of noise pollution, and to study the impact of humans’ activities on aquatic communities. Anthropogenic sources include noise generated by boating activity, seismic surveys, pile drivers, automobile traffic, sonar, fish finders, depth-finders, drilling for oil and gas, and military activities.
The importance of anthropogenic noise and its effects on marine mammals is widely known, but has only recently begun to be acknowledged and studied for fishes and invertebrates. Thus, scientists are increasingly calling for research to characterise the underwater soundscape of marine and freshwater habitats around the world.
One of the biggest obstacles in the advancement of these studies is a general lack of data on soundscape components. That is, reference libraries of authenticated underwater sounds produced by aquatic animals are unavailable for many, if not most, systems. How can you study anthropogenic noise impacts on aquatic ecology if you don’t know what species make sound, never mind when, where and why they make them! (More information here)
This year Operation Wallacea will launch a new research initiative to begin documentation of the Amazon River Soundscape as part of its Peru Expedition. The project will provide baseline data to aid future researchers wishing to use passive acoustics methods in studies of the Amazon River ecosystem.
Just as ornithologists have used bird call surveys for decades to monitor bird diversity, passive acoustics is a powerful new tool to monitor diversity of aquatic organism. However, in order to use passive acoustics as an effective survey too, scientists need to develop libraries of known sounds to use as references for species identification.
The Amazon Soundscape survey will begin to catalogue biological sounds from known and unknown sources in the Amazon River. Important known fish sound producers in the Amazon include piranhas, catfishes, and cichlids.
However, because so little is known of the soundscape of the Amazon River system, it is expected that the vast majority of sounds to be catalogued will be new to science. Therefore, significant efforts will be made to identify unknown sounds through observation and sound auditioning projects.
Capturing the fish
Fishes will be captured by hook-and-line and other methods (traps, nets) for auditioning experiments. Potential soniferous activity will be monitored during capture to document disturbance calls. In addition, fishes will be held for short periods in water filled coolers, small wading pools or floating pens to monitor them for potential sound production. Most fishes will be returned to the water alive; however a few specimens for which validated sound recording were obtained will be preserved to serve as museum voucher specimens.
Although the Amazon Soundscape project will initially focus primarily on fishes, data on both aerial and underwater sounds will be collected to fully characterise the soundscape and the relationship between above water and below water sounds. In addition, sounds of river dolphin, manatee and other aquatic and semi-aquatic mammals, together with those of caimans and other reptiles, amphibians and aquatic insects will be documented as time permits.
Passive acoustics will be especially valuable in enhancing the river dolphin survey and in documenting the role of fish sound production on dolphin prey selection. That is, we suspect that river dolphin key in on vocal fish prey just as some marine species have been found to do.
The Amazon Soundscape project will constitute the first large-scale, systematic survey of fish sound production in South America and promises to open up an exciting new realm of research in tropical ecology.