Passive acoustics as a tool in fisheries science

Many fishery biologists that are interested in documenting fish habitat and following the movements and behavior of fishes use acoustic tags. Because over 700 fish species naturally produce low-frequency, species-specific sounds, these can be used as natural acoustic tags. Passive acoustic approaches (monitoring sound-producing fishes with hydrophones) show great promise for gathering data in a noninvasive and continuous manner. In this special section, authors review past studies and contribute new findings based on the concept of passive acoustics, in which the sounds produced by fish are used to identify the species present and quantify their relative abundance. Fish have long been known to produce low-frequency sounds, especially members of the families Sciaenidae, Gadidae, Ictaluridae, Cyprinidae, Batrachoididae, Haemulidae, Lutjanidac, and Serranidae. Passive acoustic methods include the use of low-frequency hydrophones, digital recorders, autonomous recording sonobuoys and data loggers, and towed hydrophone arrays to record fish sounds. The sounds of fishes that have been recorded so far have been described in monographs, scientific papers, and online digital libraries; in most cases, the recordings are species specific and can be used to identify fish. Work is progressing in using the passive acoustic approach along with traditional fisheries sampling methods (net and active acoustic surveys) to identify habitat use, spawning areas, and relative abundances. The authors in this special section present new passive acoustics-derived data on sciaenids, batrachoidids, and ictalurids. They outline the methods currently being used and discuss their limitations, provide examples where passive acoustics has been employed successfully, warn of pitfalls in interpreting acoustic data, and lay the groundwork for future studies.