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 lowfrequency, 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 lowfrequency sounds, especially members of the families Sciaenidae, Gadidae, Ictaluridae, Cyprinidae, Batrachoididae, Haemulidae, Lutjanidae, and Serranidae. Passive acoustic methods include the use of lowfrequency 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 acousticsderived 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. Many fishery biologists are interested in following the movements and behavior of fishes by use of active ultrasonic acoustic tagging, in which fishes are rigged with an active acoustic tag that transmits its location to hydrophone receivers. The emerging field of passive acoustic methodology in fisheries surveys takes advantage of the fact that many species of fish naturally produce sounds and therefore possess natural acoustic tags. Passive acoustics utilizes low-frequency (,10 kHz) hydrophones to detect and monitor natural sound production by fishes, which is typically associated with feeding, aggressive encounters, courtship, or spawning behavior. Passive acoustics has a long history in fish biology, but it has only recently been applied to fisheries and their management (Rountree et al. 2006). Because most of these sounds are species specific, one can use a hydrophone to listen for sounds associated with specific behaviors. The temporal and spatial patterns of behaviors, such as spawning, can then be inferred simply by recording and analyzing the sounds using signal processing techniques. The use of passive acoustics as a modern tool for fishery investigations in a digital age suggests some interesting possibilities and questions. How many fishes are sound producers (i.e., already acoustically tagged)? There are more than 700 species known to produce sounds from at least 30 families (Fish and Mowbray 1970; Kaatz 2002; Johnston and Phillips 2003; Johnston and Vives 2003; Rountree et al. 2006), and many more soniferous fishes have yet to be recorded. Are these species harvested in commercial and recreational fisheries? Although the diversity of soniferous fishes is poorly understood, a partial list of sound producers that are caught recreationally or sold commercially would include members of Sciaenidae (Mok and Gilmore 1983; Johnson and Funicelli 1991; Saucier et al. 1992; Saucier and Baltz 1993; Luczkovich et al. 1999; Gilmore 2002; Roumillat and Brouwer 2004), Gadidae (Brawn 1961c; Hawkins et al. 1967; * Corresponding author: [email protected] Received November 19, 2006; accepted September 10, 2007 Published online April 3, 2008 533 Transactions of the American Fisheries Society 137:533–541, 2008 Copyright by the American Fisheries Society 2008 DOI: 10.1577/T06-258.1 [Article]