Gannon and Gannon: Passive acoustic assessment of soniferous fish density 
115 
Although they tend to yield coarse data, there are 
some potential advantages to passive acoustic methods 
(see reviews by Rountree et al., 2006; Gannon, 2008; 
and Luczkovich et al., 2008.). In comparison with tra- 
ditional fishery survey techniques (e.g., trawl surveys), 
passive acoustic surveys can be accomplished more 
quickly and cheaply with small vessels, few personnel, 
and low-cost equipment. Simple recording systems, such 
as the one used here, cost just a few hundred dollars 
and, in most cases, passive acoustic systems can be 
deployed with ease by one or two people in a small 
boat. Acoustic data loggers and telemetered sensors 
also allow remote data collection over long periods of 
time. Passive acoustic methods can allow the sampling 
of soniferous species that live on the bottom, within 
protective structures, or at great depths, and therefore, 
may be more appropriate than traditional sampling nets 
or active acoustic methods in some cases. Because of its 
relatively low cost, the ease with which it can be used, 
and its ability to collect data remotely from several sites 
simultaneously, passive acoustics allows larger areas 
to be monitored at higher sampling intensities than 
would be possible with a traditional survey method. 
Finally, passive acoustic methods are noninvasive and 
do not damage the habitat. Traditional fishery sampling 
techniques often cause high mortality rates of captured 
species and damage benthic habitat. Also, there has 
been much concern recently regarding anthropogenic 
noise in the sea (e.g., Popper et al., 2005, 2007); there- 
fore passive acoustics can be more desirable than active 
acoustics in some situations. 
Passive acoustics holds promise as a supplement to 
capture-based methods for assessing trends in relative 
abundance and for describing spatiotemporal patterns 
in distributions of soniferous fishes. To our knowledge, 
this is the first published attempt to compare passive 
acoustic data with data on the relative abundance of a 
soniferous fish species derived from traditional fisher- 
ies sampling techniques. Future research effort in fish 
passive acoustics should 1) help us to develop methods 
of quantifying calling rates with greater precision; 2) 
improve measurements of the contribution of the target 
species’ calls to the ambient sound; and 3) provide a 
better understanding of how the source levels of the 
calls of individual fish are affected by dissolved oxygen 
concentration, temperature, and body size. 
Acknowledgments 
We thank E. Horn, D. Waples, and many volunteers who 
assisted in the field. The U.S. Environmental Protection 
Agency (grant no. R261000-01-0 to L. Crowder and A. 
Read), Taylor Foundation, and Oak Fund provided fund- 
ing. This research was conducted under a collecting 
permit issued by the North Carolina Division of Marine 
Fisheries to the Duke University Marine Laboratory, 
and in compliance with the U.S. Animal Welfare Act 
under a protocol issued by Duke University’s Institu- 
tional Animal Care and Use Committee (protocol nos. 
A343-98-8, A418-99-08-2, A418-99-08-3, and A212-01- 
08). This article is contribution number 206 from the 
Bowdoin Scientific Station. 
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