Page 13 - Acoustics Today

Fig. 6. Acoustic recordings from the LEO-15 ocean observatory off Tuckerton, New Jersey showing nightly chorusing by sciaenids (weakfish and croaker) and cusk eels. The composite spectrogram shows the cusk eel sounds are at a higher frequency than the croakers, and peak in sound production at dusk and dawn. Temperatures on August 23 decreased due to an upwelling event, which was correlated with reduced levels of sound production.
because they allow profiling of the water column along with the ability to extend the spatial range of observations. The first study using underwater gliders to study fish sound produc- tion was published just this year (Wall et al., 2012). A Slocum glider was outfitted with a hydrophone and an internal acoustic recorder. The glider transited along a 135 km track in the Gulf of Mexico over the course of eight days. In this one short mission, suspected fish sounds from five species were mapped and their daily pattern of sound production was determined. Of these five sounds, four were previously unrecorded. One of the new sounds was a characteristic toad- fish boatwhistle, from the offshore leopard toadfish. The only previously verified fish sound was from the red grouper,
which had only been published in 2011 (Nelson et al., 2011). Gliders promise the ability to bring true shelf-scale ecosystem level mapping of the distribution of sound-pro- ducing fishes. One can envision gliders traveling entire con- tinental coastlines giving us the first detailed maps of the locations of spawning groupers, cods, and drums. With repeated transects and large scale acoustic networks, we will be able to monitor the movement and reproductive activities of fishes as they respond to climate change (See Figs. 7 and 8).
A sea of opportunity
Passive acoustic recording using underwater gliders demonstrates the promise of large-scale mapping of fish
Fig. 7. Platforms used for passive acoustic recordings. From left, a bottom mounted recorder showing a hydrophone on the top, mid-water recorders located on a PVC float, and a Slocum glider containing an integrated hydrophone and digital recorder (photo by C. Lembke).
12 Acoustics Today, July 2012