Joseph J. Luczkovich (Department of Biology and Institute for Coastal and Marine Resources) and Mark W. Sprague (Department of Physics)

East Carolina University
Greenville, NC 27858 USA

Recently, concerns have been raised about the decline in the population and spawning stock of some members of the drum family (Sciaenidae), especially the red drum, Sciaenops ocellatus. One management option that has been suggested is to create spawning reserves, but spawning areas must be surveyed first in order to protect them. Sciaenid fishes produce species-specific sounds associated with spawning and courtship. The goal of this study was to demonstrate that these sounds could be used to determine the locations of sciaenid spawning areas and the times in which spawning occurs. We measured spawning sounds in the Pamlico Sound (North Carolina, USA) using a hydrophone deployed off of a small boat and a network of autonomous sonobuoys to establish the location and time of spawning sounds for red drum, weakfish (Cynoscion regalis), spotted seatrout (Cynoscion nebulosus), and silver perch (Bairdiella chrysoura). At the same time, we captured and identified fertilized sciaenid eggs to establish where spawning occurred. We found a correlation between the presence of spawning-related sounds and spawning activity allowing us to use acoustic techniques to find spawning areas. These acoustic techniques are much less time and labor-intensive than egg and fish capture techniques. The U.S. Fish and Wildlife Service and the North Carolina Division of Marine Fisheries have used data from this passive acoustic habitat study to help formulate an essential habitat plan for North Carolina red drum.

During our passive acoustics habitat study, we discovered (with the help of Rountree and Mann) that the "chatter" sound previously identified as a weakfish was actually produced by the striped cusk-eel, Ophidion marginatum. We compared recordings of captive striped cusk-eels to field recordings of chatters and determined that they had the same waveform and spectral characteristics indicating that the were produced by the same species.

We are currently working on establishing other passive acoustic techniques to study spawning sciaenids. We would like to establish relationships between acoustic properties and the number of fish in a spawning aggregation and the size of an individual fish. We have been working with the National Undersea Research Center to use a remote operated vehicle (ROV) to obtain simultaneous underwater video and audio of spawning sciaenids to establish population densities and individual loudnesses.

During our essential habitat studies, we noticed an interesting phenomenon: silver perch would suddenly become quiet when we heard bottlenose dolphin, Tursiops truncatus, signature whistles. We hypothesized that there was an acoustic interaction between the bottlenose dolphin and the silver perch. Silver perch compose a large part of the bottlenose dolphin diet in North Carolina waters. Furthermore, it is well known that a majority of bottlenose dolphin diet consists of soniferous fishes. Could the silver perch be reacting to the sound produced by bottlenose dolphin predators? The answer is yes. We performed experiments on silver perch aggregations and found that they did become quiet when we played bottlenose dolphin signatsure whistles.

We are also interested in acoustic competition between fish species. Is there acoustic competition for bandwidth between soniferous fish? Does acoustic competition play a role in habitat selection? These are some questions that we are currently trying to answer.

Sciaenid fishes produce sound by driving their swimbladders with drumming muscles. We are interested in modeling this process so that we can establish a relationship between fish size and the sound produced. Others have established relationships between fish size and swimbladder size. Hence, we should be able to determine a fish size-waveform relationship by relating waveform properties to swimbladder dimensions. Mark Sprague modeled the weakfish sound production system as a driven, highly-damped oscillator and demonstrated that such a system has a relationship between waveform properties and swimbladder dimensions. We would like to experimentally confirm this model and establish a waveform-size relationship for weakfish and other species.

Mid-ocean coral reefs are often distant from ports where agencies charged with monitoring their health are based. Such distant reefs are difficult to monitor regularly using boats and field crews. However, many reef organisms including fish, mammals, and invertebrates produce unique sounds, which can be monitored remotely as an indicator of reef activity. We are working with the Honolulu Laboratory of the National Marine Fisheries Service to develop passive acoustic monitoring techniques for coral reefs and devices that can be deployed on reefs for remote monitoring purposes.