Many fishes make sounds. This fact allows our Fish Acoustics Research Team (comprised of Associate Professor Mark Sprague in Physics, Professor Hal J. Daniel III, former and current graduate students Stephen Johnson, Chris Pullinger, Todd Jenkins, Marcie Hutchinson, and Cecilia Krahforst) to use the passive acoustic approach to determine spawning areas used by fishes in the family Sciaenidae (drums, weakfish, and seatrouts), which are both commercially and recreationally valuable in North Carolina. These fishes make species-specific sounds using their swim bladders and sonic muscles during spawning activities; in most cases, males make the sounds as an advertisement call to attract females. By recording sounds of captive specimens of each of five species (silver perch, Bairdiella chrysoura, weakfish, Cynoscion regalis, spotted seatrout, C. nebulosus, Atlantic croaker, Micropogonias undulatus, and red drum, Sciaenops ocellatus), my colleagues and I are able to identify the species making calls by simply by listening. We listen to fish sounds, analyze their spectral properties, correlate the sounds with plankton net, trawl and gill net samples, and produce spawning area maps for each species. Our team discovered that silver perch became acoustically inactive when bottlenose dolphins (Tursiops truncatus) were in the spawning areas indicating that these fishes are able to hear and respond to a predator’s sounds. A common sound heard in Pamlico Sound is called “the chatter”; previous researchers had identified it as being produced weakfish, but our team determined that it was produced instead by striped cusk-eels (Ophididon marginatum). A study using an ROV was conducted at one of the spawning areas in the Ocracoke Inlet; this ROV was fitted with a calibrated hydrophone and was positioned near a calling silver perch, allowing for a sound source level measurement . An analysis of an autonomous sonobuoy survey of Pamlico Sound was recently accepted for publication in the Transactions of the American Fisheries Society (Luczkovich et al. 2008).
Food Web Network Models
In food web network modeling, a matrix of food web interactions (who eats whom) is used to describe the flow of energy, carbon, or other materials through a series of species or compartments in an ecosystem. Flow rates are based on dietary data, production rate, consumption rate, and respiration rate estimates. These network models, when applied to marine food webs, offer quantitative perspectives of the entire ecosystem. I have been working in collaboration with biologists, sociologists, anthropologists, and mathematical modelers (Dan Baird of Stellenbosch University in South Africa, Steve Borgatti at University of Kentucky, Robert Christian of ECU Biology Department, Jeffrey C. Johnson of ECU Sociology Department and the Institute for Coastal Science and Policy, and Martin Everett of the University of Westminster in England, Lisa Clough of ECU Biology, David Griffith of ECU Anthropology and the Institute for Coastal Science and Policy, and Brian Cheuvront, NC Division of Marine Fisheries) to describe both food web interactions in marine ecosystems and interactions in human social systems. These models can be used to study the effective trophic levels (between integer levels) of any group of organisms, the cycling of nutrients, the description of the extended diets of individual species (i.e., what prey they consume and depend upon indirectly), and prediction of their trophic impacts on other species. Trophic network models have been constructed for a seagrass ecosystem at St. Marks, Florida (Luczkovich et al. 2003), a coral reef ecosystem at Calabash Caye, Belize (Deehr et al. 2008) and an estuarine ecosystem inside and outside of closed trawling areas in Core Sound (work in progress, Johnson, Luczkovich, Clough, Griffith, Cheuvront, Hart and Deehr). Graduate and undergraduate students are involved in data gathering to parameterize these models (Rebecca Deehr, Deirdre Barry, David Chagaris, David Gloeckner, Kevin Hart, Molly Fitzpatrick, Kyle Regensberg, Garcy Ward). Finally, the trophic role (or niche) of any species can now be measured and their position in the food web visualized using MAGE 3D modeling software, allowing one to view and explore the complex interactions of such food webs (Luczkovich et al. 2003). These network modeling approaches can now be applied to characterize food webs at various time scales and in diverse ecosystems. Currently, my collaborators and I are working to make these models represent a temporal sequence of trophic network development using continuous time Markov chains (Johnson, Borgatti and Luczkovich, accepted). We have received much attention for our work in this area. One of these papers (Luczkovich et al. 2003) was awarded the 2006 Helms Award from the Sigma Xi Research Society at ECU. In the future, human interactions and human social systems can be included as part of these food web network models, and we hope to be able to predict the impact of humans on ecosystems.