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My current research activities integrate three distinct but related areas: scale-dependent processes influencing aquatic organism distributions, predator-prey interactions, and the application of acoustics to aquatic ecology and resource management
Scale-Dependant Processes Influencing Aquatic Organism Distributions
In aquatic ecosystems, spatial and temporal patchiness is a well-recognized attribute of organism distributions. Despite numerous techniques used to describe distributions, few tools quantify the relative importance of biological and physical processes that influence distributional variance. Rate diagrams, dimensionless ratios of rates plotted as a function of spatial and temporal scale, show that the relative importance of growth, recruitment, mortality, passive flux, and locomotory flux are strongly dependent on temporal and spatial scales of observation. This technique provides a common currency to compare variance-generating processes in any environment over a wide range of spatial and temporal scales.
The second research theme uses spectral analysis and bioenergetic models to examine how spatial and temporal variability in temperature, prey size, and prey abundance influences distributions and growth of mobile predators and their prey. Spatial variance of mobile aquatic organisms does not follow the inverse square law proposed for aggregation scales of passive tracers such as plankton. Numeric experiments show that biological processes such as shoaling and schooling influence the rate of change in distributional spatial variance.
Bioenergetic models use a mass balance approach where energy gained by consumption is partitioned into growth, metabolism and waste. One application of bioenergetic models integrates temperature and prey distribution data in spatially explicit maps of potential predator growth. Maps of predator growth can then be used to quantify the suitability of an area or volume as habitat for a particular fish species. Predator access to prey may be restricted by environmental conditions and result in decreased growth. Bioenergetic models and environmental data can be integrated for any predator-prey pair in any ecosystem of interest. To illustrate by example, one project combines predator-prey spatial interactions with bioenergetics and acoustics.
Application of Acoustics to Aquatic Ecology and Resource Management
Fish distribution and abundance data collected for these programs are sampled using scientific echosounders. We are comparing predictions from morphologically based acoustic models to laboratory and field measurements in an effort to better understand variability in scattering of sound by aquatic organisms. Digitized radiographs of fish bodies and swimbladders are combined with Kirchhoff-ray mode backscatter models to predict echo amplitude as a function of fish species, length, aspect, roll, and acoustic wavelength. Predictions from backscatter models have been used to investigate the choice of carrier frequency for echosounders, identify constraints of size-based abundance estimates using the inverse approach, quantify the effect of digital image resolution on breadth of backscatter resonance peak and backscatter amplitude, examine effects of acoustic size choice on accuracy of fish population abundance estimates, and to quantify potential species discrimination based on signal-to-noise backscatter amplitudes. All research in this area contributes to the acoustic identification of fish species.