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Results are presented from research on the relationship between the biological organisms present at the Gulf Stream boundary near Cape Hatteras and the physical properties of the frontal zone such as thermal gradient, salinity, light, and primary production. The authors studied marine animals >or=1 cm to depths of 150 m. The populations of organisms were typically heterogeneous, i.e. mixtures of fish, arthropods, cephalopods, and soft-bodied animals. The purpose was to examine the robustness of the general models for acoustic scattering that are based on scattering from species not part of this study. Single-frequency single-beam sonar was used to detect and classify the animals. Size frequency distribution of the various animal types from trawl data was used as input into the scattering models to produce a predicted value of the acoustic volume scattering length. The field sonar data were examined for potential problems in comparing trawl and sonar data. The comparison between the predicted and field-measured values demonstrates the potential usefulness of the general models in areas with different taxonomic assemblages. Most data was found to lie within 5 dB of the predictions with some data systematically outside the 5-dB bars.