Abstract
Echo-signals were collected with a 38-kHz transducer across frontal zones and shelf-break features off the south-east coast of South Africa, with the objectives of (a) developing a method for automatically characterizing biological patterns at appropriate spatial scales and (b) quantifying the extent, intensity, structure and identity of patches by analysis of their acoustic signal. Patches were identified and isolated according to interactive criteria based on intensity thresholds of the signal and continuity of the echoes above and below those thresholds. Statistical analysis indicated that the dispersion patterns of organisms within and between patches, and patch size and shape, explained most of the observed variability. Patchiness was more intense where frontal gradients were strongest. The technique gave good separation between zooplankton and fish aggregations and it should prove beneficial for small-scale distributional studies offish and their prey.
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