Hydroacoustic Signal Classification of Fish Schools by Species

• Published in: Canadian Journal of Fisheries and Aquatic Sciences
• Main Authors: Rose, G. A., Leggett, W. C.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1988
• Subjects: Aquatic Science; Ecology, Evolution, Behavior and Systematics; Gadus morhua
• Online Access: http://dx.doi.org/10.1139/f88-073; http://www.nrcresearchpress.com/doi/pdf/10.1139/f88-073

Features extracted from hydroacoustic backscatter from fish schools enabled classification by species. Target species were cod (Gadus morhua), capelin (Mallotus villosus), and mackerel (Scomber scombrus), observed in the northern Gulf of St. Lawrence during 1985–86. Two features of internal school density (20 log R amplification) were the best discriminators. These were mean standardized peak to trough distance (SPT) and mean distance between voltage peaks (PP). Quadratic discriminant functions based on the variables SPT, PP, an inverse coefficient of variation, school depth, and off-bottom distance correctly classified 93% of schools (1986). These functions also correctly classified 93% of cod and capelin schools acoustically sampled independently during 1985. The target strength of individual fish was a less successful discriminator of species. For cod and capelin of known length, average target strength (TS) was a linear function of length: TS (decibels) = −65 + 20 log 10 length (centimetres). Mackerel had target strengths that were 8–12 dB less than those of cod of equivalent length. Quadratic discriminant functions based on target strength, school depth, and off-bottom distance correctly classified 77% of schools by species. Our methods are generalized to any schooling species or environment.