Acoustic measurements of the geometric dimensions and packing density of herring (Clupea harengus), sprat (Spraltus sprattus) and saithe (Pollachius virens) schools were conducted by multi-beam sonars and echo integrator systems. Relationships between the backscattered echo energy, the estimated school biomass and the school dimensions were quite similar for the three species and independent of the fish size. Seasonal and regional differences in schooling behaviour of herring were detected. School-dimension to schoolbiomass conversion may be a useful method for abundance estimation of pelagic species, and also for biomass measurements in fisheries.
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Misund et al. (1992) studied this question.