Experimental hydroacoustic estimation of rockfish (Sebastes spp.) biomass off Vancouver Island, November 13-25, 1991 / by R. Kieser, K. Cooke, R.D. Stanley, and G.E. Gillespie. : Fs97-4/2185E-PDF

"The precision of acoustic biomass estimates of rockfish (Sebastes spp.) was examined on the continental shelf off Nootka Sound, British Columbia. We assessed the differences between day and night biomass estimates from areas of about 250, 110, and 30 km² and examined the variability among estimates from several passes on two tracklines. School structure, distribution, and behaviour of S. flavidus was examined acoustically. The species distribution was restricted bathymetrically and its areal extent was governed by bottom slope and topographic features. Diurnal distributions were characterized by dense, vertically stacked schools. Nocturnal distributions showed much more diffuse aggregations, both near bottom and in the midwater. Transitional behaviour occurred very rapidly at twilight. The normal pattern was one of dispersal of diurnal schools in both horizontal and vertical directions at dusk and the subsequent regrouping of nocturnal aggregations at dawn, nearer the bottom"--Abstract, page iii.

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