Patterns of acoustical scattering in both depth and horizontal extent were analyzed to estimate the spatial and temporal scales of variability in biomass of mesopelagic sound scatterers, principally micronekton. The patterns observed included extensive layers of low and nearly uniform scattering strength and distinct three-dimensional patches of stronger scattering. These patches dispersed vertically at night after diel migration of a portion of the scatterers, but reassembled quite accurately the following day. Analysis of variance spectra for average acoustical scattering profiles within a patch suggest that micro-patches, with dimensions on the order of 15 m vertically by 1 km horizontally, are present both day and night. Horizontal variance spectra suggest the possibility of different horizontal aggregation mechanisms at scales above and below approximately 8.9 km.