A 200 kHz echosounder modified to sample directly into a computer was used to survey the mesopelagic boundary community (MBC) in waters off the leeward coasts of three Hawaiian Islands from dusk to dawn. The target strengths of individual mesopelagic organisms captured in Isaacs-Kidd midwater trawls were measured with the echosounder in a shipboard seawater tank for use in echo-energy integration calculations. Acoustic survey data were mapped in ArcView, allowing analysis of spatial structure. The MBC is spatially heterogeneous both horizontally and vertically. The parameters of patch structure vary significantly throughout a night and between islands. The density of mesopelagic organisms was consistently higher off the coasts of Oahu and Lanai than the coast of Hawaii. However, the density of organisms observed in all locations was high, reaching a maximum of 1800 organisms/m3 off Oahu and 700 organisms/m3 off Hawaii. Patterns in density were significantly affected by the location’s distance from the shoreline, but not by its depth. Patterns in density suggest that the MBC undergoes a significant diel horizontal migration in addition to its well-documented vertical migration. Due to this predictable and conserved horizontal migration, the MBC is found much closer to shore than previously reported.