Acoustic and optic characterization of forage fish distribution in the Bering Sea

Abstract

Mesopelagic forage fish species are important components of the Bering Sea ecosystem, but information on species distribution and identity is limited. Using acoustics and optics [LIght Detection And Ranging (LIDAR)], this study compared distribution patterns detected by the two gears. Forage species distribution and quantity differed between shelf (6–100 m) and slope (6–100 m, 100–300 m, 300 m to bottom) regions. Acoustic results suggested that shallow and deep depth zones contained dispersed backscatter while the middle slope layer contained patchy schools associated with the shelf break. Variogram results for repeated LIDAR surveys of the shelf and slope regions indicated that backscatter distribution between 6 and 30 m was dynamic at the scale of days. This result was expected given the strong frontal nature of the area. When LIDAR results were compared with coincident acoustic transects on the shelf and slope, differences were found in gear detection of backscatter. Based on acoustic results, 25%–63% of forage fish in the shelf and slope regions were deeper than the LIDAR detection range. Although both LIDAR and acoustics are constrained to portions of the water column, the utility of remote sampling technologies is dependent on survey objectives. [Funding was provided by the North Pacific Research Board.]