Acoustic characterization of pelagic fish distribution across the South Pacific Ocean

Abstract

Acoustic data can provide quantitative and qualitative information about the distribution and abundance of mid-trophic level functional groups in the marine ecosystem. Acoustic data, opportunistically collected on 2 return voyages between New Zealand and Chile, were used to describe the distribution patterns of pelagic fishes across the South Pacific Ocean. The area backscattering coefficient (sa in m2 m-2) at 38 kHz in the upper 600 m was used as the measure of fish abundance, and was assumed to be dominated by mesopelagic fishes. Consistent vertical and horizontal patterns of pelagic fish distribution were identified. Vertical (depth) patterns included diel migration and layering. Key horizontal (spatial) patterns were coastal intensification and oceanic patchiness. Boosted regression trees models were used to explain the relationship be - tween sa and environmental and geographical variables. The key finding was that there was a strong correlation between satellite-derived chl a and distribution of acoustic backscatter. The incorporation of species composition information from biological sampling would improve the relevance of the results of this study. Nevertheless, these large-scale estimates provide an opportunity to validate model predictions of mid-trophic functional groups and to inform ecosystem-based fisheries management. © Inter-Research 2013.