Spatiotemporal patterns of near-surface acoustic backscattering in the eastern Bering Sea based on multifrequency analysis and geostatistical methods

No abstracts are to be cited without prior reference to the author.

Fisheries acoustic surveys often collect multifrequency data to help classify the species composition according to the echo sign. Because fish are usually the primary target species, relatively little effort is spent on confirming the identity of the other scatterers. However, methods to characterize the spatio-temporal patterns of these other scatterers based solely on acoustic data may provide important insights into understanding ecological relationships among these assemblages and those of the target species. Here, we conduct an analysis of multifrequency acoustic data collected in the eastern Bering Sea (EBS) during the summers of 2004, 2006–2008 to describe the spatio-temporal characteristics of a persistent, near-surface acoustic backscattering layer that exists throughout most of the EBS during summer. Analysis methods include unsupervised clustering, which takes into account the spatial context of these data. Our approach initially focuses on the large-scale patterns in the frequency response, and then integrates small-scale patterns (i.e. echogram morphology) by using selected variogram-based textural indices. Categorical maps of each identified class of scatterers are produced and significant changes in their spatial patterns are tracked over time. Results will be used to optimize a field sampling plan to identify the species composition of this unique large-scale, near-surface feature as well as to identify important biophysical forcing mechanisms that influence its spatial distribution and abundance.