Abstract

A two year time series of acoustic backscatter was acquired from the Middle Domain of the southeastern and central Bering Sea shelf starting in 2009. A three-frequency echosounder system was integrated into NOAA oceanographic moorings at these locations and provided information for the classification of backscatter into 4 biological categories: small (1-5mm), medium (5-15mm), and large (15-30mm) crustaceans, and resonant scatters. The seasonal pattern of backscatter intensity was tightly coupled to sea ice dynamics at both mooring sites, but the community structure and timing of zooplankton blooms differed between sites. Winter 2009 was a light ice year on the southeastern shelf compared to heavy ice presence in 2010. Comparison of backscatter intensity and structure between years at this location provides information about how sea ice extent impacts upper trophic level dynamics. Insights gained on the relationship between ice and community structure through analysis of acoustic backscatter between these two sites provides important information for predicting the ecosystem response in this area to variable and potentially decreasing seasonal ice extent associated with global climate change. [Work supported by ONR]

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