Seasonal Variability in Gulf of Maine Zooplankton Acoustic Material Properties

Gareth Lawson, Biology
Peter Wiebe, Biology
Serdar Sakinan, Biology

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Abstract

Studies of zooplankton ecology and assessment surveys underpinning ecosystem-based approaches to fisheries management share a common need for effective methods for quantifying zooplankton abundance and distribution.  Active acoustic methods provide a powerful means of characterizing zooplankton at high resolution across spatial and temporal scales, but accurate interpretation of acoustic data requires proper parameterization of the scattering models needed to estimate the target strength, or expected acoustic return, from individual animals.  In particular, small errors in the parameters describing an animal’s acoustic material properties (i.e., sound speed and density contrasts) can lead to an order of magnitude uncertainty in estimates of animal abundance.  Here we propose to examine seasonal and depth-related variability in the acoustic material properties of two key species of zooplankton in the greater Gulf of Maine region, Meganyctiphanes norvegica and Calanus finmarchicus, and to assess the improvements in scattering model predictions via comparison of net samples to in situ acoustic observations.  These measurements are key needs in ongoing efforts to understand zooplankton distribution based on regional acoustic data streams, including autonomous acoustic systems on the OOI Pioneer Array, the new broadband echosounder on the R/V Neil Armstrong, as well as multifrequency acoustic data collected incidental to NOAA zooplankton surveys.