Acoustic estimates of zooplankton and micronekton biomass using an ADCP

Abstract

A calibrated 153-kHz narrow-band ADCP (Acoustic Doppler Current Profiler) has been used to collect acoustic backscatter intensity (Sv) data during several cruises in the Gulf of Mexico. Data have been gathered both while on station and while underway along transects through different hydrographic regimes, enabling an examination of both temporal and spatial trends in backscatter. In addition, zooplankton and micronekton stocks were intensively sampled with a 1 m2̂ MOCNESS (Multiple Opening-Closing Net Environmental Sensing System). Empirical correlations between spatial and temporal variations in Sv and in standing stocks of zooplankton/micronekton will be presented. Sv measured with an ADCP may be useful as an index of zooplankton and micronekton biomass. The location and abundance of these food stocks are hypothesized to be important in determining the distribution and abundance of marine cetaceans in the Gulf of Mexico. In addition, Sv-derived estimates of such stocks may allow inferences about secondary biological productivity in the Gulf, and the role that mesoscale circulation features might play in driving large-scale patterns. [This ongoing research is supported by the USGS Biological Resources Division and the US Minerals Management Service under USGS BRD Contract No. 1445-C109-96-004. For more information, see http://www.tamug.tamu.edu/gulfcet.]