Progress in in situ and vessel-mounted acoustic Doppler current profilers to measure zooplankton abundance.

Abstract

Acoustic Doppler current profilers (ADCPs) offer a unique ability for studying biological structures in the ocean over a wide range of time and space scales. Studies of the capabilities of RD Instruments’ ADCPs operating at 307 and 150 kHz have been carried out to measure zooplankton abundance. A pilot study indicated that the method held great promise with an accuracy of about ±20% (Flagg and Smith, 1989). However, questions remained on the effects of differences in size class distribution and the use of ADCPs in noisier shipboard environments. Since then, long term insitu and shipboard ADCP results with simultaneous net data have been collected. The results show (1) that the ADCP’s ability to detect zooplankton density fluctuations to an accuracy of ±10% to 20% is confirmed, (2) that size class distribution fluctuations do not seem to have a major effect, and (3) that the quality and hence the range of the shipboard data is a strong function of ship speed and sea state. Dealing with shipboard data has proven difficult. Meaningful results are limited to regimes with very favorable signal-to-noise ratios.