Zooplankton sound scattering layers in north Norwegian fjords: Specifications and functioning of the acoustical, data- and net-sampling systems

Abstract
The specifications and functioning of the acoustic, data and environmental monitoring systems used in the ‘Zooplankton Sound Scattering Layers Project’ of the University of Tromsö are described. The instrumentation onboard RV ‘Johan Ruud’ for studying sound scattering layers includes 38 and 120 kHz echosounders, a digital echointegrator, a computer (for data storage, retrieval, and analyses — including echointegration, and conductivity, temperature, oxygen, and depth-sonde analyses), fluorometer, irradiance meters, pelagic and prawn trawls, a Longhurst-Hardy Plankton Recorder, and a Tucker trawl. Various advantages and limitations as well as possible future development of the systems are discussed with respect to zoo-plankton-orientated research on sound scattering layers.