Autonomous surface vehicles for persistent acoustic monitoring of zooplankton in a highly productive shelf area

Observations of spatial and temporal distribution of low and mid trophic level organisms traditionally rely on ship-based measurements. The integration of fisheries research echosounders on surface and sub-surface unmanned vehicles change this situation and facilitate persistent monitoring of these trophic levels. Additionally, concurrent observations by surface and subsurface vehicles with appropriate sensors facilitate measurements of physical and biological processes at appropriate spatial and temporal scales, needed in order to sufficiently resolve the connected variability of physical and biological processes in the oceans. The GLIDER project implements this approach by utilizing three unmanned vehicles with a suite of sensors for persistent marine monitoring. Integration of a low power scientific echosounder in two of the autonomous surface vehicles are discussed in this paper; a Wave Glider (Liquid Robotics, Maritime Robotics) and a Sailbuoy (Offshore Sensing). Both vehicles are compact, cost-efficient platforms for persistent marine monitoring. We discuss key features of the systems and challenges in ensuring the collection of high-quality echosounder data. Experiences with the systems and examples of zooplankton echosounder data, collected over a period of six months on the highly productive Norwegian shelf outside Lofoten-Vesteralen, are presented and discussed.