Operational requirements for observing marine ecosystems with acoustics

Acoustics resolve components of the ecosystem in time and space better than other methods. Additional sensors are needed to support the acoustic information with respect to identifications of specific targets and for including the biological information in the context of their physical environment. Using acoustics in advanced platforms enable simultaneous and continuous collection of biological and physical date, a prerequisite for understanding physical drivers and biological responses. In ecology and ecosystem based fisheries management the need for basic knowledge about the fundamental processes from individual to population has become urgent. Understanding of ecosystems function and quantification of basic processes require true resolution in time and space. In this presentation I will consider the time-space issue related to observation of marine ecosystem. The limitations of vessel based sensors are discussed, and the potential compensation of these limitations with profiling and towed systems as well with stationary systems is demonstrated. The operation of a profiling system facilitates constant observation volume for all frequencies throughout the water column. A camera system may take pictures during the profiling that may help validating the acoustic recording. Similarly, a towed system, undulating over certain depth ranges, gives high resolution data over the searching depth that can be compared to vessel information. These solutions in particular take into account the spatial limitation of vessel systems and might become crucial supplements to standard survey procedures. However, vessel, profilers and towed systems to a varying degree mix time and space (moving sensors over time). Only stationary systems observe ecosystems components with true temporal resolution. Particular emphasis will be paid to observatory solutions by presenting a cabled observatory now being launched off Vesterålen, an oceanographic and ecological hotspot. It is planned - o extend the cable to the shelf break and thereby establish a line of sensors from shore to deep water. The potential of such an acoustic observatory is discussed based on data received from similar battery operated stationary systems.