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Long-term continuous observations of zooplankton and fish from a cabledocean networkDavid Lemon, Gary Borstad, Leslie Brown, Paul Johnston, Jan Buermans & Eduardo LoosASL Environmental Sciences Inc., Victoria, BC, V8M 1Z5, Canadadlemon@aslenv.comAbstractLong time-series of continuous data from moored acoustic instruments offer a low-cost method to study ecosystemchanges by monitoring the behaviour and abundance of fish and zooplankton in the ocean and lakes. Calibratedmulti-frequency SONARs allow information about species composition and abundance to be deduced from acousticbackscatter. This paper will to describe the spatial behaviour of marine organisms. Long time-series of acoustic datain Saanich Inlet and the Strait of Georgia (British Columbia, Canada) have helped researchers understand the dielvertical migration of zooplankton as well as sockeye and pink salmon behaviour near the mouth of the Fraser River.IntroductionMoored, internally-recording acoustic instruments can acquire continuous profiles of echoes throughout the watercolumn, thus providing a low-cost method to study the behavior and abundance of fish and zooplankton in oceansand lakes (Trevorrow and Tanaka, 1997). Calibrated SONARs allow some information about species compositionand abundance to be deduced from acoustic backscatter (Holliday and Peiper, 1980). This paper will describe thecharacteristics of the single-frequency Acoustic Water Column Profiler (AWCP) and the more recent multifrequencyAcoustic Zooplankton and Fish Profiler (AZFP) instruments as well as results of their operation in coastalwaters.Single-frequency acoustic time-series in Saanich Inlet, BC, CanadaSeveral single-frequency AWCP instruments have been used for many years to continuously collect upward looking,single frequency data at high temporal and spatial resolutions at the cabled coastal ocean observatory of theVictoria Experimental Network Under the Sea (VENUS). In its autonomous configuration, the low power consumptionof the AWCP makes it possible to collect long time-series at high temporal and spatial resolutions, thus allowinginvestigation of seasonal and inter-annual variability acoustic data. Handling the large volume of data in suchlong time-series is challenging. To overcome this, the data cube concept (Figure 1) was employed to represent themeasured acoustic backscatter strength-depth/hour/day time-series (Borstad et al., 2011). The data cube shows a 14-month segment of backscatter at 200 kHz. The front of the cube illustrates the variation of backscatter as a functionof depth throughout the day, averaged at 10-minute intervals. Subsequent days are conceptually arranged in sequence.The top of the cube shows diurnal variations of backscatter near the surface over the 14-month deployment,dramatically illustrating long-term variations associated with changing day length. The front side of the cube showsthe seasonal changes in vertical distribution of backscatter at 1600 PST. Similar ‘slices’ can be made through thecube at any depth or hour of the day, thus greatly reducing the data volume and allowing analysis in readilyavailablesoftware packages.206