Sensitivity of fish density estimates to standard analytical procedures applied to Great Lakes hydroacoustic data |
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Authors: | Patrick M. Kocovsky Lars G. Rudstam Daniel L. Yule David M. Warner Ted Schaner Bernie Pientka John W. Deller Holly A. Waterfield Larry D. Witzel Patrick J. Sullivan |
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Affiliation: | 1. US Geological Survey, Lake Erie Biological Station, 6100 Columbus Avenue, Sandusky, OH 44870, USA;2. Cornell Biological Field Station, 900 Shackelton Point Road, Bridgeport, NY 13030, USA;3. US Geological Survey, Lake Superior Biological Station, 2800 Lake Shore Drive East, Ashland, WI 54806-2427, USA;4. US Geological Survey, Great Lakes Science Center, 1451 Green Road, Ann Arbor, MI 48105-2807, USA;5. Ontario Ministry of Natural Resources, Lake Ontario Management Unit, 41 Hatchery Lane, RR #4, Picton, Ontario K0K 2T0, Canada;6. Vermont Department of Fish and Wildlife, 111 West Street, Essex Junction, VT 05452, USA;g Ohio Department of Natural Resources, 1190 High Street, Fairport Harbor, OH 44077, USA;h SUNY Oneonta Biological Field Station, 5838 State Hwy 80, Cooperstown, NY 13326, USA;i Ontario Ministry of Natural Resources, 1 Passmore Street, Port Dover, Ontario N0A 1N0, Canada;j Cornell University, Department of Natural Resources, 214 Fernow Hall, Ithaca, NY 14850, USA |
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Abstract: | Standardized methods of data collection and analysis ensure quality and facilitate comparisons among systems. We evaluated the importance of three recommendations from the Standard Operating Procedure for hydroacoustics in the Laurentian Great Lakes (GLSOP) on density estimates of target species: noise subtraction; setting volume backscattering strength (Sv) thresholds from user-defined minimum target strength (TS) of interest (TS-based Sv threshold); and calculations of an index for multiple targets (Nv index) to identify and remove biased TS values. Eliminating noise had the predictable effect of decreasing density estimates in most lakes. Using the TS-based Sv threshold decreased fish densities in the middle and lower layers in the deepest lakes with abundant invertebrates (e.g., Mysis diluviana). Correcting for biased in situ TS increased measured density up to 86% in the shallower lakes, which had the highest fish densities. The current recommendations by the GLSOP significantly influence acoustic density estimates, but the degree of importance is lake dependent. Applying GLSOP recommendations, whether in the Laurentian Great Lakes or elsewhere, will improve our ability to compare results among lakes. We recommend further development of standards, including minimum TS and analytical cell size, for reducing the effect of biased in situ TS on density estimates. |
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Keywords: | Hydroacoustics Standard Operating Procedures Superior Michigan Huron Erie Ontario Champlain Otsego |
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