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Tuesday, January 30 • 4:00pm - 4:20pm
SYMPOSIA-07: Hydroacoustic Estimates of Prey-fish Abundance Change with Various Analytical Decisions

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AUTHORS. Rebecca A. Dillon, The Ohio State University; Joseph D. Conroy, Ohio Department of Natural Resources, Division of Wildlife; Stuart A. Ludsin, The Ohio State University

ABSTRACT. To best inform management decisions (e.g., harvest quotas, and stocking levels), accurate and precise estimates of fish abundance are needed. Toward improving our ability to estimate fish abundance in shallow freshwater ecosystems, we determined how aspects of a hydroacoustics processing protocol developed for the North American Great Lakes (i.e., Great Lakes Standard Operating Procedure, GL-SOP) influenced estimates of prey-fish density and target strength in five Ohio reservoirs sampled during August 2016. Specifically, we quantified how prey-fish density estimates were influenced by consideration of three key aspects of the GL-SOP: 1) removal of background noise; 2) a lower maximum beam compensation (MBC) setting; and 3) application of the Sawada index (Nv) to identify and replace biased in situ cell-specific target strength (TS). These estimates were made using the existing Ohio Division of Wildlife SOP for processing hydroacoustics data, as well as procedures that included the three GL-SLOP recommendations in isolation and in combination. Our analyses showed that the removal of background noise had little effect (-1.3 to 0.0% change), while changing the MBC from 12 to 6 dB had a large potential effect (21.4 to 64.9% increase in density). The effect of using the Sawada index was intermediate, and highly inconsistent (-24.3 to 9.8%). W.hen all three GL-SOP recommendations were simultaneously applied, prey-fish density estimates increased by 12.9 to 23.6%. Our findings indicate the need for the Ohio Division of Wildlife to consider altering its current hydroacoustic processing SOP for reservoirs, as well as to reassess past estimates of prey-fish abundance. Our results suggest the need for agencies to periodically re-evaluate their SOPs, to ensure that their estimates of prey-fish abundance are as robust as possible. Doing so will maximize the ability of agencies to make informed management decisions.

Tuesday January 30, 2018 4:00pm - 4:20pm CST