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USING A SIMULATED FISH COMMUNITY TO EVALUATE THE RELATIVE IMPORTANCE OF CATCHABILITY ON ABUNDANCE ESTIMATES FOR ACOUSTIC SURVEYS
2Great Lakes Science Center, 1451 Green Road, Ann Arbor, MI 48105.
3Great Lakes Science Center, Lake Superior Biological Station, 2800 Lakeshore Drive E., Ashland, WI 54806.
4Biology Department, University of Minnesota Duluth, 207 Swenson Science Building, 1035 Kirby Drive, Duluth, MN 55812.
5Michigan Department of Natural Resources, Charlevoix Fisheries Research Station, Charlevoix, MI 49720.
This projected consisted of three key components leading to the ability to evaluate the relative importance of two potential biases in fish density estimates derived from hydroacoustic/midwater trawl surveys (HMT). The first component was a workshop whose focus was to educate researchers on the issues that cause bias in HMT and to use expert knowledge of those researchers to develop methods for quantifying the degree of bias caused by variation in the availability of fish to HMT gears and trawl selectivity. The second component was the development of simulation software to support the estimation of the bias from these sources. The third was a manuscript that used the developed methods and software to quantify the degree of bias from these sources. A workshop was held in April 2014 and at this workshop we developed the methods and software, building on software funded by a previous GLFC grant. Subsequently, we developed, wrote, and submitted a manuscript to the journal Fisheries Research that described the research conducted. The degree of bias from varying availability and trawl selectivity varied depending on the fish community composition, fish size composition, and gear deployment methods. On average, trawl selectivity caused a larger bias in biomass density estimates than variation in availability to gear. However, in Lake Ontario the degree of bias was similar while in Lake Superior trawl selectivity induced bias was nearly four times that of limited availability to gear. Techniques for reducing the bias caused by trawl selectivity and limited availability were proposed.