Selectivity of trawl and experimental gill nets was determined for yellow perch taken from southern Lake Michigan in 1993 to 2006. Gill nets were comprised of 51-, 64-and 76-mm size mesh and showed female modal lengths of 205-, 245-, and 295-mm, respectively, while values for males were 200-, 230-, and 267-mm. Differences between females and males increased with mesh size and was significant. Comparison of nine anterior morphometric features of female and male fish indicated no differences in shape were identified that would cause the disparity in selectivity. Rather, differences in male and female selectivity were more likely due the variant population size structure of the local population sampled, with females the larger sex. A new method to estimate trawl selectivity was developed using a modified catch-curve analysis, which showed a maximum selectivity length value (1.0) of 190-mm for females and 170-mm for males. However, trawls fail to capture larger yellow perch when compared to gill nets using based on length-frequency distributions. Revealing such gear biases may lead to more efficient capture methods, resulting in improved sampling and quantitative assessment of fish populations. / Department of Biology

I determined differences in yellow perch gill-net catch-per-unit-effort (CPUE) at two depths (10 and 15 m) in the Indiana waters of Lake Michigan during June, July, and August from 1989 to 2006. I evaluated the abiotic factors of water temperature, water clarity, wave height, and wind direction to determine whether they influence the differences in yellow perch CPUE. This study suggests that yellow perch in southern Lake Michigan may select habitat based on water temperature during the summer, moving in response to thermocline changes. We also evaluated mortality rates for two distinct periods (1984-1994 and 2000-2007) in order to identify the response of the population to changes in exploitation. Yellow perch during 1984-1994 (high exploitation) and 2000-2007 (low exploitation) displayed an increase in mortality for fish of harvestable size. In addition, during 2000-2007 (low exploitation) we identified that female yellow perch reached exploitable size earlier in life than males. / Department of Biology

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