Trawl and gill net selectivity of yellow perch in southern Lake Michigan, 1993-2006

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Thomas, Nathan D.
Lauer, Thomas E.
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Thesis (M.S.)
Department of Biology
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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.