A Method for Estimating Gillnet Selectivity of Walleye (Stizostedion vitreum vitreum) in Muitimesh Multifilament Gill Nets in Lake Erie, and Its Application

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Abstract
A new method is described for adjusting gillnet catches for gear selectivity. Twelve years (1978–89) of walleye (Stizostedion vitreum vitreum) catches (n = 10 761) were pooled to derive frequency distributions of the ratios of fish girth and mesh perimeter for 11 mesh sizes. A gamma function was fitted to each of the 11 frequency distributions so that a selectivity curve could be derived for experimental gill nets used in Lake Erie, or any combination of meshes. An encounter model based on the swimming speed of walleye was used to estimate the probability of walleye encountering gill nets. Adjustments were made to walleye catches for both retention and encounter probabilities. Annual mortality and recruitment rates were compared for standardized and raw data from 1978 to 1989.

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