Gillnet bycatch and discard assessments of walleye, yellow perch and white perch from Lake Eire commercial fisheries

Theoretical gillnet bycatch of walleye (Sander vitreus), yellow perch (Perca flavescens) and white perch (Morone americana) in Lake Erie commercial fisheries during 1994 to 2007 was predicted using a delta model that was developed based on the fishery-independent survey data. The delta model consisted of one generalized additive model to predict positive bycatch, and one AdaBoost model to predict the probability of non-zero bycatch. Discards for each species were estimated as the difference between theoretical bycatch that was predicted from the delta model and retained bycatch that was recorded in the commercial data.  The probability distributions of bycatch and discards for each species were obtained using a bootstrap approach. As a result, the discards of walleye were higher when targeting yellow perch, fishing in Pennsylvania ridge, and fishing in August through October. More discards of yellow perch and white perch were obtained when fishing in west/west central basin. Targeting white perch and white bass resulted in higher discards of yellow perch. We suggested that gillnet bycatch and discards of these three species be considered in the future data synthesis as part of the stock assessment although the magnitude of discards were found not to be considerably large in this analysis.