Utilizing External Features and a Consensus Field-Based Approach to Determine Sex of Lake Michigan Yellow Perch

Understanding fluctuations in population sex ratios is important for evaluating the effects of changes in population demographics and for making informed management decisions. The Yellow Perch <i>Perca flavescens</i>, an important sport fish in Lake Michigan, undergoes sexually dimorphic growth, likely resulting in differing vulnerabilities to angler harvest. However, sex ratio data from angler-harvested fish have not been collected because of the handling time and intrusiveness of the methods for distinguishing sexes. We utilized digital photographs of the urogenital papilla (UGP) from known-sex Yellow Perch to establish a method whereby UGP shape could be used to rapidly, accurately, and inexpensively determine the sex of Yellow Perch. Overall, 88.1% of Yellow Perch examined were assigned to the correct sex, and the sex ratio estimate of 48:87 (female : male) did not differ significantly from the known sex ratio of 46:89. Classification success was not affected by fish sex, TL, or month of collection. Our results demonstrate accurate, rapid, inexpensive, and nonlethal applicability of this method across a wide range of sizes and geographic and temporal scales. Applying this methodology will permit accurate sex ratio estimates for angler-harvested Yellow Perch, which can be used to better understand harvest composition and its implications for management. Received February 17, 2017; accepted June 9, 2017 Published online August 31, 2017