Population Dynamics of Spawning Walleye in Otsego Lake, NY

Abstract

Walleye (Sander vitreus) are recreationally and ecologically important throughout New York State waterbodies. The species has been stocked throughout the state for purposes of establishing and enhancing recreational fisheries and biological control of landlocked alewife populations and milfoil management in the state. In populations supported by large-scale stocking efforts, we rarely collect information about natural reproduction. Walleye were stocked from 2000-2014 in Otsego Lake, New York for biological control of alewife (Alosa pseudoharengus) with a secondary purpose of re-establishing a recreational fishery. Following the functional elimination of alewife from the lake, walleye stocking ceased and their population has been supported only by natural reproduction. With the collapse of the alewife population and the increased popularity of a harvest-orientation for walleye, the status of the population and the ability to sustain a fishery into the future is currently uncertain. The purpose of this thesis was to characterize baseline population dynamics of spawning walleye in Otsego Lake, NY following successful re-introduction of the species and establishment of wild reproduction. To achieve this, the specific objectives of my thesis were to: 1) characterize spawning walleye demographics (age, growth, sex ratio, and size distribution), 2) estimate annual survival and population abundance of stream-spawning walleye in the lake, and 3) quantify variability in reproductive phenology as related to environmental cues to inform future sampling efforts. Sex ratios of spawning fish were heavily skewed toward males, but the proportion of females in spawning tributaries has increased in recent years. We found that mean size and age of spawning walleye varied between males and females but increased across sexes during the study period. Additionally, estimated population abundance decreased markedly from about 6,428 individuals in 2008 to 1,724 individuals in 2017 before stabilizing at about 868 individuals in 2018 and 748 individuals in 2019. Taken as a whole, these changes suggest that the naturally reproducing walleye population may be stabilizing at numbers lower than were sustained during years of active stocking, which may affect how harvest influences the population in the future. Finally, I was able to create predictive relationships between environmental variables of interest (date, photoperiod, and degree days) that were useful for predicting the initiation of spawning accurately and, with a precision of about one week, to facilitate more efficient sampling of this population in the future. The information provided by this study will facilitate future management of Otsego Lake. Continued monitoring of this population will help resolve or confirm some of the outstanding uncertainties related to current stock status and trends observed.