Spawning Characteristics of Yellow Perch during Periods of Water Level Fluctuations in a Hydropower Reservoir

Abstract

Water level fluctuations alter reservoir ecosystems causing direct and indirect effects on fish populations. The dewatering of eggs, a direct impact of lake level drawdowns, can affect reproductive success of species that spawn in littoral zones, such as Yellow Perch. I examined relationships between water level fluctuations and spawning characteristics of Yellow Perch in a Central Appalachian hydropower reservoir, where water levels were permitted to be drawn down to 4 m and 2.1 m below the full pool elevation in March and April, respectively. Daily presences of egg masses were recorded on artificial spawning structures at two sites for the spring spawning seasons of 2019 and 2020. Spawning structures were placed at different distances from the shoreline, spanning water depths with and without the potential for dewatering based on the lowest permitted levels for lake elevation drawdowns. Generalized Estimation Equations (GEE) were used to analyze egg mass presence and six covariates: Secchi disk depth, distance to the shore, water temperature, water depth, lunar illumination, and lake level fluctuation. I also examined the proportion of egg masses in potential dewatering zones based on the minimum lake elevation drawdowns permitted for March and April. Data supported an additive effects model of Year + Water depth + Lunar illumination + Water temperature. The predicted probability of egg mass presence was negatively associated with water depth and lunar illumination, and positively associated with water temperature. A year effect, in part, reflected a between-year difference in the timing of spawning, where the number of egg masses during April exceeded that of March in 2019, a relationship that was reversed in 2020. During the 27-day spawning period in 2019, 52% (54 of 104) of egg masses had the potential to be dewatered, whereas 70% (30 of 43) had the potential to be dewatered in the 22-day spawning period of 2020. Our results have direct implications for fishery and hydropower management, as data on the characteristics and timing of spawning of yellow perch relative to water level fluctuations inform decisions regarding management of fish populations and lake level drawdown regulations.