Juvenile Walleye (Sander vitreus) Foraging Behavior, Success, and Growth Under Varying Light Conditions

Abstract

The foraging success and growth of piscivores often depend on environmental light availability. In north-temperate systems, high tannin concentrations limit light, and increasing variability in tannin levels may influence fish foraging behavior, success, growth, and further contribute to varying recruitment trends. To evaluate foraging and growth responses to varying light conditions, we studied juvenile Walleye (Sander vitreus) reaction distances and successful attacks/captures of prey at multiple light intensities (0, 0.05, 0.1, 1, 10, 40, 100, and 750 lux) and observed their growth at 3 of these light intensities (10, 100, and 750 lux) under various tannin concentrations (0 mg/L, 10 mg/L, and 20 mg/L). To study foraging behavior and
success, juvenile Walleye (109-156 mm) foraged for 15 minutes on three Fathead Minnows (Pimephales promelas) in a 1900L foraging arena. Reaction distance and successful attacks/captures were calculated from video recordings. To study growth, 15 juvenile Walleye (127-182 mm) were randomly assigned to a treatment at one of three light intensities and tannin concentrations and fed ad-libitum at 18°C for 16 days. Total length and weight were measured at days 0, 8, and 16 and consumption was measured each day for each replicate. Capture success was greatest in very low light conditions (0.05-1 lux) and declined as light intensity increased. Walleye reaction distance increased from 0-1 lux and plateaued, but the
probability of an attack decreased with increased light intensity. Juvenile Walleye growth was always positive and ranged from 0.010 to 0.023 g/g/day, with the greatest growth occurring in low light (10 lux) with highly stained water (20 mg/L). At each light level, tannin concentrations of 0mg/L had the lowest growth rates. These findings highlight the importance of low-light habitats for age-0 Walleye and provide insights into how changing light conditions and water clarity may affect foraging and growth in north-temperate systems.