Evaluating the scotopic visual sensitivity of walleye (Sander vitreus) and implications for foraging habitat

Understanding the physiological limits of visual detection is essential for delineating habitat use in freshwater fishes. Walleye (Sander vitreus), a crepuscular predator with well-documented low-light foraging capabilities, exhibits visual adaptations suited for dim environments. Using electroretinography (ERG), we determined the scotopic spectral sensitivity of adult S. vitreus and modeled their potential visual foraging depth under a range of optical conditions. Peak spectral sensitivity occurred between 500-550 nm, aligning with wavelengths that penetrate mesotrophic systems most effectively. We used ERG-derived irradiance thresholds in combination with the Beer-Lambert light attenuation model to estimate maximum depths for visual detection under solar and lunar illumination across a range of turbidity levels. Results indicate that under daylight conditions, S. vitreus can detect light to depths exceeding 77 m in clear water (kPAR = 0.3) and ~13 m in turbid systems (kPAR = 1.2). Under moonlight, detection is possible to 11.3 and 1.9 m, respectively. These depth estimates exceed commonly reported habitat use, suggesting that vision may remain functional beyond expected depth ranges. These results provide a physiological basis for understanding the depth limits and illumination conditions under which scotopic vision may remain functional in walleye across freshwater systems of varying water clarity (kPAR).