Evaluating the scotopic visual sensitivity of walleye (Sander vitreus) and implications for foraging habitat
Abstract
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 m and 1.9 m, respectively. These depth estimates exceed commonly reported habitat use, suggesting that vision may remain functional beyond expected depth ranges. Our findings support the visual pigment sensitivity hypothesis and provide a physiological basis for understanding the spatial and temporal foraging strategies of walleye across diverse freshwater environments.