Visual Sensitivity, Behavior, and Habitat of Select North American Fishe

This dissertation examines how both physiological and behavioral techniques can be used to address the visual capabilities of three low-light foraging species, the walleye (Sander vitreus), siscowet lake trout (Salvelinus namaycush siscowet), and deepwater sculpin ( Myoxocephalus thompsonii). Visual physiology studies can reveal the specific wavelengths fish have adapted to detect at low light intensities while behavioral studies determine the minimal light intensities needed to forage, which may ultimately reveal habitat characteristics important to individual species. Our first study used electroretinography to determine the scotopic spectral sensitivity of the walleye dark-adapted retina (peak sensitivity 500--550 nm) in addition to the approximate maximum depths where visually mediated behavior may occur during the day (77.5 m) and at night (11.3 m) for kPAR = 0.3. For our second study, we found that siscowet lake trout reaction distance to deepwater sculpin increased with increasing light intensity (up to 6.0 x 109 photons m--2 s--1, thereafter remaining constant), but was not affected by substrate type. Third, we determined that the average number of deepwater sculpin movements per trial increased with decreasing light intensity in the presence of siscowet lake trout, where both activity and reaction distance were suppressed at upper light intensities. Finally, we used solar/lunar patterns to predict how siscowet lake trout visual foraging habitat changes on a daily and seasonal basis. Our model predicted the deepest daytime foraging depths in summer (232.9 m), while the deepest nighttime foraging depths were predicted in winter (32.1 m). Collectively, the findings of these visual studies allow for the improvement of foraging models as well as defining foraging habitat that describes when and where fish may forage.