Browsing by Subject "Light intensity"

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    Comparison Of Multi-Piscivore Foraging Success On Native And Invasive Prey Fish Under Variable Light Intensities
    (2020-05) Michels, Noland
    The majority of fish predator-prey studies have focused on interactions using a single predator. We explored the complexity of foraging at different times of the day by examining the interactions of paired native predators (Burbot Lota lota or Smallmouth Bass Micropterus dolomieu) with either native (Mottled Sculpin Cottus bairdii) or invasive (Round Goby Neogobius melanostomus) benthic prey (n=20). The study allowed the comparison of a pursuit (Smallmouth Bass) and ambush (Burbot) predator. Trials were performed under natural relevant lighting conditions with downwelling light intensity and emission spectrum matched to the irradiance at 10 m depth found in the St. Louis River estuary during summer at night, civil twilight, sunrise, and midmorning. Smallmouth Bass were more active than burbot and initiated 1,510 reactions that resulted in the successful capture of 61 Round Goby and 103 Mottled Sculpin (10.9% success rate overall) whereas Burbot initiated 475 reactions resulting in 24 successful retentions including 9 Round Goby and 15 Mottled Sculpin (5.0% success rate overall). The percentage of successful retentions was greater for Smallmouth Bass at 10.9% compared to only 5.0% for Burbot. Reaction probabilities to each prey differed significantly which resulted in a two-fold increase in attacks on Mottled Sculpin compared to Round Gobies within the same time period. Reaction distances for both predator species did not differ in regard to prey species, but Smallmouth Bass reacted farther than Burbot (max. reaction distances of 159 and 98 cm, respectively). Greater success of native predators on native prey likely cause predators to expend more energy capturing invasive prey and cause higher mortality on native prey populations due to greater predator success.
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    Visual Sensitivity, Behavior, and Habitat of Select North American Fishes
    (2018-05) Keyler, Trevor
    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 6.0×109 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.