Midwest Fish & Wildlife Conference 2018

AUTHORS. Trevor D. Keyler, Thomas R. Hrabik, Loranzie Rogers - University of Minnesota Duluth; Owen Gorman, US Geological Survey

ABSTRACT. The foraging characteristics of siscowet lake trout (Salvelinus namaycush siscowet) on deepwater sculpin (Myoxocephalus thompsonii) and the predator response of the sculpin were determined during laboratory trials under ecologically relevant light intensities ranging from 9.0×108 to 1.62 ×1011 photons m-2 s-1 and on varying substrates including pea gravel, sand, and black fabric. Siscowet reaction distance in response to the benthic 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. When compared to pelagic prey data, average reaction distances were lower at each light intensity for benthic prey. Prey capture increased with increasing light intensity and a strong correlation was found between the overall probability of prey capture and siscowet reaction distance at corresponding light intensities. Siscowet reaction distance to deepwater sculpin was not significantly different between 60° increments along the siscowet midline (forward, lateral or rear visual sectors) and siscowet remained active at all non-zero light levels. Finally, a predictive model for reaction distance to benthic prey was successfully developed to determine reaction distances for siscowet in various photic environments. Comparatively, deepwater sculpin reaction distance was affected by both light intensity andforaging arena substrate. Sculpin reaction distance to siscowet showed a parabolic trend with increasing light intensity characterized by suppressed reaction distances in the dark, peaking at mid-range light intensities (between 3.05×109 and 6.0×109 photons m-2 s-1) and declining again at the upper tested light intensities. The average number of sculpin movements per trial increased with decreasing light intensity (until 3.05×109 photons m-2 s-1 where after remaining constant) and the greatest increase in sculpin movement occurred from 6.0×109 to 3.05×109 photons m-2 s-1, the same intensity transition where siscowet reaction distance and prey capture both show a greater decline.