Siscowet lake charr (Salvelinus namaycush siscowet) visual foraging habitat in relation to daily and seasonal light cycles

Using siscowet lake charr (Salvelinus namaycush siscowet) as an example organism, we modeled visual foraging habitat in relation to: (i) daily solar and lunar intensity, (ii) seasonal changes in maximum solar and lunar altitude, (iii) foraging for pelagic or benthic prey, and (iv) increased turbidity that may occur with climate change. Siscowet foraging success increased with light intensity and was higher for pelagic prey than benthic prey. Daily and seasonal siscowet foraging patterns were similar for benthic and pelagic prey types. Predicted day-time foraging depths were deepest in summer and shallowest in winter (range 172–233 m for pelagic prey and 210–283 m for benthic prey), and night-time foraging depths were deepest in winter and shallowest in summer (range 25–32 m for pelagic prey and 63–81 m for benthic prey). Within the Lake Superior basin, extreme precipitation events and associated sediment plumes can cause localized declines in light attenuation. Increases in turbidity associated with these sediment plumes can reduce predicted foraging depths by 65% and 80%, when compared to normal lake attenuation values. The model can be applied to predict how solar and lunar patterns influence foraging patterns in any aquatic organism that displays light-mediated behavior.