Seasonal and Ontogenic Shifts in Microhabitat Selection by Fishes in the Shallow Waters of the Detroit River, a Large Connecting Channel

Abstract

We examined the relationship between microhabitat variables and fish distributions in a large connecting channel, the Detroit River. Fishes were sampled by boat seine at 60 sites in shallow (<2.5 m) Canadian waters in May, July, and September 2004. Length-frequency distributions were used to separate species into small- and large-species size categories. Fish–microhabitat associations were examined by applying canonical correspondence analysis separately for each season. Small fishes were often more strongly associated with microhabitat variables than large conspecifics. For example, small centrarchids were more strongly associated with complex macrophytes than large centrarchids in the spring; however, this pattern varied among seasons. We attribute the stronger microhabitat associations of small fishes to predator avoidance. Small-bodied species also selected habitats that provided protection against predation: The spotfin shiner Cyprinella spiloptera preferred shallow water, and the round goby Neogobius melanostomus preferred coarse substrate. We observed a strong difference in microhabitat preferences between the small and large size categories of a species. Fish size played a greater role than season in determining fish–microhabitat associations. We found that macrophytes with a complex morphological structure were the most important factor in determining fish distributions in all seasons, while depth ranked second or third in importance. Fishes use an array of microhabitats in the Detroit River, and habitat heterogeneity is essential for promoting a diverse fish assemblage.