Influence of Environmental Factors and Piscivory in Structuring Fish Assemblages of Small Alberta Lakes

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Abstract
We surveyed 45 small lakes in central Alberta to determine if discrete, repeatable types of fish assemblages exist, to identify the main environmental and biotic processes likely responsible for assemblage-level patterns, and to compare and contrast Alberta patterns with those observed in other regions of North America. Overall, 11 species of fish were caught in 36 lakes; nine lakes were fishless. Hierarchical classification and detrended correspondence analysis of fish species presence/absence identified two main assemblage types, characterized by northern pike (Esox lucius) and yellow perch (Perca flavescens) versus brook stickleback (Culaea inconstans) and fathead minnow (Pimephales promelas). Pike/perchlakes were significantly deeper and larger than lakes of the stickleback/fathead assemblage type; however, a subset of the former group lacking yellow perch was environmentally similar to stickleback/fathead lakes. Piscivory by northern pike appears to be the dominant process maintaining nearly complete negative assocaitions between members of the two assemblage types. Despite environmental and faunal-richness differences, our results were not unlike those from southern Ontario and northern Wisconsin [USA]. For small boreal lakes of North America, piscivory and processes related to a small number of environmental variables, such as maximum depth, surface area, and isolation, appear to be most important in structuring fish assemblages.