Ecosystem responses to sportfish stocking and aeration in boreal foothills lakes

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Throughout western North America, the stocking of inland waters that naturally lack sportfishes with non-native trout is a well-established management activity that creates new recreational fisheries. Alberta Sustainable Resource Development (ASRD) and the Alberta Conservation Association (ACA) currently stock lakes throughout the province, including small Boreal Foothills lakes. However, adding a top-predator into a fresh water ecosystem can have significant ecological impacts on potential trout competitors, and for aquatic invertebrates and amphibians that are the prey of the trout. These direct impacts can, in turn, affect other components of the food web. Unlike settings of most previous studies, however, the Boreal Foothills lakes of our study are more productive, and contain native populations of invertebrates and hardy forage fishes. Thelakes are often small and shallow and are therefore prone to winterkill for large, fast-growing fish such as trout.  In their fisheries management plan, the ACA has therefore implemented an aeration program for some of the stocked lakes. In its first phase (2005-2007) our project applied a "Control vs. Impact" study design, comparing nearby stocked and aerated, stocked and not aerated, and unstocked lakes. As ASRD stocks lakes we are studying that were previously unstocked, we can implement a "Before-After-Control-Impact" (BACI) design that is recognized as very powerful for studying ecological impact. We will monitor community consequences of stocking and aeration in this context by continuing to assess forage-fish population sizes, performing invertebrate and amphibian population surveys, as well as studying water quality and the food-web of the lake types through stable-isotope analysis. The research is important for managing sustainable recreational fishery in ways that minimizes its impact on native biodiversity. Our study provides us a unique opportunity to monitorthis stocking management program and develop strategies for the benefit of the ecological communities here (and elsewhere fish-stocking is implemented) and for the recreational interests of the region's residents and visitors.