Effects of stocked trout on native fish and littoral invertebrates in boreal foothills lakes

In Alberta, fisheries managers stock non-native trout species into lakes to enhance angling opportunities. I assessed ecological effects of this management practice by comparing forage fish density, size structure, and habitat use, and littoral invertebrate community composition, abundance, and size structure, in five stocked and six unstocked lakes in the boreal foothills over three summers (2005-2007). Although altered size structure and changes in habitat use of forage fish were evident in stocked lakes, trout did not decrease forage fish densities in stocked relative to unstocked lakes. Similarly, few invertebrate taxa differed in abundance or size structure, and community composition did not differ between treatments. These productive lakes had abundant refuges for forage fish and invertebrates, and while trout preyed primarily on invertebrates, trout impacts were not detectable over the background forage fish impact. Thus, impacts of introduced trout on forage fish and littoral invertebrates in boreal foothills lakes appeared limited.