Distribution patterns and feeding characteristics of rainbow smelt in Wisconsin : Effects on native fishes
The distribution of the exotic rainbow smelt (Osmerus mordax) is increasing in inland waters of the upper Great Lakes region of North America. The initial spread of smelt from Atlantic coastal areas of North America is the result of anthropogenic introductions and smelt currently inhabit many small inland lakes and reseviors in the upper Great Lakes, and Western Plains regions. In the upper Great Lakes region smelt are spreading through natural dispersal as well as additional introductions. Their spread in Vilas County, Wisconsin is augmented by the large number of lakes connected by streams and canals and smelt have recently colonized a number of lakes in this area. Predation by smelt negatively affects native fishes and there are many examples in published literature. Competition by smelt may also be a negative influence on native fish species, but examples documenting the effects are rare. The appearance of smelt in lakes studied by the Long Term Ecological Research (LTER) project provided a natural experiment and an established database suitable to examine the importance of competitive interactions between smelt and a native species, the yellow perch (Percajlavescens). In Crystal Lake, overlap in thermal habitat use by smelt and yellow perch ranged from 5 to 70\% from 1986-1993, and averaged 60\% during the thermally stratified period 1994. The use of prey resources by both species in 1994 was also very similar. Overlap in resource use by smelt and yellow perch along with the increase in smelt abundance, led to a significant decrease in the relative condition of perch showing the negative impacts of competition. Smelt are highly selective predators capable of feeding at low light levels. The feeding characteristics and distribution patterns of smelt indicate the potential for this species to have negative impacts on native species through competition and predation when introduced into new environments.