Springtime migration by Mountain Whitefish: A journey for food?

Abstract

Mountain Whitefish (Prosopium williamsoni) are native to the entire state of Montana. The Smith River basin, in central Montana, encompasses numerous tributaries with little fragmentation. Recent studies have observed Mountain Whitefish traveling long distances through the watershed during peak spring runoff. The cause for these movements is not well understood. Thus the objectives of this study are 1) to describe the benthic macroinvertebrate community structure 2) to describe dietary requirements of Mountain Whitefish and 3) compare Mountain Whitefish diets and non-native Rainbow Trout diets (Oncorhynchus mykiss) in the Smith River and Sheep Creek. Benthic samples from both Smith River and Sheep Creek indicate large diversity in potential food items. Mountain Whitefish diets are diverse including numerous benthic macroinvertebrate families whereas Rainbow Trout diets are less diverse encompassing fewer families per diet. Ephemeroptera families have dominated diets of both species. Thus potential competition between the native Mountain Whitefish and non-native Rainbow Trout is plausible in areas of high fish abundance and limited common prey items.