Seasonal variation in diet and trophic relationships within the fish communities of the lower Slave River, Northwest Territories, Canada

Increased industrial activities on the Peace and Athabasca River systems ha ve raised concerns about cumulative impacts on fish and water resources dow nstream, in the Slave River of Alberta and the Northwest Territories, Canad a. Because very little information was available on the fish communities in this system, we examined spatial and temporal patterns of diet for nine sp ecies (four piscivores and five invertebrate feeders) from three different types of habitat along the lower Slave River system and assessed trophic re lationships within the communities. All actively feeding species exhibited seasonal variations in diet within and among the study areas. Dietary overl ap was generally low throughout all seasons and locations. In the lower Sla ve River and is major tributary, the Salt River, substantial dietary overla p between piscivores (particularly walleye, Stizostedion vitreum), and inve rtebrate feeders occurred in the spring. In the summer no overlap occurred as walleye shifted to a more piscivorous diet, attaining a moderate degree of overlap with northern pike, Esox lucius. Compared with the Slave River, which is a large but homogeneous system upstream of its delta at Great Slav e Lake, there was a greater diversity of actively feeding invertebrate feed ers in the Salt River. Three of the latter were benthic feeders exhibiting moderate degrees of diet overlap during spring and summer. During the fall, few fish were feeding. Most fishes in the lower Slave River system are gen eralist, opportunistic feeders, consuming a number of different prey, the i mportance of which varies spatially and seasonally as the abundance of thes e prey varies in the environment.