Ecological Segregation Between Longnose and Blacknose Dace (Genus Rhinichthys) in the Mink River, Manitoba

Abstract

Longnose and blacknose dace occur in greatest abundance in the middle zone of the Mink River, and segregation in environment occupied is marked. Newly emerged longnose fry were found in stream margins, but by the middle of their first summer had moved into fast riffles (>45 cm/sec) where they completed their life cycle. Blacknose fry also occupied stream margins, remaining there for up to one year. Thereafter they were found mostly in channels of moderate current. Coexistence of fry of the two species in stream margins is minimized by earlier hatching of longnose dace. Diet of longnose and blacknose dace, consisting of aquatic insect larvae and nymphs, was strikingly similar.