Influence of water temperature and streambed stability on the abundance and distribution of slimy sculpin (Cottus cognatus)

Abstract

Sculpin are small-bodied fish that exhibit limited mobility. These fish may therefore be an ideal choice as sentinel species in environmental effects monitoring as they may be more reflective of ambient local conditions than are the large-bodied, more wide-ranging species historically used in monitoring programs. This study quantified the spatial and temporal density and distributional patterns of the slimy sculpin (Cottus cognatus) population in Catamaran Brook, New Brunswick, with the aim of gaining a better understanding of their response to natural environmental variability. We predicted that sculpin densities would follow a longitudinal temperature gradient from headwater to mouth and would be highly sensitive to fluctuations in stream flow and substrate disturbance. Electrofishing surveys conducted twice per year from 1991 to 1998 revealed significant differences in sculpin density between years, reaches, and habitats, but not between seasons. The highest sculpin densities were found in those reaches with the coolest summer water temperature. The Middle reach in Catamaran Brook annually supported the highest sculpin density, followed by the headwater or Upper reach and then by the two lowermost reaches: Gorge and Lower. Stochastic events also influenced population dynamics. A mid-winter ice break-up (1996) and its associated flood and ice scour caused the greatest disturbance of the sculpin population, resulting in a significant density decline and a shift in the population age structure. A bedload movement experiment conducted to further assess sculpins' response to substrate stability identified greater bed stability in the Upper and Middle reaches of the brook than in the Lower reach. The pattern of sculpin distribution observed in this study is consistent with the idea that distribution and abundance of sculpin are significantly influenced by stream temperature but also, in part, by stream bed stability.