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AbstractVariable hydropower production leads to hydropeaking, which causes discharge fluctuations that are potentially harmful to aquatic organisms. In this study, an experimental approach was used to investigate hydropeaking effects and associated hydraulic and habitat conditions on the home range and movement of juvenile Atlantic salmon Salmo salar. Prior studies examined the responses of Atlantic salmon and brook trout Salvelinus fontinalis to experimental hydropeaking during summer and autumn. The present study focused on Atlantic salmon, involved more rapid and extreme discharge manipulation, and included winter experiments to reflect influences of reduced temperature, ice conditions, and seasonal differences in behavior and habitat selection. Experiments were conducted over a range in discharge (0.5–5.0 m3/s) that resulted in dramatic habitat changes in the wide, shallow, boulder-strewn study reach. Experiments were repeated in summer and winter; however, the winter range in discharge was narrower due to constraints on water release. Fish response was monitored using manual telemetry in both seasons, and fixed telemetry was used to monitor fine-scale diel winter movements. Atlantic salmon had larger home ranges and were more mobile during all flow conditions and over diel cycles in summer than in winter, and there was anecdotal evidence of stranding in isolated pools in summer. Stream morphology, in addition to the magnitude of discharge change, was an important determinant of the propensity to move. In our study, there were considerable refugia from increased velocity and dewatering, which may have reduced the need to move. In winter, fish remained relatively sedentary in comparison with the summer foraging period, and this behavior may increase the likelihood for dewatering, stranding, and freezing. A secondary concern with hydropeaking regimes is the energetic cost to fish of moving to find suitable habitats, and during summer this cost could affect stored energy reserves, which could, in turn, affect overwinter survival.

AbstractProduction of brook trout Salvelinus fontinalisranged from 99 to 651 g · 100 m−2· year−1among headwater streams of the Copper Lake watershed in insular Newfoundland. Ratios of annual production to mean annual biomass (P/B) ranged from 0.9 to 1.5 among the same streams. Empirical models developed from stream salmonid populations in the United States successfully predicted modal production based on water alkalinity and P/Bratios based on age-class structure of the populations. Differences in production among streams were consistent with previous work in low-fertility headwater systems, which suggests habitat attributes of the stream define salmonid production within the range dictated by the water fertility. The most important of these attributes in this study was food abundance. Substrate composition and habitat complexity may have played secondary roles in determining production in the most productive stream.

AbstractFine-sediment infiltration was monitored by the Wesche sediment method in the Copper Lake watershed, Newfoundland, Canada, from June 1993 to October 1994 as part of a multidisciplinary forest harvesting buffer zone research project. Initial study in Copper Lake has focused on evaluating the ability of this method to measure sediment dynamics in small boreal forest streams and in developing methods for data analyses and interpretation. The Wesche method discerned expected differences in sediment yield among sites due to logging-road construction and seasonal trends. Stream reaches impacted by bridge construction and culvert installation had significantly higher sediment accumulation than streams not affected by road construction. The Wesche method was a relatively simple and inexpensive way to compare fine sediment yield in streams with similar hydrologic regimes and was easily used in remote locations. Due to the nonparametric nature of the data collected with this method, randomization techniques were used to develop 95% confidence intervals around the mean. Use of these statistics allowed a significance level to be used in comparisons between stream reaches, an approach easily understood by the multidisciplinary audience interested in fishery–forestry research and management.