Deregulation of the electric power market globally will lead to increased requirement for electricity on demand resulting in more emphasis on 'hydropeaking' generation. A research study was conducted on the regulated West Salmon River, Newfoundland, Canada, to examine habitat selection and movement of juvenile Atlantic salmon (Salmo salar) and brook trout (Salvelinus fontinalis) in response to flow changes related to 'experimental' peaking flow power generation. Fish were surgically implanted with microscale radio transmitters, released into an experimental study, and discharge was experimentally manipulated simulating two scenarios: (i) water storage during the day and generation at night, with a 2 hour transition; and (ii) night-time storage with generation during the day. Experiments were repeated in the summer and fall. Fish were tracked throughout the diurnal cycle of each manipulation and precisely positioned in two-dimensional space. Atlantic salmon exhibited two distinct patterns to movement: fish that showed high site fidelity and those that moved considerably during trials. Both salmon and trout were more active during fall hydropeaking experiments. Fish generally did not move long distances and moved more in a longitudinal fashion than laterally. Salmon moved greater distances, on average, than trout under all experimental conditions and during both seasons but these differences were not statistically significant. Brook trout moved more in relation to dynamic events (up-and down-ramping) than at steady state flows. Trout also moved more at night during these dynamic changes and under low flow conditions. These results will assist producers of hydroelectricity to reduce the impacts of hydropeaking operations on fish and fish habitat.

Variable 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 m 3 /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.

In insular Newfoundland, Canada, studies were conducted from 1999 to 2003 on the effects of 'simulated' hydropeaking power generation on juvenile Atlantic salmon (Salmo salar). In 1999, Atlantic salmon parr were released into an experimental reach below a hydroelectric facility and flow was manipulated over a range of discharge (1.0-4.2 m 3 s -1 ) during a series of 'experiments' simulating hydropeaking in both summer and fall. Fish were implanted with radio transmitters, manually tracked, precisely located (±1 m), habitat selection evaluated, and movement response determined. Experiments were continued in 2002 and 2003 to contrast response of salmon between summer and winter, the magnitude of flow changes were greater (0.7-5.2 m 3 s -1 ) and changes were made more rapidly (instantly). As discharge was increased, velocity and depth use by parr increased, and fish adapted behaviourally by increased contact with the substrate. Salmon parr also exhibited two distinct movement patterns in the summer and fall of 1999 studies; high site fidelity or considerable movement during trials. Salmon were more mobile during both static and dynamic flow conditions and throughout the diel cycle in the summer of 2002 experiment, and 2 fish were stranded and died, the only time this happened in the four series of experiments. Within each experiment generally there were no differences between movements at static high and low flows for day and night movements, with one exception, and night time movements were always greatest, again with one exception. During dynamic flow changes, within each experiment, distances moved during down ramping and up ramping were not significantly different except in the summer of 1999. Overall, comparing between experiments for up and down ramping events, distances moved in the summer of 2002 were statistically higher than for all other experiments. Not surprisingly, the home ranges of fish in the summer of 2002 were also the greatest while the smallest home ranges were in the winter of 2003. Results suggest hydropeaking regimes may be energetically costly potentially affecting over-winter survival which is related to energy reserves obtained during summer. Collectively these studies provide comprehensive information on the response of juvenile Atlantic salmon parr to hydropeaking, on both diel and seasonal scales, and will assist hydro producers and regulators design and operate hydropeaking regimes to minimize ecological impact.

Atlantic salmon Salmo salar smolts (n = 181) from two rivers were surgically implanted with acoustic transmitters and released to determine migration route, residency time and survival in a 50 km long estuarine fjord located on the south coast of Newfoundland, Canada. Data obtained from automated receivers placed throughout the Bay d'Espoir fjord indicated that migrating smolts used different routes to reach the outer areas of the fjord. The duration of time that smolts spent in the immediate estuary zone also differed between the two localities (7 and 17 days) although the total time smolts were resident in the fjord was similar and extensive (40 days). Many smolts were resident for periods of 4-8 weeks moving back and forth in the outer part of the fjord where maximum water depths range from 300 to 700 m. Survival in the estuary zone was greater for smolts with prolonged residency in estuarine habitat. Overall smolt survival to the fjord exit was moderately high (54-85%), indicating that the initial phase of migration did not coincide with a period of unusually high mortality.

A location-finding acoustic telemetry system (resolution ±1 m) was used to map ocean substrates and to continuously monitor the habitat associations (substrate, water temperature, and depth) of 58 Age 2 to 3 juvenile Atlantic cod Gadus morhua from 11 August to 20 December 1999. Substrate use was studied in 2 stages to determine if it differed from the pattern expected given an absence of selectivity (substrate use proportional to substrate availability). The first level compared the proportions of substrate in the study-area home ranges of Atlantic cod to those of the entire study site. The second assessed if the time spent over specific substrates was proportional to the substrate availability within the study-area home ranges. Boulder substrate was incorporated into the home ranges of juvenile Atlantic cod more than would be expected given its availability within the study area. Kelp substrates were included in these home ranges less than expected while sand and gravel were used in proportion to availability. Time spent over substrates within study-area home ranges varied over the diel and seasonal periods. Within study-area home ranges, juvenile cod occurred in boulder substrates at levels greater than or equal to availability. Conversely, the proportion of time spent over open substrates (e.g. sand and gravel) was either less than or not different from those of substrate availability. Kelp substrates were used less than expected in August and December and more than expected in September and October. Over the diel period, it was found that nocturnally, associations with structure diminished except during September and December when boulder habitats were still used to a greater degree. Unlike younger conspecifics, Age 2 to 3 cod in Buckley Cove were not strictly associated with structurally complex substrates, which suggests that these fish experience less vunerability to predation. Also, unlike younger conspecifics, the distribution of Age 2 to 3 cod did not shift inshore nocturnally and therefore they did not benefit metabolically by moving through the thermocline that existed from August to mid-November. This study indicates that substrate use by juvenile cod is dynamic and the strength of associations with structural complexity varies over diel and seasonal temporal scales.