A case study of habitat compensation to ameliorate impacts of hydroelectric development: effectiveness of re‐watering and habitat enhancement of an intermittent flood overflow channel

Abstract

Development of the Rose Blanche River, insular Newfoundland, Canada, for hydroelectricity resulted in destruction of fluvial habitat and habitat compensation was required to achieve ‘no net loss’(NNL) of habitat productive capacity. The preferred compensation alternative involved modification of a 1·2 km long natural high flow, flood bypass channel, wetted only during peak snow melt events. The channel consisted of 99·6 units (100 m2) of habitat and was modified, with hydraulic control structures, to ensure a constant regulated flow. Physical enhancement included addition of spawning gravels, bank stabilization, protection dykes to prevent flooding and installation of low head barriers to create pools. A 3 year study (2000–2002) was undertaken to assess: (1) habitat stability in the channel, (2) re‐population of the compensatory channel, (3) biological characteristics of fishes utilizing the channel and (4) movement and migration between the compensatory channel and the main river. Study results indicated evolution of meso‐habitat characteristics due to geomorphological and hydrological factors, with distribution of spawning gravels and increased input of organic matter. The channel was utilized preferentially by brook trout Salvelinus fontinalis, with a mix of size and age classes, indicating habitat use by all life stages. Total fish biomass over 3 years increased in the compensation channel while it decreased in the river main stem. Young‐of‐the‐year density was strong for both brook trout and Atlantic salmon Salmo salar in 2001 and 2002 suggesting good spawning and incubation conditions. Year class strength was less in the main river indicating differential (improved) survival in the compensatory habitat. Tag returns provided little evidence of site fidelity for both species suggesting considerable movement within the channel and possibly between the main river and channel. Habitat compensation effectiveness, in terms of NNL, determined that fish production in the compensatory channel achieved 69, 92 and 128% of lost production in 2000, 2001 and 2002, respectively. Fish production increased each year after development and NNL was achieved by the third year. The NNL was achieved in the compensatory channel which contained 100 units as opposed to the 570 units destroyed, a 1 : 5·7 ratio. The results of the study indicated that both habitat area and a measure of habitat productive capacity need to be considered in planning and assessing habitat compensation projects.