Assessing Fish Habitat Compensation Projects on the Barrenlands Tundra, Northwest Territories

Fish and other aquatic organisms depend on quality habitat, but human activities can degrade aquatic habitats.  In Canada, the Fisheries Act mandates “no net loss” (NNL) of the productive capacity of fish habitat (i.e., its ability to produce healthy fish, or organisms upon which fish depend).  In compliance with NNL provisions, Diavik Diamond Mines, Inc. plans two compensation projects to increase habitat quality of small lake-outlet streams and improve connectivity among small lakes in the greater Lac de Gras (Northwest Territories) watershed.  As part of a before-after-control-impact design to assess these projects, we sampled four lake-stream systems designated for manipulation and three unmodified control systems for fish, invertebrates, primary producers, hydrology, and habitat characteristics over three years prior to habitat manipulation.  Netting and electrofishing surveys revealed that lake fish assemblages contain 3 - 7 species (mean ± SE; 4.29 ± 0.75), consisting mainly of lake trout (Salvelinus namaycush), Arctic grayling (Thymallus arcticus), round whitefish (Prosopium cylindraceum), burbot (Lota lota), and slimy sculpin (Cottus cognatus).  Because of low, diffuse flows and cascades that obstruct upstream movement of fish from Lac de Gras, streams support few species of fish (mean ± SE; 2.57 ± 0.57).  Stream communities are instead diverse assemblages of invertebrates, especially dipterans, crustaceans, Oligochaeta, Mollusca, and Hydrachnidia.  Stream and lake riparian zones are dominated by boulders, mosses, grasses, forbs, and shrubs. Water quality, as indicated by total nitrogen (TN), total phosphorous (TP), and chlorophyll-a (Chl-a), is similar among streams (mean ± SE; TN = 246.91 ± 3.53 µg/L; TP = 8.25 ± 0.60 µg/L; Chl-a = 1.42 ± 0.27 µg/L), while all seven lakes are oligotrophic (mean ± SE; TN = 250.08 ± 4.88 µg/L; TP = 6.58 ± 0.36 µg/L; Chl-a = 1.50 ± 0.17 µg/L).  After the habitat manipulations are completed in the autumn of 2011, community structure and system productivity will continue to be studied for two years to assess effects on physical, chemical, and biological characteristics of these small, Arctic lakes and streams.  We are also characterizing food web structure in a subset of lakes using stable isotope analysis to determine the influence of fish community composition on lake trout trophic ecology.  Results from this study should increase our ability to predict and understand new food-web organization that occurs as a result of the habitat manipulation.