Assessment of Two Denil Fishways for Passage of Freshwater Species
Fisheries Bioengineering Symposium: American Fisheries Society Symposium 10
Colt J;White RJ;
American Fisheries Society
Fish movements through two Denil fishways were assessed by means of traps at the fish exit (upstream end) of each facility. Located in the Canadian prairies, the Fairford (Manitoba) and Cowan (Saskatchewan) fishways are similar in design and operation. At Fairford, 8,871 fish representing 13 species were caught in the trap, which was operated daily May 6-28 and June 2-12, 1987. White suckers Catostomus commersoni, walleyes Stizostedion vitreum, and saugers Stizostedion canadense made up 93.0% of the run. The Cowan fishway was assessed daily from April 27 to May 11, 1985, and weekly thereafter until June 10, 1985. The four species caught were white suckers, longnose suckers Catostomus catostomus, northern pike Esox lucius, and walleyes; 11,294 fish were trapped, although it was estimated that over 23,000 fish passed through the fishway. The size range of fish that passed through the fishways was 212-800mm. The longest Denil fishway section negotiated was 9.5 m at a 12.6% slope. Headwater levels at Fairford were fairly constant, but they decreased at Cowan over the study period. Water depths at the upstream end of the fishways ranged from 0.5 to 1.0 at Fairford and from 1.2 to 0.8 at Cowan. Estimated water velocities were low near the bottom of each fishway (0.7-0.9 m/s) and high near the water surface (>1.5 m/s). Although fish movements at both sites were likely obstructed by dams for several decades, all species present ascended the fishways readily. Northern Pike, though appeared to wait 2 to 3 weeks before using the fishway at Cowan. Long residence time by northern pike below this and other dams may be a reflection of behavior in relation to foraging, spawning, or passing through Denil fishways.