Fish Assemblage in Southern Alberta Reservoirs, 2003
Jason A. Cooper
In an effort to determine fish community structure, the Alberta Conservation Association (ACA) sampled nine irrigation reservoirs in southern Alberta between 26 May and 22 August 2003. The study included the following reservoirs: Crawling Valley, Fincastle, Forty Mile Coulee, Keho, Lake McGregor, Lake Newell, Little Bow, Milk River Ridge and Rattlesnake/Sauder.
Fourteen fish species comprising seven families were caught by beach seine (91%) and gill net (9%). Among sport fish, walleye, northern pike, and lake whitefish occurred in all reservoirs. Yellow perch was sampled in all reservoirs except Milk River Ridge and Keho reservoirs, where the species does not occur. Yellow perch was the most abundant sport fish, constituting 30% and 75% of the beach seine and gill net catches, respectively. Walleye comprised less than 1% and 5% of the beach seine and gill net catches, respectively. Although adult walleye were captured from all reservoirs, young‐of‐the‐year (yoy; n = 221) were captured in seven of the nine reservoirs only; the exceptions were Fincastle and Little Bow reservoirs. Crawling Valley Reservoir had the highest catch of yoy walleye (n = 127). Overall, spottail shiner, a non‐sport fish species, was the most abundant species captured (n = 46,318), and lake chub, longnose dace, and burbot were the least abundant species (n = 1 for each species).
Overall, gill net catch‐per‐unit‐effort (CPUE) for walleye ranged from 1.2 fish/91.4 m/24 h in Fincastle Reservoir to 50.2 fish/91.4 m/24 h in Crawling Valley Reservoir. CPUE for northern pike ranged from 1.7 fish/91.4 m/24 h in Milk River Ridge Reservoir to 14.4 fish/91.4 m/24 h in Forty Mile Coulee Reservoir. Yellow perch had the highest CPUE, ranging from 0.0 fish/91.4 m/24 h in Crawling Valley Reservoir to 829.3 fish/91.4 m /24 h in Fincastle Reservoir. CPUE for lake whitefish ranged from 134.5 fish/91.4 m/24 h in Milk River Ridge Reservoir to 2.9 fish/91.4 m/24 h in Fincastle Reservoir. No burbot were captured in gill nets in any of the reservoirs; however, this species is known to
exist in all reservoirs.
Overall, beach seine CPUE for walleye ranged from 0.0 fish/100 m2 in Little Bow and Fincastle reservoirs to 0.7 fish/100 m2 in Crawling Valley Reservoir. CPUE for northern pike ranged from 0.0 fish/100 m2 in Keho Lake to 0.2 fish/100 m2 in Crawling Valley Reservoir. Again, yellow perch had the highest CPUE, ranging from 0.5 fish/100 m2 in Crawling Valley Reservoir to 98.5 fish/100 m2 in Lake Newell. CPUE for lake whitefish ranged from 0.0 fish/100 m2 in Crawling Valley, Fincastle, Forty Mile Coulee and Rattlesnake/Sauder reservoirs to 35.4 fish/100 m2 in Lake Newell. Only one burbot was captured by beach seine in Rattlesnake/Sauder Reservoir even though this species is
known to exist in all reservoirs.
The dominant year‐class of walleye shifted from the stocked 1991 cohort to the naturally‐recruited 1998 cohort, especially in Keho Lake, Forty Mile Coulee, Lake McGregor, and Rattlesnake/Sauder reservoirs. Growth rate for walleye was highest in Keho Lake, and lowest in Milk River Ridge Reservoir. In general, average age‐at‐firstmaturity for walleye was 5 y for both males (range = 4 – 6 y) and females (range = 4 ‐ 7 y). The Rattlesnake/Sauder Reservoir population had the earliest age‐at‐first‐maturity for male walleye (4 y) and Forty Mile Coulee and Milk River Ridge reservoirs had the
most delayed age‐at‐first‐maturity (6 y) for males. Similarly, Lake Newell walleye had the earliest age‐at‐first‐maturity for female walleye (4 y), whereas Milk River Ridge Reservoir had the most delayed (7 y).
Overall, walleye recruitment between 1996 and 2003 in the nine surveyed reservoirs has been variable. Mean beach seine CPUEs for yoy walleye ranged from 0.0 fish/100 m2 in Fincastle and Little Bow reservoirs to 1.06 fish/100 m2 in Crawling Valley Reservoir. Crawling Valley Reservoir exhibited the highest natural walleye recruitment over the eight‐year period (1996 ‐ 2003). The data collected over the last eight years suggests that natural walleye recruitment is occurring in seven of the nine reservoirs surveyed in 2003; the exceptions are Fincastle and Little Bow reservoirs.