Status of the Walleye Fishery at Crawling Valley Reservoir, Alberta, 2004
Jason K. Blackburn and Jason A. Cooper
In response to increasing public demand for enhanced angling opportunities, Alberta Sustainable Resource Development (ASRD) initiated walleye stocking programs in the late 1980's and early 1990's on many irrigation reservoirs in southern Alberta, including the Crawling Valley Reservoir. Crawling Valley Reservoir was stocked each year from 1990 to 1992 and currently supports one of the most popular walleye fisheries in southern Alberta. However, little data exist on the population structure of walleye or angling pressure for this reservoir. To generate such data, the Alberta Conservation Association (ACA) and ASRD conducted a joint Fall Walleye Index Netting (FWIN) survey from 20 - 22 September 2004 to assess the status of the walleye fishery on the reservoir. Data on catch rate and population structure were obtained from gill net catches and growth rates were estimated using the von Bertalanffy growth model. Population status and stability were determined using an ASRD-derived regression model and the ASRD Walleye Management and Recovery Plan classification system.
A total of 221 walleye were captured during the survey, resulting in a catch rate of 27 fish/net/24 h or 25 fish/100 m2/24 h. Of the 144 walleye > 345 mm fork length (the size walleye reach first maturity in the reservoir), 96 were mature. The average catch rate of mature-sized fish was 15.8 fish/100 m2/24 h. Although nearly twice as many females as males were represented in the overall catch (sex ratio = 1.9 females:1.0 males), the sexes were equally represented among the 96 mature fish (sex ratio = 1.04 females:1.0 males). Overall, the size of walleye captured in 2004 ranged from 104 to 708 mm FL with an average fork length of 351 + 10.2 mm. The population exhibited a multimodal distribution with dominant modes at 110 - 140 mm, 200 - 230 mm and 380 - 510 mm. Thirteen age-classes were represented in the catch ranging from age-0 to 14 with a mean age of 5.2 + 0.3 y. Mean length-at-age ranged from 114.7 + 1.0 mm for age-0 fish to 559.1 + 14.0 mm for age-13 males and 634.7 + 32.9 mm for age-14 females. Dominant year-classes were 1997 (age-7), 1998 (age-6), and 2004 (age-0) with respective catch rates of 5.0, 5.0, and 5.1 fish/net/24 h. These classes comprised 58% of the total catch. In general, growth rates were higher for females than for males, although unpaired t-test results showed no significant difference in growth rate between the sexes except for age-13 individuals. Male and female fish reached first-maturity by ages-5 and 6, respectively. Estimates of growth rate derived using the von Bertalanffy growth model from data collected from 1998 to 2004 and mean length-at-age data from 1996 to 2004 indicated that annual growth of walleye has generally decreased over the years, suggesting an increase in fish density. One-way ANOVA tests among age-classes between sampling years also suggest a decrease in growth rates with significant decreases in mean length-at-age in five age-classes when compared to previous years. Walleye density including all size-classes was predicted at 15.03 fish/ha and 9.6 fish/ha for adult-sized fish. According to the ASRD Walleye Management and Recovery Plan classification system, the walleye population in Crawling Valley Reservoir is considered vulnerable. Accurate determination of whether a harvestable walleye surplus exists in Crawling Valley Reservoir depends upon a better understanding of the effects of incidental angling mortality, illegal harvest, and water availability on walleye population stability.