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Fish & Wildlife Main Page > Lake Stock Assessment Reports > Amanita Lake Recreational Fishery Stock Assessment 1999 Final Report
Introduction
This report presents the results of a stock assessment of Amanita Lake, completed on August 4, 1999 under a partnership arrangement between the Ministry of Environment, Lands and Parks and the Carrier Sekani Tribal Council (CSTC), with funding obtained from Fisheries Renewal B.C. through the Upper Fraser-Nechako Fisheries Council. Margo French and Lawrence Ward of the CSTC delivered the fieldwork component of the assessment; the author conducted the analysis and reporting of the field results. Inquiries pertaining to this report should be directed to the author at the email and address located at the bottom of this page. Amanita Lake is located approximately 69 km NE of Prince George, near McGregor Camp, on the north side of the Fraser River. A 10 vehicle-unit B.C. Forest Recreation Site is located adjacent to the lake, with car-top boat access to the lake's shore. A motor ban prohibits the use of motorized boats. In the past, the lake was heavily used as a recreational destination for hunters as well as workers from McGregor Camp. Prior to the camp's closure in 1996, the lake received over 10,000 user visits; more recently the usage has dropped to between 2,400 and 3,500 users per year. The proportion of users that target the lake specifically for angling is unknown, however anecdotal reports suggest that both summer recreationalists and fall hunters fish the lake to some degree. Click here for road directions to Amanita Lake. Amanita Lake was first surveyed in 1971, at which time it was determined that the lake was barren of all fish species. The lake was stocked with 16,000 rainbow trout fry in 1972, and in 1974 was stocked with 8,000 yearlings. The lake then received irregular releases of 10,000 fry until 1982, at which time the stocking rate was reduced to 5,000 and then 2,500 fish at various yearly intervals. In 1995 the number of yearlings stocked was reduced again, to 1,500 fish of the All-Female Pennask strain. A Habitat Improvement Reconnaissance Survey (Wightman, 1976) was conducted in 1975, with the stated intent "to investigate alternatives to continued stocking of this lake." This survey concluded that the lake did not contain any suitable spawning habitat, and that continued stocking would be required to sustain the lake's recreational fishery. In August 1990 a stock assessment was undertaken by Ministry staff, however the age structures collected during this survey were not analyzed, and management recommendations were not developed. Water quality data indicated that the lake's specific conductance was extremely low, at 7 µS/cm. This result was verified during a water quality sampling assessment that was undertaken by Queens University in 1997 (unpubl. data, note to file). Since none of the surveys completed to date had developed an age-structured analysis of the performance of fish stocked in Amanita Lake, and since no data had been collected since 1990, the lake was assigned a high priority for assessment in 1999.
Methods A 91.4 m sinking monofilament gill net of experimental mesh sizes was set in Amanita Lake at 1:00 PM on August 3, 1999, according to the methods specified in the Resource Inventory Committee document Fish Collection Methods and Standards. The net was deployed in a NW-SE orientation from the north shore of the western basin (Figure 1), and was retrieved on August 4 at 10:20 AM. The net was then re-deployed at 11:20 AM in a NW-SE orientation from the north shore of the lake's eastern basin, and was retrieved at 1:45 PM of the same day. The total combined soak time of the two net sets was 23.75 hours.
All trout collected were sampled for fork length (mm), weight
(to 0.1 g), sex, and maturity. Stomach contents were examined
in the field. Scales were collected for age structure analysis,
which was performed by Darlene
Gillespie of TimeMark Consulting Ltd. (Nanaimo, B.C.). Several
structures were assigned as both Age 2 and Age 1 by the contractor,
due to uncertainty in the ageing process. In this case the mean
lengths and weights of the two groups (i.e. tentative Age 1 vs.
confident Age 2) were compared using a one-tailed T test.
Results and Discussion CATCH SUMMARY The combined net catch yielded 18 rainbow trout (RB), for a catch per unit effort (CPUE) of 0.76 RB per net-hour. No other species were captured. See Appendix 1 for specific fish attribute data. Fourteen fish were classified as "immature," the remaining 4 were "maturing." Four fish were female, the gonads of all other fish sampled were not mature and could not be classified.
CONDITION The length-weight relationship of the sampled population is described by the equation W = 1 x 10-5 x L 2.99 (R2=0.98), where W = weight in grams and L = length in millimeters. For trout heavier than 100g, the mean condition of the population was 1.10, with a coefficient of variation of 14.5%. Since only 4 fish larger that 100 g were sampled, this statistic may not represent the population as a whole, however the mean condition reported is similar to that reported in other lakes in the region. No other deformities or health issues were reported. LENGTH FREQUENCY DISTRIBUTION and GROWTH Fish that were tentatively classified as Age 1 were significantly shorter and lighter than fish that were confidently assigned as Age 2 (length and weight : p < 0.01). It is therefore assumed that there were indeed Age 1 fish in the sample, and we postulate that Age 1, Age 2 and Age 4 fish were captured in Amanita Lake in 1999 (see Appendix 1). These trout are represented by two distinct size groups, as seen in Figure 3.
According to the Provincial stocking records database (see Appendix 2), and assuming that natural recruitment is inhibited, Amanita Lake had a trout population that was composed of 1, 2, 4 and 5 year old fish in 1990. This age structure is supported by the length frequency distribution observed for that year. The lake has been stocked yearly since 1989, yet in 1999 the sampled population did not include any fish from the 1996 (i.e. Age 3) year class. This absence could be explained by the occurrence of a year class failure, by an error in compiling the stocking records, or due to sampling error. Age 1 fish gained an average of 8.8 g from June 4 to August 4 in 1999, and Age 2 trout gained an average of 25.3 g from May 31, 1998 to August 4, 1999. The largest fish captured was a 375 g, 4-year-old female that was 327 mm in length. The mean weight and length of the 4-year-olds sampled was 330 g and 311 mm respectively. Assuming a minimum acceptable catchable size of 250 mm, Amanita Lake rainbow trout currently do not enter into the recreational fishery until they have reached at least 3 years of age.
Management Recommendations Amanita Lake was stocked in order to create a "put and take" recreational fishery of low to moderate use for area residents (note to file, 1989). While it was recognized that the lake would not likely produce large rainbow trout, it was initially assumed that the lake had a TDS of 100 mg/L and stocking densities were based on this assumption. Recent survey results (Anonymous 1990, Bruce Carmichael, MELP Water Quality Biologist, pers. comm.) have shown that Amanita Lake has the lowest conductivity of all lakes sampled in the Omineca region, and it is now estimated that the lake's TDS is actually between 4 and 8 mg/L. While not spectacular, the rate of growth recorded for 4-year-old rainbow trout during our survey was actually higher than would be expected at current stocking densities, given the lake's low productivity. The provincial stocking formula (# yearlings = TDS * ((2.47*Shoal Area) + (0.247*Surface Area)) recommends that Amanita Lake be stocked at 411 yearlings per year, far below the current stocking rate. The growth rate of Amanita Lake fish is therefore not likely to be directly linked to the lake's TDS but rather to other factors that have not been accounted for. The very low rainbow trout catch per unit effort recorded during this assessment suggests that the lake contains few catchable trout. In addition, the complete absence of the 1997 year class is cause for concern, and it is possible that the low productivity may have contributed to a year class failure. Due to the combination of relatively slow growth and low densities of catchable trout, Amanita Lake may not be considered as a high quality angling experience by recreationalists. However, the statistics indicate that the Recreation Site is highly used by the public, suggesting that at least some users are targeting the lake as an angling destination. To gain a better understanding of angler use (as opposed to Recreation Site use), it is recommended that angler interest be assessed through informal interviews with Recreation Site users, local residents, and area workers. If the results of these interviews reveal that the lake is valued by the angling community, then stocking should continue, as its relative cost to the Fisheries program is fairly minimal.
Literature Cited. Anonymous, 1990. Amanita Lake stock assessment data. Data
on file. Ministry of Environment. Prince George.
For More Information: Contact :Ted Zimmerman
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