Recreational Fishery Stock Assessment 1999 Final Report

PHOTO 1. Ferguson Lake Aerial Photo. June 2001. Click image to view 71K JPG

Introduction

This report presents the results of a stock assessment of Ferguson Lake, completed on August 17, 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. Field activities were carried out by Margo French and Lawrence Ward of the CSTC. Analysis and reporting of the field results were conducted by the author. Inquiries pertaining to this report should be directed to the author at the email and address located at the bottom of this page. Click here for road directions to Ferguson Lake.

Ferguson Lake was initially surveyed in 1982 and was found to support lake chub and longnose suckers at that time. The lake was subsequently stocked in 1984 with 5,000 eastern brook trout, then after a 2 year hiatus was stocked again with 5,000 fish in both 1987 and 1988. The stocking rate was reduced to 2,500 fish per year and with the exception of 1997 (2,000) and 1993 (2,900), has since remained at that level. Further details of the stock history of Ferguson Lake can be found in Appendix 2.

A follow-up stock assessment was conducted by the Ministry in 1990 (Barry, unpublished data), which confirmed that the stocked brook trout were growing to 620 g. No further work had been completed since this survey, and as such Ferguson Lake was assigned a high priority for assessment in 1999.

FIGURE 1. Location of Ferguson Lake gill net set, August 16-17, 1999. Click image to view 27K GIF

Methods

An experimental, 91.2m sinking monofilament gill net was set in Ferguson Lake on August 16, 1999 according to the methods specified in the Resource Inventory Committee document titled Fish Collection Methods and Standards. The net was deployed at 10:25 AM and retrieved on August 17 at 9:25 AM, for a total soak time of 23 hrs. The net was set from the west shore, directly across from the lake's access road, and extended in an E-W direction (Figure 1) from the surface to a maximum depth of 5.0 m.

All trout collected were sampled for fork length, weight, sex, maturity, and stomach contents. The general condition of the fish sampled was also recorded. Fin ray sections were collected for age structure analysis, which was performed by Darlene Gillespie of TimeMark Consulting Ltd. (Nanaimo, B.C.).

Water temperature, weather conditions, and a Secchi disk reading were also reported.

Results and Discussion

CATCH SUMMARY

The net catch yielded 7 eastern brook trout (EB) and 48 longnose suckers, for a catch per unit effort (CPUE) of 0.3 EB per net-hour. In 1990, a 23.5 hour set yielded 10 EB for a CPUE of 0.43 EB per net-hour. Brook trout captured in 1999 were on average larger and heavier than those sampled in 1990 (Table 1), with the largest fish reaching 1400 g in 1999. The mean condition remained the same for both years. See Appendix 1 for the complete 1999 brook trout sample data. Five of the seven brook trout sampled in 1999 were classified as "maturing", one could not be classified and one was immature.

CONDITION

FIGURE 2. Length vs. weight of brook trout captured in Ferguson Lake, August 17, 1999. Click image to view 4K GIF

The weight of brook trout increased according to the equation W = 7x10^-6 x L^3.097 (R²=0.99), where W = weight in grams and L = length in millimetres. This relationship is expressed in Figure 2. The small number of adults sampled precludes an in-depth analysis of the health of Ferguson Lake brook trout, however there were no anomolies noted in the length-weight relationship.

FIGURE 3. Age vs. length of brook trout in Ferguson Lake, August 17, 1999. Click image to view 4K GIF

GROWTH

Figure 3 shows the length-at-age relationship for brook trout sampled in Ferguson Lake in 1999. While the sample size is small, it is evident that the fishery is producing brook trout up to 48 cm and 1400 g by 4 years of age at present stocking levels. At this growth rate, it is likely that stocked brook trout are reaching a catchable size by Age 2 (i.e. minimum 25 cm).

The one yearling which was sampled in 1999 was part of the cohort released into the lake on May 28, 1998 at a mean weight of 4.3 g. If the sampled individual is representative of its age class, this cohort has exhibited a growth rate of approximately 14.5 g over a 64 week period.

Management Recommendations

The catch rate of brook trout in 1999 was low but comparable to that recorded during the 1990 survey. The present assessment was completed in late summer, at which time the surface water temperature was 18.5°C. Since brook trout tend to avoid warm conditions, the Ferguson Lake population may have been residing below the lake's thermocline, in a relatively inactive state.

The fish that were caught consist of well conditioned, healthy individuals with no obvious deformities or health problems. The observed growth rate of the sampled brook trout suggest that stocked fish are recruiting into the recreational fishery at about 2 years of age, with 4-year-old fish attaining lengths of at least 480 mm. It would therefore appear that current stocking rates are sufficient to support a modest recreational fishery, with the potential for a satisfactory angling experience. Additional data describing the extent of angler use on Ferguson would prove valuable in the interpretation of the fishery performance statistics.

Five of the fish captured were classified as "maturing", however four of these were male. Since 1996 Ferguson Lake has been stocked with triploid (3n) fish which are reproductively sterile, although male 3n trout are known to develop secondary sexual characteristics. While inconclusive, it is possible that the 4-year-old (i.e. 1995) cohort is reproductively viable. However, evidence of naturalization of Ferguson Lake brook trout is so far non-existent and the risk of natural recruitment is probably low. Nonetheless, any future work done on Ferguson Lake should address the naturalization issue.

Literature Cited

Little, 1982.  A reconnaissance survey of Ferguson Lake. Report prepared for the Fisheries Branch, Ministry of Environment. Prince George.

Appendix 1.
Appendix 2.

For More Information:

Contact :Ted Zimmerman
Sr. Fisheries Biologist, Omineca sub-Region
Prince George, B.C.
250-565-6852