Introduction

This report presents the results of a stock assessment of Byers Lake, completed on August 27, 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 Gary George 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.

Byers Lake is one of five stocked lakes that are managed within Eskers Provincial Park, located 33 km northwest of Prince George. The lake was initially surveyed in 1985 and was determined to be barren of fish based on gill net and minnow trap surveys at that time. The lake was subsequently stocked in 1988 and 1989 with eastern brook trout fingerlings, after which stocking was ceased at the request of the Parks Branch. The cessation of stocking was brought about due to concerns regarding uncontrolled angler access to the lakes, which was occurring in response to the stocking program but in advance of the completion of adequate infrastructure to support the increased traffic.

After the stocking program ceased, unconfirmed reports were submitted to Fisheries and Parks staff that some of the lakes were continuing to produce brook trout, presumably through natural recruitment. Reports were also received that indicated that fish may have been transferred between lakes, a situation which, if true, would have a direct bearing on the management objectives for each of the lakes initially stocked. In 1996, Parks Branch requested that the stocking program be reinvoked, as it was felt that angler use could now be controlled given the state of the park's infrastructure. The lake was accordingly stocked in 1997 at an alternate-year stocking frequency.

Since no assessments had been done on any of the lakes since stocking was initiated in the late 1980s, and since the renewed stocking program had been in effect for two years, Byers Lake was assigned a high priority for assessment in 1999.

Methods

FIGURE 1. Location of Byers Lake gill net set, August 27, 1999. Click image to view full bathymetric map. Click image to view 37K GIF

A 91.4 m sinking monofilament gill net with experimental mesh sizes was set in Byers Lake on August 26, 1999, according to the methods specified in the Resource Inventory Committee document Fish Collection Methods and Standards. The net was deployed at 3:00 PM and retrieved August 27 at 11:00 AM, for a total soak time of 20 hours. The net was set from the south shore near the east end of the lake, and extended in a NNW orientation. The net ranged in depth from the surface to approximately 9 m. (Figure 1).

All trout collected were sampled for fork length, sex, and maturity. Weight was measured from a sub-sample of the fish surveyed, and was collected to the nearest 100 g. Fin rays were collected for age structure analysis. This analysis was performed by Darlene Gillespie of TimeMark Consulting Ltd. (Nanaimo, B.C.).

Results and Discussion

CATCH SUMMARY

The net catch yielded 24 eastern brook trout (EB), for a catch per unit effort (CPUE) of 1.2 EB per net-hour. The complete data set can be viewed in Appendix 1. Seven of the 24 brook trout sampled were classified as "immature" and their sex could therefore not be determined. Of the remaining 17 fish, 1 was classified as a mature male, and the remaining were either not sampled or were classified as "unknown". Since 1997, the brook trout released in Byers Lake have been of triploid origin, which are permanently immature so as to prevent natural recruitment for this introduced species. The single mature male that was sampled is likely the progeny of the 1988 or 1989 stock, which were fully viable and therefore capable of reproduction.

CONDITION

A condition assessment cannot be completed for this data set since only a sub-sample of the fish that were captured were weighed. Additionally, weight was only measured to the nearest 100 g, thereby precluding an accurate analysis of the fish that were sampled.

FIGURE 2. Length frequency distribution of brook trout captured in Byers Lake, August 27, 1999. Bold numbers indicate age of size class. Click image to view 5K GIF

LENGTH FREQUENCY DISTRIBUTION and GROWTH

The length frequency distribution (Figure 2) of the catch shows that the population was dominated by 160 - 200 mm 2-year-old sub-adults, which were stocked into Byers Lake as finglerings on June 17, 1997, at a mean weight of 3.01 g (Appendix 2).

The remainder of the 1999 catch consisted of a single 4-year-old adult brook trout, (Figure 3) which weighed 1600 g and was 455 mm in length. This individual is likely the progeny of the viable population that was stocked in 1989 (see below).

At 185 mm, the mean growth rate of 2-year-old brook trout was not as rapid as that observed in Bow Lake or Butterfly Lake, both of which received identical stocking treatments to Byers. The age structure of the larger fish sampled was not analyzed by the ageing contractor as its fin ray was cut too far from the base of the fin. Its age has been estimated at 4 years, but it has not been included in the growth analysis.

Management Recommendations

FIGURE 3. Brook trout sampled at Byers Lake, August 27, 1999. Click image to view 55K JPG

Byers Lake is more productive (TDS=140 mg/L) and has a much larger surface and shoal area relative to Bow and Butterfly lakes. These attributes suggest that the growth rate of brook trout in Byers Lake should equal or exceed that determined for the latter two lakes, since the stocking treatments for all three lakes have been identical. However, the survey data suggests that the opposite situation exists, whereby growth of 2-year-old fish in Byers Lake is slower than that recorded in the other lakes. This seemingly contradictory finding supports a recommendation for additional sampling in Byers Lake.

The presence of the 4-year-old brook trout suggests that some limited natural recruitment may have occurred in the past. Alternatively, this fish may have been part of an illegal transfer of brook trout from another lake in the park. Regardless of its origin, the extent of natural recruitment in Byers Lake appears to be limited and is not likely to be a cause for concern.

The current stocking plan for Byers Lake calls for 3000 fingerlings to be stocked at an alternate year frequency. This schedule should be adhered to until such time as additional growth data can be obtained from Byers Lake. A follow-up sample in the summer of 2000 would substantiate the results of the 1999 survey, and may provide some insight into the anomolies noted in this study.

Literature Cited

Philip, D.F. 1985.  A Reconnaissance Survey of Byers 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