PHOTO 1. View of Witney Lake, August 1999 Click image to view 54K JPG

PHOTO 2. Roadside View of Witney Lake, August 1999 Click image to view 76K JPG

Introduction

This report presents the results of a stock assessment of Witney Lake, completed on August 13, 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 directions to Witney Lake.

Witney Lake was initially surveyed in 1981 and was found to contain rainbow trout, lake chub, and longnose suckers, based on gill net and minnow trap surveys at that time. The lake was subsequently stocked in 1982 with rainbow trout fall fry, and has since received intermittent fall releases. The stock schedule for Witney Lake mirrors that of Portal Lake, however the density of fish stocked in Witney is an order of magnitude less than Portal, at 320 per hectare.

A follow-up survey was conducted in 1985 (Philip) to investigate the status of the stocked fishery and to resample certain biophysical attributes initially measured during the 1981 survey. However, time constraints precluded the deployment of gill nets and minnow traps, so the crew engaged in 30 minutes of angling as an alternate sample technique. No fish were captured using this method.

Since the 1985 survey, a variety of stocking alternatives (i.e. fall fry vs. yearlings, annual vs. alternate year stock schedules) have been employed on Witney Lake. To date, these alternatives had not been systematically evaluated. Witney Lake was therefore assigned a high priority for assessment in 1999.

Methods

FIGURE 1. Location of Witney Lake gill net sets, August 11 to 13, 1999. Click image to view full bathymetric map. Click image to view 26K GIF

An experimental, 91.2m sinking monofilament gill net was set in Witney Lake on August 11, 1999 according to the methods specified in the Resource Inventory Committee document Fish Collection Methods and Standards. The net was deployed at 1:45 PM and retrieved August 12 at 11:40 AM. Only one fish was captured after this period, so the net was redeployed 12:45 PM at a different site (Figure 1). This second net set was retrieved on August 13 at 10:00 AM, for a total combined soak time of 43.17 hrs.

Set 1 was positioned from the north shore and extended in a N-S orientation, to an anchor depth of 6.75 m. Set 2 was positioned off the southwest shore and extended in a NNE orientation, south of the first set. The second set ranged in depth from the surface to approximately 7 m. The depths noted by the field crew in 1999 were deeper than the maximum depth reported for the lake in 1981. This anomoly may be attributable to a deepening of the lake since the original survey date, or to measurement error in 1999. No reference was made to the benchmark established in 1981, which was located 2.5 m above the water surface at that time.

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

Water temperature and a Secchi disk reading were also reported.

Results and Discussion

CATCH SUMMARY

The combined net catch yielded 3 rainbow trout (Table 2), 63 longnose suckers, 6 burbot, and 3 lake chub. The catch per unit effort (CPUE) was 0.07 rainbow trout per net-hour.

The low catch rate for Witney Lake rainbow trout is not surprising, considering that only 2,500 fall fry were stocked in each of the last three stocking events, and that prior to the 1998 fall stocking the lake was last stocked in 1995. The combination of low stocking rates, natural and fishing mortality of the now four-year-old 1995 cohort, and the co-occurence of burbot (a piscivorous species) are likely responsible for the low catch rates recorded. The absence of yearlings (i.e. those stocked in 1998) may be attributable to their slow growth, thereby being too small to recruit to the sampling gear.

Management Recommendations

PHOTO 3. Rainbow trout captured in Witney Lake, August 1999. Click image to view 75K JPG

With only 3 fish sampled in 1999, and none captured in 1985, there is little data available on which to base management recommendations for the Witney Lake fishery. The fact that 6-year-old fish up to 980 g exist in Witney suggests that growth is sufficient, but not extraordinary, to support recreational fishing. Whether these fish constitute hatchery stock or are of wild origin is unknown, however the lack of younger age classes in the sample suggests that natural recruitment is low to negligible.

Since the gill net catch per unit effort in 1999 was very low, it is reasonable to assume that current angling success is poor. The sporadic stock schedule that has occurred to date may be insufficient to provide enough fish for a successful angling experience on Witney Lake, especially considering that the lake is located immediately off Highway 16 in Mt. Robson Provincial Park, where frequent use by anglers would be expected. In order to develop the most appropriate management strategy for Witney Lake, the following actions are recommended:

• data on current angling pressure (anecdotal or otherwise) should be obtained;

• stocking rates should remain consistent for at least a four year period in order to evaluate stock rates and fishery performance; and

• a followup assessment, targeting adults only, should be completed once consistent stocking has been implemented over a four year period

In the interim, the Ministry will continue to stock 2,500 fall fry in alternate years into Witney Lake. A repeat of this assessment should then be conducted in August 2001, at which time the 1998 cohort will be available to the sample. Sampling during this time will provide data on the relative density and mean growth rate of trout that have been stocked at a consistent level. This data can then be used as the basis to make decisions regarding stocking options and/or harvest rates should they be deemed necessary.

Literature Cited

Miller, C. and B. Tupniak. 1981.  Witney Lake : Lake Survey Data. Report prepared for the Fisheries Branch, Ministry of Environment. Prince George.

Philip, D.F. 1986.  Witney Lake - Stock Assessment August 13,14, 1985. Report prepared for the Fisheries Branch, Ministry of Environment. Prince George.

Appendix 1.

For More Information:

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