Wahleach Project Water Use Plan Wahleach Reservoir ... - BC Hydro

hydroacoustic surveys was used in order to reduce the equipment requirements and
effort necessary, but still allow for monitoring of the effects of fertilization on the
reservoir fish populations.
Gillnetting sampling sessions were completed in the spring of 2004 and 2005 (3 June
2004, 7 June 2004) and in the fall of 2006 (21 October 2006). A springtime gillnetting
session was planned for the end of June 2006 but was cancelled due to extremely
warm water temperatures. During each sampling trip, three sinking and three floating
gillnets were set in the Reservoir (Fig. 1). Each net consisted of panels of six different
mesh sizes (25, 89, 51, 76, 38, 64 mm stretch mesh) and in total was 28 m long and 2
m deep. All nets extended perpendicular from the shore. The floating nets were set
in 3 m of water and the sinking nets were weighted to the bottom to the 10 m contour.
Six baited Gee traps, baited with salmon roe, were also set in the evening and
retrieved in the morning (Fig. 1). The traps sat on the bottom in approximately 2 m of
water, a depth favored by sticklebacks. All gillnets and Gee traps were set in the late
afternoon, fished overnight, and were retrieved the next morning. The minimum set
time was 16 hours. Data from all nets were combined for calculation of mean catch
per unit effort (CPUE) by species. Individual nets were not treated as replicates.
Captured fish were identified using the Field Key to the Freshwater Fishes of British
Columbia (McPhail and Carveth, 1993), with weight (on an electronic balance, or a
Pasula spring scale for fish >600 g) and fork length recorded for each. Maturity
stage (immature, maturing, mature, spawning, spent, resting) was visually
determined from all kokanee, rainbow and cutthroat trout. Scale samples from each
kokanee were taken, processed, and read as described in Ward and Slaney (1988).
Scales were pressed into acetate and the imprint read under 30x magnification, with
age determined by counting annuli. Condition factors were calculated which was
defined as W/L 3 ·10 5 where W = weight in grams, L = fork length in mm. Aging data
for 2004 and 2005 are currently being processed and will be examined in future
reports.
3.9 Hydroacoustics
Hydroacoustic surveys have formed the basis of stock assessments in lakes and
reservoirs for many years. A survey was completed in late July which determined
stock distributions, size and abundance. A Simrad 120 kHz split beam echosounder
with a downward looking 7.0 degree transducer was employed to collect the survey
data. The transducer was towed along side of the survey boat at a depth of 0.5m,
survey data was collected at 2pps along transects lines and stored on hard disk of a
notebook computer. A Lowrance Sounder / GPS plotter was used to navigate along
11 predetermined transect lines at a boat speed of ~1.5m·s -1 , Fig. 5.
Split beam data was analyzed using Simrad EP500 version 5.3 processing software.
This software calculates fish density per hectare (fish·ha -1 ) and fish target strength
(TS) simultaneously by applying 20 and 40 log R Time Varied Gain (TVG) functions.
Wahleach Reservoir Fertilization Project, 2004-2006.
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