Fisheries and Oceans :;hes et Oceans 1330 80 Sixth Street New Westminster, BC V3l 5B3 You' "", Votreterenc December 22, 1987 Mr P M Br d'y Director, ater Management Ministr of Environment 765 Br ughton Street Vict ia, BC Y8Y 1X5 Branch ' 7 _ Dear Sir: Re: WATER RELEASES FROM OKANAGAN LAKE FOR SOCKEYE SALMON r As you are aware, drought conditions in the Okanagan lake region this year have resulted in lower than normal lake elevations and this poses a threat to the eggs of beach spawning kokanee n November 1987, CJ Bull, Fish and Wildlife, had requested that the present lake discharge of 175 cfs into the Okanagan River be reduced to 100 cfs This would reduce the winter drop in lake elevation from 6 inches to 35 inches, thereby reducing the dehydration and freezing risk to kokanee eggs by up to 30% To address this problem, a survey was carried out November 1920 to determine what flow release from Okanagan lake would allow Okanagan lake kokanee downstream and Okanagan River sockeye eggs to share the same risks of dewatering and/or freezing " Two sites were chosen to resolve the problem; a prime kokanee beach spawning site at Carrs Point on Okanagan lake, north of Kelowna, and a representative sockeye spawning area on the Okanagan River near Oliver The beach at Carrs Point had a gentle slope of 1:227 Flow releases from the Yaseux Lake dam were manipulated lowered to 100 cfs for 16 hours to measure the areal extent of exposed sockeye redds at 175 cfs and 100 cfs This survey indicated that if the discharge of Okanagan Lake is reduced from 175 cfs to 150 cfs the egg loss by dewatering and/or freezing will be shared equally by kokanee and sockeye salmon with each stock having 7 million eggs at risk r'1_2rl1
2 n view of our decision to cooperate with Fish and Wildlife and balance or equalize the rate of mortality of kokanee and sockeye eggs, it is recommended that the discharge from Okanagan lake be temporarily reduced from 175 cfe to 150 cfs until winter inflow (December to March) balances or reverses the present downward trend in Okanagan lake elevation This information was passed on to D Narver two weeks ago and it is my understanding that this adjustment to the river flows was to be implemented at that time This memorandum and attached field report will confirm the position we have taken on this flow problem Yours truly, OE Langer Head, Habitat Fraser River, and Yukon Management Unit Northern BC Division WFlcs WF1/Brady Attachment cc: C Bull D Narver F Fraser B Kurtz G Kosakoski B Zook D Deans '
1+ (boerrment 0( Canada Gowemement du Canada MEMORANDUM t\; fe DE SERVCE SECURTY CLASSFCATONDE SCURTE Tft OE Langer L OURFLE N R FRENCE FROM DE YOUR FLE V RF RENCE L WJ field cember 18, 1987 SUBJECT OBJET DETERMNATON Of now N THE OKANAGANRVER THAT WLL ALLOW KOKANEE AND SOCKEYE EGGS TO SHARE EQUAllY THE RSK Of EXPOSURE TO DROUGHTCONDTONS The request by fish and Wildli fe to reduce flows in the Okanagan River from 175 cfs to 100 cfs for the purpose of reducing the risk to kokanee eggs along the shore of Okanagan Lake was the subject of an onsite meeting on November 19, 1987 The meeting at Oliver was attended by CJ Bull, fish and Wildlife, fishery Offlcer S Coultish, C Edge, Water Management and W field, Habitat Management Two survey sites were selected (by mutual agreement) on the Okanagan River near Oliver (see location map) The first site, 27 km downstream from the Highway 97 bridge crossing, was used to monitor river discharge by flow metering (figure 1) The second site, 31 km downstream from the bridge, was used for mapping the channel bed and surveying the elevation of redds above and below the water surface The second site was an area of channel measuring 310 feet long and 90 feet wide (figure 2) that would serve to represent the increase in the exposure of river gravel with decreasing channel flow in the Okanagan River " During the afternoon of November 19, the flow was metered at 180 cfs and the area of exposed gravel (redds) was found to be 8% (Table 1) of the total site area of 27,000 ft2 At 4 pm the discharge from Vaseux lake dam was reduced to 100 cfs overnight The next day at 9 am, the flow water was metered at 131 cfs and the area of exposed gravel increased to 22% of the site area from the metering data and survey results, it was estimated that all redds would be covered by water at 240 cfs (figure 3) Assuming a uniform distribution of redds in the river gravel, a river discharge of 150 cfs would expose 16 of the redds to the direct effects of drying and/or freezing According to Bill Zook, Washington Department of fisheries, a reliable count of 35,000 sockeye spawners moved upstream in the /2
2 Okanagan River above the Similkameen confluence An estimated 1,OOO of these are above Drop Structure '13 at Oliver f the flow in the Okanagan River is maintained at 150 cf and 17,500 sockeye st 2,500 eggs/fish produce 43,7O,OOO eggs, a 10s8 of 16 of the redds trsnslates into a loss of 7,000,000 eggs These results sre summarized in the following table: TABLE 1 OKANAGAN RVER Discharge (efs) 240 180 160 150 135 100 o Area exposed () NL 8 13 16 225 36 100 Number of eggs at risk NL 3,500,000 5,687,500 7,000,000 9,843,70 15,750,000 43,750,000 Currently, 175 efs is released from Okanagan Lake for sockeye salmon in the Okanagan River and this discharge, with no winter inflow, will lower the lake elevation by 6 inches during the period December to March inclusive BC Fish and Wildlife has requested that the discharge be reduced to 100 cfs in order to reduce the drop in lake elevation to 35 inches which, they estimate, would save 30% of the eggs or 7 million eggs According to the 1987 escapement estimates, 75% (T able 2) of the spawning took place along the lake shore, leaving 25 for stream spawning Studies show (Table 3) that an average of 335% of the eggs are deposited very close to shore at depths ranging from 0 to 05 feet TABLE 2 KOKANEE ESCAPEMENTS OKANAGAN LAKE (x 1,000) " Year Stream Shore Percent Spawning Spawners Spawners on Shore 1977 1978 59 153 545 54 57 26 1979 203 108 35 1980 1981 148 113 180 214 55 65 1983 69 55 44 1984 152 5 3 1985 205 29 12 1986 87 17 16 1987 55 165 75 /3
) TABLE ) KOKANEE EGG DEPOSTON BY DEPTH According to Matthews and Bull (1981) and Halsey and lea (1973) Water Depth (ft ) Matthews/Bull Percent of HaEQs sey/lea 005 0510 1015 1520 2025 23 53 60 78 100 44 62 79 96 100 On November 20, the slope of the beach at Carrs Point, a prime kokanee spawning area on Okanagan Lake, was surveyed and found to be 1:227 (figure 4) n 1987, 82,500 kokanee deposited 25 million eggs along the shoreline or 303 eggs/female f, for example, the lake discharges at 175 cfs during the next four months, the lake drawdown of 6 inches (figure 5) wi 11 expose the kokanee redds at lake depths between 0 and 05 feet and place some 84 million eggs or 34 of the total spawn at risk f the lake discharge is reduced to 100 c fs the drawdown of 35 inches wi 11 expose redds at depths from 0 to 029 feet and place some 5 mi 11 ion eggs or 20 of the total spawn at risk Table 4 is a summary of risks to kokanee and sockeye spawners at various flows in the Okanagan River TABLE 4 Okanagan River Discharge (cfs) Okanagan Lake Drawdown Cinches) Eggs Exposed (Millions) Kokanee Sockeye (82,500 fem) (17,500 fem) Shore spawning River spawning 100 135 140 145 150 155 160 165 170 175 35 46 48 50 52 53 55 565 585 60 50 64 67 70 72 74 77 79 82 84 158 98 83 74 70 61 57 53 46 35 /4
4 According to Table 4, the risk to koksnee should approximate the risk to sockeye eggs if the discharge from Okanagan lake is 150 cfs Under the present flow regime, a flow reduction from 175 cfs to 150 cfs will result in a loss of some 7 million eggs each; ie the kokanee will lose 29 of the run and the sockeye will lose 16 of the run The possibi i ty of the fall drought extending through the winter months is considered remote The last winter drought (November February) when no lake inflow occurred was during the winters of 1929, 1930 and 1931 n recent fears, low winter inflows have been recorded, ie 1962 6,000,000 m, 1979 8,000,000 m3 To put this into perspective, 1/10 of an inch of rain falling in one day on the Okanagan Lake surface of 84,200 acres will produce 7017 acre feet of storage which is sufficient to supply an extra 10 cfs of discharge for 35 days Any rainfall will work to the advantage of the kokanee eggs by slowing the rate of drawdown of Okanagan Lake n view of our decision to balance or equalize the rate of mortality of kokanee and sockeye eggs, at 7 million each, it is recommended that the discharge from Okanagan lake be temporarily reduced from 175 cfs to 150 cfs until winter inflow (DecemberMarch) balances or reverses the downward trend in Okanagan Lake elevation wrlcs wr1/kokanee " Attachment
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