SPAWNING ESCAPEMENT OF OKANOGAN RIVER 

 BLUEBACK SAI/<ON (ONCORHYNCHUS NERKA) , 1957 



The encroachment of civilization has 

 greatly restricted the spawning migrations 

 of the Columbia River blueback salmon. 

 The Osoyoos, Wenatchee, and Redfish Lake 

 systems are the only spawning and rearing 

 areas of importance remaining available to 

 this valuable species of Columbia River 

 S6uLmon> 



The spawning area of the Okanogan, 

 which is the most important of the three 

 systems, has been channelized recently in 

 connection with a Canadian flood-control 

 project. This channelization necessitated 

 construction of 13 drop structures (small 

 dams with 3 feet of head) which the salmon 

 must ascend on their migration from Lake 

 Osoyoos to the spawning area. Annueil sur- 

 veys have been made to detenaine the im- 

 mediate effect of the flood-control work 

 on the salmon and to see that all steps 

 necessary for their protection are taken. 

 The long-range effect of this project on 

 the Okanogan blueback runs will not be 

 known for several years. 



SURVEYS 



Blueback spawning activities in the 

 Okanogan have been surveyed extensively 

 each year since the flood-control project 

 started in 1951. Five surveys were made 

 this season in much the same manner as in 

 previous years. The 1957 surveys were of 

 particular interest because for the first 

 time the fish have had to ascend the new 

 channel with its 13 drop structures. Since 

 a partial block existed at drop structure 

 No. 2 during the last half of September, 

 special attention was given to the spawn- 

 ing success of the migrants. This delay 

 plus the possibility of other delays could 

 cause the fish to arrive at the spawning 

 area too late and too weeik for successful 

 spawning. 



The section designations used in 

 pluvious years were followed closely. These 

 sections and the location of the drop 

 structures ajre depicted in figure 1 (page 

 2). Conditions for observing the spawners 

 were very good except on October 22, when 

 wind and snow made observations difficult. 



The area from the Southern Okanogan Lands 

 Project Dam to drop structure No. 13 was 

 surveyed by rubber boat, and the area from 

 drop structure No. 13 to Lake Osoyoos was 

 checked from the dike paralleling the river. 

 A few spawning fish were observed near drop 

 structures No. 6 and No. 13, but the spawn- 

 ing below No. 13 was of little importance. 



SPAWNING ESCAPEMENT 



Table 1 presents the actual counts 

 made on the various surveys and table 2 

 shows the spawning population estimate 

 derived by the "Factor 5" method. This 

 method (Gangmark and Fulton 1952) has been 

 used on the Okanogan for several yeeirs. 

 Although we are convinced that it gives a 

 consistently low estimate, we feel that it 

 serves as a reliable index of the magnitude 

 of the spawning population. 



The 1957 count of blueback through 

 the fishways at Rock Island dam was 71,261. 

 Of these, 28,231 were counted at Tumwater 

 Dam on the Wenatchee River, 8ll were taken 

 by "up river" hatcheries and miscellaneous 

 samples, and an estimated 3>017 were taken 

 by the Okanogan Indian fishery. The 

 "Factor 5" estimate of 25,350 for the 

 Okanogan spawning population leaves 13,919 

 fish or 19.5 percent of the Rock Island 

 blueback count unaccounted for. Table 3 

 is a record of the distribution of blue- 

 back above Rock Island obtained by using 

 "Factor 5" estimates for the Okanogan. 

 The increasing number of fish accounted 

 for in recent years is probably due to 

 improved siirvey techniques euid accurate 

 counts obtained at Tumwater Dam. 



WATER TEMPERAIURE 



Although it has not been proved, 

 many of the fish unaccounted for may have 

 succumbed to the effects of the high 

 temperatures encountered in the Okanogan 

 during the migration period (fig. 2). For 

 more than 2-1/2 months during July, August, 

 and September, the river temperature was 

 well above the 65 "F. level. These high 

 temperatures are common since the four 



