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A biological study of the influence of the Bridge River rapids on the sockeye runs of the Upper Fraser watershed Killick, Stanley Reginald

Abstract

The significant of obstructed passage of sockeye up the Fraser river was not realized fully until the very disastrous effect of Hell’s Gate were revealed by the International Pacific Salmon fisheries Commission in 1941. After the importance of the Hell’s Gate obstruction was established, evidence on the conditions at the Bridge River Rapids were reviewed and a study commenced in 1942. These Rapids are located on the Fraser River, 76 miles north of Hell’s Gate and must be passed by all of the sockeye races destined for the upper Fraser watershed. The Rapids consists of two separate falls, and have been reported to have caused difficult and block passage to salmon as early as 1912. The study, commenced by the Commission in 1942, was outlined to determine the direct influence of the Rapids on the current sockeye populations and to make such adjustments in the contour of the Rapids as to allow unobstructed passage of salmon at all water levels, should blockade conditions be revealed. The problem involved four separate tagging experiments from 1942 to 1946. No tagging was done in 1943. The results of the various experiments revealed that the sockeye were delayed or seriously blocked in some years during low water levels occurring in September and October. The late-running Chilko and Stellako sockeye were the only races that were effected as the other runs to the Stuart, Bowron and Horsefly districts passed through the Rapids early in the summer when the water levels were high. After the completion of the analysis of the tagging experiments up to 1945, a recommendation, that two fishways be constructed at the Rapids, was submitted for the consideration of the Commission. The installation of fishways was approved and their construction complete for the salmon runs of 1946. The efficiency of the fishways was tested in that year and a complete change in the pattern of the tag recoveries was recorded. Whereas, block conditions were previously shown by sudden increases in the number of tags recovered below the Rapids; practically no tags were recovered below during low water periods after the fishways were built. The same methods of analysis that were used to determine block conditions were repeated in 1946 to test the fishways and in each case a noticeable improvement in passage was recorded. Therefore, it was concluded that the fishways built at the Bridge River Rapids were successful in passing sockeye salmon through the preciously known block periods that were revealed by tagging in 1942, 1944, 1954.

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