TRANSPORTATION OF CHINOOK SALMON , ONCORHYNCHUS TSHAWYTSCHA , AND STEELHEAD , SALMO GAIRDNERI , SMOLTS IN THE COLUMBIA RIVER AND EFFECTS ON ADULT RETURNS

Chinook salmon, Oncorhynchus tshawytscha, and steelhead, Salmo gairdneri, were captured at Little Goose Dam in the Snake River during their seaward migration and transported 400 km downstream to the lower Columbia River below Bonneville Dam. Their survival was increased from 1.1 to 15 times as compared with control fish which passed by seven mainstem low-level dams and reservoirs. Variations in survival were mainly dependent on species and environmental conditions in the river during the period fish were transported. The homing ability ofthe adult fish was not significantly diminished; less than 0.2% of strays occurred among adult returns from groups transported. Transportation did not affect ocean age or size of returning adult steelhead, but ocean age of returning adult chinook salmon may have been affected. Steelhead returned to Little Goose Dam at a substantially higher rate (1.4-2.7%) than chinook salmon (0.1-0.8%) from groups transported. The timing of adult returns of both species to Little Goose Dam was not related to the time of capture and downstream release of smolts. Salmonid populations of the Snake River and its Idaho tributaries have declined rapidly in recent years to the point that the very survival of some stocks is threatened. The total run (i.e., catch plus escapement) of chinook salmon, Oncorhynchus tshawytscha, attributable to the Snake River dropped from 120,000 adults in 1972 to 50,000 in 1974 (Raymond 1979). Similarly, the total run of steelhead, Salmo gairdneri, an anadromous form of rainbow trout, declined from 100,000 adults in 1972 to below 20,000 in 1974. The downward trend ofthe anadromous salmonid popUlations has been ascribed to losses ofjuvenile migrants at the series ofeight dams (Figure 1) and associated reservoirs in the Snake and Columbia Rivers through which the smolts must pass on their way to the sea (Raymond 1979). With the goal of protecting the migrants from the hazards of dams, a system for transporting smolts around the dams was investigated by the National Marine Fisheries Service. The juvenile migrants were collected from the Snake River at Little Goose Dam (the uppermost dam-Figure 1), transported around the entire series of dams, and released below Bonneville Dam (the lower­ lNorthwest and Alaska Fisheries Center, National Marine Fisheries Service, NOAA, 2725 Montlake Blvd. E., Seattle, WA 98112. Manuscript accepted December 1979. FISHERY BULLETIN: VOL. 78, NO. 2,1980. most dam)' on the Columbia River. The effects of such transportation on the survival and catch of the fish and on the ability of the adults to "home" to their natal streams must be known if fishery agencies are to evaluate the transportation sys­ tem as a practical means of protecting Snake Ri ver salmonid runs. The main objectives of the research at Little Goose Dam were: to determine the effect of transportation on homing and survival of juvenile chinook salmon and steelhead collected at Little Goose Dam and released at two locations downstream from Bonneville Dam and to compare these results with an earlier study done at Ice Harbor Dam (Ebel et al. 1973) where fish were FIGURE 1. -Transportation routes and release location of exper­ imental chinook salmon and steelhead collected and marked at Little Goose Dam, 1971-73.