INFLUENCE OF ROCKY REACH DAM AND THE TEMPERATURE OF THE 

 OKANOGAN RIVER ON THE UPSTREAM MIGRATION OF SOCKEYE 

 SALMON 



By Richard L. Major and James L. Mighell Fishery Biologists (Research), 

 Bureau of Commercial Fisheries Biological Laboratory Seattle, Wash. 98115 



ABSTRACT 



Tagging experiments show that Rocky Reach Dam, 

 constructed on the Columbia River 7 miles above 

 Wenatchee, Wash., in 1957-61, has not appreciably 

 increased the time required for adult sockeye salmon 

 (Oncer hynchns nerka) to migrate to Zosel Dam on 

 the Okanogan River (a tributary to the Columbia River 

 above Rocky Reach Dam). Water temperature of the 

 Okanogan River is, however, a major cause of delay. 



.\bove 70° F., rising or stable Okanogan River tempera- 

 tures block the entry of the fish from the Columbia 

 River into the Okanogan River; falling temperatures 

 allow the migration to resume. Below 70° F., migra- 

 tion is not blocked by rising or stable temperatures. 

 Delay may reduce survival because it increases the 

 exposure of the sockeye salmon to other factors that 

 affect them adversely. 



INTRODUCTION 



If Pacific salmon {Oncorhynchus spp.) and steel- 

 head trout (Salmo gairdneri) are to reproduce 

 successfully, sufficient adults in spawning condition 

 must reach the spawning grounds. Consequences 

 can be serious if the migrants are delayed en route. 

 Thompson (1945) showed, for example, that of the 

 tagged sockeye salmon (Oncorhynchus nerka) that 

 had been delayed longer than 12 days at the Hell's 

 Gate rock slide on the Fraser River, British Colum- 

 bia, in 1941, practically none reached their spawning 

 grounds. He also suggested that lesser delays re- 

 duced the reproductive capacit.y of the fish. 



Although thej' are equipped with facilities for 

 passing fish, hydroelectric dams on the migration 

 loutes constitute another type of barrier which can 

 delay adults en route to their upstream spawning 

 grounds. To assess and find ways to minimize the 

 effects of the.se dams as they are built on the Colum- 

 bia River is a most important aim of the agencies 

 concerned with the salmon and steelhead resources 

 of the stream. One facet of this work is to detect 



Note. — .Approved for publication .\pril 28, 1966. 



and minimize any delay of the adults as they migrate 

 upstream. The time required for adults to locate 

 and ascend fish ladders is sometimes reduced, for 

 example, by altering the spill pattern to improve 

 attraction to the ladders or even by modifying the 

 ladders themselves. 



In this paper we show that Rocky Reach Dam, 

 constructed on the Columbia River, 7 miles above 

 Wenatchee, Wash., in 1957-61, has not appreciably 

 increased the time required for sockeye salmon to 

 migrate from Rock Island Dam (below Rocky Reach 

 Dam) to Zosel Dam on the Okanogan River, a 

 tributary to the Columbia River above Rocky 

 Reach Dam (fig. 1). We also illustrate how the 

 temperature of the Okanogan River periodically 

 blocks the upstream migration of the sockeye 

 salmon at the confluence of the Okanogan and 

 Columbia Rivers. 



This studj' originated as part of a broad program 

 to assess the effects of Rocky Reach Dam on the fish 

 and wildlife resources of the upper Columbia River. 

 The program was developed by repi-esentatives of 

 interested State and Federal agencies and financed 

 by Public Utility District Number 1 of Chelan 



FISHERY bulletin: VOLUME 66, NO. 1 



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