had been released below Rock Island Dam on 

 August 2, 1953, peaked at the Rock Island counting 

 stations on August 4, 1953. In our anal3'sis, there- 

 fore, we treated this tagged lot as though it had been 

 released in the Rock Island foreba.v on August 4. 

 This adjustment made it possible to treat all tagged 

 lots in all years as if they had been released in a 

 common location — the forebay of Rock Island Dam. 



Water Temperatures Along the Migration Route 



Records of temperatures are frequently lacking 

 from the Okanogan River at Mouse and the Colum- 

 bia River at Brewster, near their confluence, but are 

 available instead from Oroville on the Okanogan 

 River and from Rock Island Dam and Bridgeport 

 on the Columbia River (fig. 4). Certain features 

 are clearly evident in figure 4. First, in July and 



75 



70 - r. 



G5 



60 



=- 55 



75 



70 



1951 





65 



60 



55 



1952 



963 



A\ .'h 



10 20 31 10 20 

 JULV AUGUST 



10 20 31 10 20 

 JULY AUGUST 



Figure 4. — Comparison of Columbia and Okanogan River 

 temperatures, 1945, 1951, 1952, and 1963. 



August the Okanogan River is considerably warmer 

 than the Columbia River. Second, in terms of 

 trends (rises and falls over a period of several days) 

 the readings at Oroville and Rock Island (or Bridge- 

 port) reflect the situation in the two streams near 



MIGRATION OF SOCKEYE SALMON 



their confluence. The absolute readings vary con- 

 siderably within a river, however, particularly in the 

 Okanogan River, where daily differences occasion- 

 ally reach 4 or 5° F. (neither station was regularly 

 the higher). Caution must be used, therefore, in 

 comparing the absolute readings from the Oroville 

 and Monse stations. 



The methods we describe are not rigorous, and 

 our data are not precise. Yet we believe them to 

 be adequate for the purposes of this report. 



TRAVEL TIME BETWEEN DAMS 



Travel time of sockeye salmon from Rock Island 

 Dam to Zosel Dam was estimated in 1953 and 1954 

 before Rocky Reach Dam was built and in 1962 and 

 1963 after construction. Travel time from Rock 

 Island Dam to Rocky Reach Dam was measured in 

 1962 and 1963, after Rocky Reach Dam was built. 



TRAVEL TIME BETWEEN ROCK ISLAND 

 AND ZOSEL DAMS 



In the examination of the basic tagging data for 

 this phase of the study (tables 3-4 and figs. 5-6), 



J** 



-A^ 



"iS^^^ 



a^ElW. 



tWjn. 



iO 10 20 



' AUGUST 



Figure 5. — Number of tagged sockej'e observed at Rock 

 Island and Zosel Dams after release below Rock Island 

 Dam in 195.3 and 1954. The dates of release are designated 

 by triangles below the base lines and the number of fish 

 released is given in parentheses. Daily average tempera- 

 ture of the Okanogan River is given in the center panel. 



attention should be given first to the years before 

 Rocky Reach Dam was constructed. In 1953 the 

 sockeye salmon that had been tagged below Rock 

 Island Dam on July 31, August 1, and August 2, 

 peaked at Rock Island Dam on August 2, 3, and 4 

 in that order, and at Zosel Dam 6, 9, and 9 days 

 later. The tagged fish that were released below 



137 



