Figure 3. — Locations of search stations on Columbia River near Bonneville Dam where floaters were observed in 1954 



and 1955. 



—7 km. below the dam; (7) Moffett Creek— 

 3 km. below the dam opposite the mouth of 

 Moffett Creek; and (8) The Dalles— 72 km. above 

 the dam, 0.8 km. downstream from The Dalles, 

 Oreg. 



At each station, an observer in a boat roved 

 back and forth across the river 8 hours a day on a 

 transect perpendicular to the riverflow. All ob- 

 servations were recorded in one of three cate- 

 gories: river site — midstream search at a station; 

 river vicinity — midstream search at other than 

 an established station (usually en route to and 

 from a station at the beginning and end of the 

 day); and shore — search on foot alongshore 

 (table 2). Eighty-two percent of the total search 

 time was at river sites, 15 percent at river vicini- 

 ties, and 3 percent on shore. Stations 6 and 7 

 were alternately manned by the same boat crew 

 at different times, depending on visibility. Ob- 

 servations began on April 4 at stations 2, 4, 6, 

 and 7 and on May 3 at station 8. The observer 

 at station 1 was moved to station 5 at the end of 

 June, and on July 12 the observer at station 4 

 was moved to station 3. A total of 1,666 hours 



and 50 minutes were spent on all searches in 

 1955 (table 2). 



By the time the observations began in April, 

 appreciable numbers of spring chinook salmon 

 had passed Bonneville Dam. The numbers passing 

 through the ladders increased rapidly in late April 

 and reached a peak on May 2, when 13,763 fish 

 were recorded. Only four chinook salmon floaters, 

 or 0.02 per hour of search, were found in April 

 at search stations, and only eight — again 0.02 per 

 hour — were found in May (table 3). Thus, in 

 April and May, when a record run of 170,205 

 spring chinook salmon passed the dam, the ob- 

 servers found only a few chinook salmon floaters 

 at the four stations between St. Helens and the 

 dam. 



During the first half of June, only 11,551 

 chinook salmon passed the dam, but 13 chinook 

 salmon floaters (0.07 per hour) were found down- 

 stream from the dam. In the second half of June, 

 most of the summer chinook salmon run (33, 951) 

 passed the dam, and searchers found an increas- 

 ing number as floaters below the dam — 0.23 per 

 hour of search (table 3). 



466 



U.S. FISH AND WILDLIFE SERVICE 



