minute. To simplify counting, the observers 

 were instructed to tally in groups of five 

 until the numbers passing decreased suffi- 

 ciently to permit individual tally of fish. 



Size and Species Considerations 



In a study of fishway capacity we must 

 necesscLrily give consideration to the size 

 and species composition of a fish population 

 which may be expected to pass a fishway 

 located in a given area of a river system. 

 For instance, if a fishway is limited 

 size, we may logically expect to pass great- 

 er numbers (per unit time) of a run in which 

 species average 5 pounds in weight than of 

 another run in which species average 10 

 pounds, other factors being equal. Further, 

 if the smaller of the two species is capable 

 of ascending the fishway twice as fast as the 

 larger, then the potential difference in 

 total numbers capable of passage per unit 

 time may become even greater when we compare 

 the capacity of the fishway with respect to 

 the two species. Conversely, the opposite 

 might be true if the larger of the two spe- 

 cies proves to be the better swimmer. Clearly 

 we must recognize . the possible effect of 

 these two factors — size and species perform- 

 tince — in our measure of fishway capacity. 



The three most common salmon passing 

 Bonneville Dam in order of abundance are (1) 

 Chinook ( Oncorhynchus tschawytscha Walbaum), 

 (2) blueback (0. nerka Walbaum), and (3) 

 silver (0. kisutch Walbaum). Two other spe- 

 cies, chum salmon (0. keta Walbaum) and pink 

 salmon (0. gorbuscha Walbaum) are also 

 known to pass the dam, the latter rarely. 



Except for chinook salmon, the steel- 

 head ( Salrao gairdneri Richardson) is usually 

 the most abundant salmonoid appearing at 

 Bonneville Dam. 



For comparative purposes, the average 

 weights of the various species will be used 

 as a measure of size. Weights of the above- 

 mentioned species, particularly chinook 

 salmon (Silliman e_t al. 1947) may vary con- 

 siderably between and within years. The fol- 

 lowing average weights (Cleaver 1951) are 

 presented to demonstrate characteristic size 

 differences among salmonoids present in the 

 Columbia River: chinook salmon, 17 — to 



FIGURE 8.--0PERATiONS RECORDER USED TO RECORD 

 FISH PASSAGE IN NUMBERS PER UNIT TIME. 

 EACH PASSAGE IS NOTED IN THE FORM OF A 

 BLIP ON THE RECORDER TAPE AT THE EXACT 

 MOMENT OF OCCURRENCE. 



20- pounds; steelhead, 9 pounds; blueback, 

 3 pounds; and silver salmon, 10 pounds. 



Average weights obtained during Septem- 

 ber 1949 (Schoning et al. 1951) at Celilo 

 Falls (now inundated), which was approxi- 

 mately 50 miles above Bonneville Dam on the 

 Columbia River, showed that chinook salmon 

 average 15.7 pounds; steelhead, 9.25 pounds; 

 and silver, 7.1 pounds. 



Average weights listed above apply to 

 fish taken in commercial catches and may 

 not, therefore, be directly applicable to 

 the salmonoid population passing Bonneville 



_4/ "Spring" run average. Arbitrarily 

 January 1 - July 31. 



5/ "Fall" run average. Arbitrarily 

 August 1 - December 31. 



