of gear should not change within each season, 

 and (4) a uniform pattern of arrival and depar- 

 ture of fish over the period of successive years 

 is necessary. The second requirement regard- 

 ing uniformity of gear is generally true. The 

 net sizes and methods have remained relatively 

 uniform . In regard to changing amount of gear 

 within the season, some fishermen are exclusive- 

 ly fall fishermen, some fish in the spring only, 

 and some in the spring and summer. Division 

 of the gill-net years into three seasons mini- 

 mizes the possibility of abusing this rule. The 

 last rule concerning uniformity of arrival and 

 departure is considered here. The chinook sal- 

 mon migration is known to vary several days 

 from one year to the next. Fishermen usually 

 manage to have access to the peak of the spring 

 wave of chinooks entering the Columbia River 

 by fishing up or down the river on opening day . 



Use of the Baranov formula requires a 

 base year in which the absolute abundance of 

 the return is known. With the commercial 

 catch record and data on passage of fish at 

 Bonneville Dam available this requirement is 

 satisfied. Escapement to streams below Bonne- 

 ville Dam is the unknown quantity. For this 

 information biologists from the state fishery 

 agencies were consulted. The year of 1947 was 

 chosen for the base year because of better 

 knowledge of average -weight data in that year 

 than in others. In table 5 the best estimates of 

 escapements to the various streams below Bonne- 

 ville Dam are presented. These estimates are 

 obtained from hatchery records, spawning cen- 

 suses, and actual counts provided by the Oregon 

 Fish Commission and the Washington State De- 

 partment of Fisheries . They are known to 

 contain error, but are the best estimates avail- 

 able and, as indicated by Silliman (1950), even 

 large errors in such estimates would not inval- 

 idate the final conclusions. 



From the information provided in the 

 1947 season, the seasonal fishing mortality "m" 

 can be obtained. This is done by dividing the 

 total catch in pounds for spring, summer, and 

 fall by returns. Returns are determined by add- 

 ing catch below Bonneville Dam plus escapement 

 below Bonneville Dam plus Bonneville counts . 

 Fishing mortality rates of 34. 1 percent, 64.4 

 percent, and 77.6 percent for spring, summer, 

 and fall were thus derived. Then by use of the 

 formula 2 = P2, in which "f" represents effort 



Tf PI 

 and "p" represents fishing mortality, one unknown 



"p" value is solved for- -values of effort and the 

 other "p" value being known. The known "p" 

 value is derived from the fishing mortality "m" 

 by Ricker's instantaneous mortality tables. The 

 calculated "p" value is converted to fishing 

 mortality rate "m" by the same table. The value 

 of "m" is then applied to the Columbia River in- 

 side catches to determine the estimate of total 

 returns. In the above equation ^ ancl ^2 repre- 

 sent one year previous to fj and Pj._ Fishing 

 mortality and estimated returns based on catch- 

 per -unit -of -effort of Columbia River gill-netters 

 appear in tables 7, 8, and 9, and this information 

 is plotted in figure 4. 



INFLUENCE OF WATER -USE PROJECTS 

 ON CHINOOK SALMON IN THE COLUMBIA 

 RIVER 



During the period in which the returns 

 of chinook salmon are compared in this report, 

 a great number of tributary water-use works and 

 several main-stem multi-purpose dams have been 

 constructed. Hydroelectric, irrigation, and flood 

 control facilities in the tributaries have influenced 

 the migration and natural habitat of the chinook 

 salmon, but main-stem dams occupy more im- 

 portant migration routes and therefore are in a 

 position to affect large numbers of chinooks. 



A summary of the components of the re- 

 turns, divided into the three seasons --spring, 

 summer, and fall, is presented in table 6. The 

 returns are converted into pounds by using 

 Bryant's unpublished weight data. Commercial 

 catch statistics were provided by the Oregon 

 Fish Commission and the Washington State De- 

 partment of Fisheries. Bonneville counts were 

 provided by the Corps of Engineers. 



Dams may influence the migration and 

 natural habitat of the salmon by either blocking 

 migration when no fishways are provided or by 

 requiring the fish to ascend the facilities pro- 

 vided for them . Habitat is influenced by water 

 storage behind dams which convert stream spawn- 

 ing areas to slow -flowing bodies of water unsuit- 

 able for spawning. Juvenile downstream migrants 

 must make their way over spillways or through 

 penstocks without special protection at large 

 installations . 



11 



