The above rule applied to spring and 

 summer fishing. No zero catches were estimated 

 in the fall since chinook fishing usually comes 

 to a standstill for the year as soon as the catches 

 drop off to the point where fishermen can do 

 better using smaller meshed nets for silvers 

 (O . kisutch) , and chinook catches thus become 

 incidental. 



Calculation of Indices 



Assuming a consistency of effort for in- 

 dividual fishermen during similar periods of 

 successive years, and applying the criteria for 

 zero catches, a series of ratios (season n/, 

 season n-1) was established for the 27 years, 

 table 1. These ratios were obtained by compar- 

 ing the catch of the selected group of fishermen 

 for the spring, summer, or fall of one year 

 with the spring, summer, or fall catch one year 

 earlier or later. The catch -per- fisherman 

 week in pounds was calculated for one year, 1940, 

 which was established as the base upon which 

 catches -per -unit were calculated for other years. 

 Resulting catch -per -unit-of- effort index values 

 are shown in table 2 and the same information is 

 plotted in figure 2. 



CALCULATION OF EFFORT EXPENDED 



Dividing the total Columbia River catch 

 (table 3) by this catch -per -unit average gives the 

 number of gill -net -fishermen weeks employed 

 in making the catch. The result is a purely 

 hypothetical statistic because, for one reason, 

 there are other means employed than gill net 

 fishing in the Columbia River. The fishermen- 

 week calculation is merely used as a convenient 

 measure of total fishing effort based on gill net 

 activity alone . 



The resulting calculated values of total 

 gill -net catch -per-fishermen -week employed 

 are shown in table 4 and expressed graphically 

 in figure 3. The trend is a general decline in 

 effort with the most striking example occurring 

 in spring and summer. The fall fishing effort 

 has been more stable with an indication of de- 

 cline in the last three years 1952, 1953, and 

 1954. 



In search of reasons for a decline in ef- 

 fort expended in the Columbia River, some 



theorizing is done here. There have been some 

 changes in techniques which undoubtedly have in- 

 fluenced the efficiency of gill -net fishermen to a 

 degree. Removal of competing gear (seines and 

 fixed appliances) and use of faster boats, mech- 

 anized rollers, and a reduction from two-man to 

 one-man operated boats, are some changes which 

 have occurred in the last quarter. century. An- 

 other factor which has influenced the number of 

 gill -net fishermen -weeks employed in the chinook 

 fishery is the shortening of open seasons. Change 

 of fishing effort expended occurred during de- 

 pression years when prices paid to fishermen 

 were reduced in the panic of 1932. Strikes also 

 reduce the amount of effort. This can be verified 

 in several instances --the most recent example 

 occurring in August of 1952. Less profitable 

 fishing caused by declining runs in June and July 

 have obviously reduced the effort expended in 

 the summer. A high fishing effort occurred in 

 1940 as a result of unusual conditions experienced 

 by gill netters. Quoting from Pacific Fisherman 

 Yearbook (1941) the following statement is made: 



"May was described as one of the poorest 

 months in the history of the fishery. The usual 

 freshet was absent and exceptionally low water 

 prevailed most of the season which was especially 

 unfavorable for gill netters. Late June and July 

 brought some improvement but production con- 

 tinued below normal; and a peculiar fungus growth 

 on the nets, which is under investigation, caused 

 great difficulty in fishing." The fishing effort 

 measured by gill net catch -per -unit -of -effort 

 was undoubtedly distorted by the success of other 

 gear during that spring and summer. 



ESTIMATION OF ABUNDANCE 



From the data of gill -net -fisherman -weeks 

 employed, an estimate of total return can be made. 

 The formula first used by Baranov (1918), later 

 described by Ricker (1944), and used by Silliman 

 (1950), for the calculation of abundance, is as 

 follows: f2 = P2 in which "p" equals the in- 



stantaneous exploitation rate and "f" equals the 

 amount of effort expended. 



To use this formula certain requirements 

 must be met: (1) no significant natural mortality 

 must occur during the fishing season, (2) the 

 gear should be uniformly efficient, (3) the amount 



