Effects of fisheries. — Relative returns to 



Spring Creek Hatchery may be affected by 

 variations in the ocean troll fishery, sport 

 fishery, and the gill net fisheries in the 

 Columbia River below Bonneville Dam (zones 

 1-5) and above Bonneville Dam (zone 6). 

 Although the ocean fishery, particularly the 

 sport fishery, has increased very significantly 

 since 1950, it is not possible to correct for 

 this change since the contribution of Columbia 

 River stocks to this fishery is unknown. It is 

 also difficult to correct for the zone 6 gill net 

 fishery above Bonneville Dam since a large 

 and unknown portion of this fishery is above 

 Spring Creek Hatchery. In 1956, however, this 

 fishery was closed below Hood River Bridge, 

 and, in 1957, the area above Bonneville Dam 

 was closed. This closure had an impact on the 

 data, although no correction for it has been 

 made. 



The female returns to Spring Creek Hatchery 

 and Big White Salmon River have been adjusted 

 for the gill net fishery below Bonneville Dam, 

 which is the most important river fishery. By 

 treating the Bonneville count as the escape- 

 ment and the sum of Bonneville count and catch 

 below Bonneville as total run (ignoring lower 

 river escapement), the percent escapement has 

 been calculated for each year (appendix table 

 8). Dividing the number of females returning 

 to Spring Creek Hatchery by the percent 

 escapement gives an estimate of the number of 

 Spring Creek Hatchery females entering the 

 river. Multiplied by a constant value E, which 

 is the average percent escapement for the 

 years involved, these values are brought to the 

 same order of magnitude as actual returns 

 (appendix table 9, last three columns). These 

 values, which correct variations in the major 

 gill net fishery below Bonneville Dam, will be 

 referred to as "adjusted returns". Total female 

 returns to Spring Creek Hatchery or Big White 

 Salmon River have been adjusted in the same 

 way (appendix table 9). These data are given 

 for the brood years 1941-55 (1959 return). 



The effect of the adjustments may be seen 

 when adjusted and unadjusted female returns 

 to Spring Creek Hatchery are plotted for the 

 return years 1945 and 1959 (fig. 2). A strike 

 in 1952 increased the escapement considerably 

 so that the adjusted value in that year is greatly 



reduced. The effects of increased closures 

 which were initiated in 1956 are not readily 

 apparent until 1958. In 1959, as a result of a 

 poor run, the fishermen reduced their effort 

 in the first part of the season, and a slight 

 delay in the peak of the run permitted an un- 

 precedented percentage escapement during the 

 closed period. 



The Bonneville counts used to estimate per- 

 centage escapement include jacks, whereas 

 adjustments are on adult female returns. No 

 standard was used in the classification of 

 jacks passing Bonneville Dam; therefore, sub- 

 tracting jacks from the total count would 

 probably introduce more error than their in- 

 clusion. For example, in 1957, when the jack 

 return at Spring Creek Hatchery was 8,402 

 and the jack count over McNary Dam was 

 13,415, only 9,879 jacks were counted over 

 Bonneville Dam. 



Insofar as the gill net fishery is closed 

 during the peak of the Columbia River run of 

 fall Chinook, a concentration of the Spring 

 Creek run at this time could greatly reduce 

 their availability to the fishery. Such an oc- 

 currence would invalidate the adjustment made 

 in appendix table 8. Results of a tagging ex- 

 periment conducted by Oregon Fish Commis- 

 sion at Bonneville Dam in 1956 were studied 

 by the Bureau of Commercial Fisheries (U.S. 



° ° RETURN ADJUSTED TO CONSTANT FISHING EfFOBT 



• ACTUAL RETURN 



z < 



s o 



BROOD YEAR 1941 

 RETURN YEAR 1945 



1943 

 1947 



1945 

 1949 



1947 

 1951 



1949 

 1953 



1951 

 1955 



1953 

 1957 



1955 

 1959 



Figure 2.- -Comparison of adjusted and unadjusted 

 female returns to Spring Creek Hatchery as defined 

 in appendix table 9. 



