The severity of this downward trend is even 

 more apparent where the adjusted return per 

 thousand pounds of fish released (fry and 

 finger lings) is plotted by brood year and re- 

 turn year (fig, 7). The inclusionof fry releases 

 in this plot should favor the values for recent 

 years since the percentage of fry released 

 after 1950 was greatly reduced (fig. 8). The 

 relatively low values for 1941 and 1942 brood 

 years (fig. 7) are associated with releases 

 which were almost 100 percent fry, and the 

 average level for these 2 years is very close 

 to the value for 1948 when only fry were re- 

 leased. The deviations from the regression 

 line indicated that in the 1940's the return per 

 pound of fingerlings released was greater than 

 the return per pound of fry (fig. 4). Figure 7 

 shows, however, that compared with the years 

 1941, 1942, 1948, and 1949, when a very high 

 percent of fry were released, the return per 

 pound released has been much less since 1950 



with increasingly higher percentage of finger- 

 lings. It would appear then, that a pound of 

 fingerlings in recent years does not produce 

 the return comparable to that from a pound of 

 fry in the 1940's. If, however, the downward 

 trend in figure 7 is due to genetic or disease 

 factors which affect both fry and fingerling 

 releases, the survival rate of fry in recent 

 years could also be reduced. 



The regularity and extent of the downward 

 trend exhibited in figure 7 suggests the ex- 

 istence of a time-related factor that affects 

 the index of production used here without 

 necessarily affecting the actual production. 

 An examination of any such apparent factors 

 does not confirm this hypothesis. For example, 

 if unadjusted female returns are used, the 

 same trend as in figure 7 is observed except 

 for returns for 1952 when results of a strike 

 obviously require adjustment. 



5° 



Z a 



"Z 



O O 



O 



O O 



BROOD YEAR 1941 1943 1945 1947 1949 1951 1953 1955 



RETUBN YEAR 1945 1947 1949 1951 1953 1955 1957 1959 



Figure 7.--Return rate of females to Spring Creek 

 Hatchery. 



oj 



• POUNDS OF FRY 



O POUNDS OF FINGERLINGS 



IROOD YEAH 1941 



o o • 



• • • 



Figure 8.— Pounds of fingerlings and fry released at 

 Spring Creek Hatchery, 



Relatively large numbers of fish were re- 

 leased in Big White Salmon River in earlier 

 years, and it might be suspected that increased 

 local straying from Big White Salmon River 

 could have increased the return to Spring 

 Creek in the 1940's. By using combined re- 

 leases and adjusted returns to Spring Creek 

 and Big White Salmon River to remove this 

 effect, the same trend as figure 7 (using 

 Spring Creek Hatchery data only) is obtained. 

 If a relatively constant percent of wild fish 

 stray to Spring Creek Hatchery, a larger 

 escapement of wild stocks in earlier years 

 could increase returns, but appendix table 8 

 shows that escapement of wild stocks as 

 measured by Bonneville counts is of the same 

 magnitude for the brood years 1945, 1946, 

 1947, as for the brood years 1953, 1954, and 

 1955. 



Increased fishing intensity in the ocean 

 fisheries may have affected returns, as can 

 be noted from the declining total run in the 

 Columbia River (appendix table 8). For the 

 1945 and 1946 brood years, however, the total 

 run was only about twice the total run for 

 brood years since 1951, whereas the return 

 per pound of fish released (fig. 7) for 1945-46 

 oroods was more than five times as great as 

 foi brood years since 1951. In addition, the 

 downward trend in the run in the river in these 



12 



