the 1959 returns at Spring Creek Hatchery* and 

 Little White Salmon River gives some evidence 

 that at Spring Creek Hatchery the 1955 brood 

 as well as the 1956 brood actually had heavy 

 returns as 3-year-olds. In 1957, 2-year-old 

 returns at Spring Creek Hatchery were more 

 than twice as great as jack returns in any other 

 year (appendix table 6). If this had been pri- 

 marily the result of a dominant 1955 brood, a 

 more pronounced bimodal distribution, par- 

 ticularly for male returns, would have been 

 expected in 1959 since a large return of 4-year- 

 olds would have been expected. Further evi- 

 dence of earlier maturity is given by the 

 numbers of 3-year-old marked adult return 

 to Spring Creek Hatchery in 1959 — an un- 

 precedented return with respect to other 

 marked Chinook studies in Columbia River. 



Similarity in size distribution of returns to 

 these and other Columbia River hatcheries in 

 1959 gives some indication that maturation 

 rates may be dominated by oceanographic con- 

 ditions. Anomalies of fish behavior due to un- 

 common oceanographic changes from 1956 to 

 1958 along the coasts of Oregon, Washington, 

 and British Columbia have been very apparent 

 during this period. Increased jack returns were 

 observed in Puget Sound and British Columbia 

 streams. Tropical species were observed in 

 northern waters, and major changes in migra- 

 tion routes for temperate species were noted. 

 It is therefore likely that a recent change in 

 the maturation rate of Columbia River fall 

 Chinook was a result of rather rare ocean- 

 ographic conditions which were not observed 

 for any other period within the range of years 

 encompassed by the present study. 



The most significant effect which a change 

 in maturation rate for the 1955 and 1956 broods 

 would have on the return data would be an 

 unduly high return in 1958 accredited to the 

 1954 brood, since 3- and 4-year-old returns 

 in 1958 would constitute the major returns of 

 the 1955 and 1954 broods, respectively. The 

 returns in 1958 would also be unduly high 

 since 1 year of mortality would be eliminated 

 for the 3-year-olds. This factor would also 

 act to increase the returns in 1959 from the 



1956 brood (incorrectly accredited to the 1955 

 brood when a 4-year lag is used).^ Improper 

 designation of age at return of 1955 and 1956 

 brood years does not materially affect the 

 present analysis since a regression study re- 

 lating releases and returns 4 years later 

 included only brood years 1941-49 when facil- 

 ities at Spring Creek Hatchery were constant. 

 For the more recent years we will examine 

 only the level of return, for the number of 

 fingerlings and fry released during this period 

 of questionable age allocation was relatively 

 constant. 



Effects of local straying . — The problem of 

 local straying is particularly difficult at Spring 

 Creek Hatchery since eggs are taken at Big 

 White Salmon River as well as at Spring 

 Creek, and the fry and fingerlings are released 

 in the respective areas. For this reason 

 Spring Creek and Big White Salmon River are 

 treated as one unit. Additional variation or 

 error is introduced, however, since the number 

 of natural spawners which contribute to the 

 return in Big White Salmon River can only be 

 estimated roughly. Furthermore, in some 

 years even the number of hatchery spawned 

 fish from Big White Salmon River is not given 

 and must be estimated from the number of 

 eggs taken. Further variation is introduced by 

 production from natural spawning. Also, when 

 fingerlings are reared at Spring Creek Hatch- 

 ery and released in Big White Salmon River, 

 it is questionable whether a significant portion 

 returns to either stream. 



At Spring Creek Hatchery, returns as well 

 as releases have been accurately recorded, 

 and for most of the analyses Spring Creek 

 Hatchery alone has been considered as a unit. 

 In order to determine the adaquacy of this 

 treatment, releases and returns at Spring 

 Creek Hatchery only have been compared with 

 combined releases and returns at Spring Creek 

 and Big White Salmon River. This comparison 

 is presented in a later section. 



* Floyd Anders. Bureau of Commercial Fisheries, 

 unpublished data. 



^ If the 1957 brood was unaffected by these changes, 

 a greatly reduced return in 1960 could result despite 

 a good production for the 1956 and 1957 broods, because 

 the major returns for 1956 may have returned in 1959 

 as 3-year -olds and the 1957 brood may produce pri- 

 marily 4-year-olds returning in 1961. 



