Orsi and Jaenicke Marine distribution and origin of prerecruit Oncorhynchus tshawytscha 



485 



tend to bend or straighten when large fish strike 

 (Orsi, 1987). The data were also limited because we 

 did not retain CWT fish >66 cm FL, which are typi- 

 cally age -.3 fish (Wright et al., 1972). 



Scale and CWT ages, when available for the same 

 fish, were used to compare age-determination tech- 

 niques each season. Although freshwater and ma- 

 rine age can be misinterpreted from reported CWT 

 release information, we assumed that the release 

 year reported for CWT chinook salmon (Johnson and 

 Longwill') was also the year of seawater entry un- 

 less specified otherwise. We rejected age determina- 

 tions based on scale analysis for fish in time periods 

 or regions where they were unlikely to occur and were 

 not substantiated by CWT recoveries; examples of 

 this were age 0.0 fish in September in the northern 

 and central regions, age -.0 fish in February and May 

 and age 0.1 fish in February and May in the north- 

 ern region. 



We used X 2 tests to examine differences in the pro- 

 portion of male and female CWT chinook salmon by 

 ocean-age group for each period. In September, all 

 three ocean-age groups were present (i.e. age -.0, -.1, 

 and -.2), whereas in February and May, data were 

 available for only the age -. 1 and -.2 ocean-age groups. 



Length analysis 



Box-and-whisker plots (Tukey, 1977) were performed 

 for length ranges of each age group of chinook salmon 

 within each region and time stratum to ensure accu- 

 rate ageing and length representation. Values over 

 1.5 times the inner quartile range (IQR) were exam- 

 ined to identify extreme cases in length within a given 

 age group that may have resulted from errors (by 

 misinterpreting scale position on a scale card or by 

 transposing age values). After extreme values had 

 been examined and age or length reassigned as ap- 

 propriate, box-and-whisker plots were reconstructed 

 and values >3.0 times the IQR were eliminated from 

 the database unless substantiated by CWT fish. The 

 eliminated values constituted less than 0.5^ of the 

 data. 



To demonstrate temporal and regional differences 

 in length-frequency distributions of chinook salmon, 

 length data were plotted for the three sequential 

 sampling periods (September 1986, February 1987, 

 and May 1987) from fish in inside and outside wa- 

 ters (when possible) in the northern and southern 



7 Johnson, J. K., and J. R. Longwill. 1988. Pacific salmonid 

 coded wire tag releases through 1987. Regional Mark Process- 

 ing Center, Pacific Marine Fisheries Commission, Metro Cen- 

 ter, Suite 170, 2000 S.W. First Ave., Portland, OR 97201-5346, 

 228 p. 



regions. All age groups were pooled in each length- 

 frequency distribution. 



To demonstrate seasonal size structure, fork 

 lengths of ocean- and stream-type chinook salmon 

 were plotted by age group and period. Fork-length 

 data were pooled across regions, years, and waters. 



Stock composition 



Coded-wire tag recoveries from chinook salmon and 

 the expanded number offish represented by each tag 

 code were used to determine stock composition. Ex- 

 panded numbers represent the total number of fish 

 represented by a CWT, based on the proportion of 

 tagged fish in a release group. Origin of chinook 

 salmon stocks represented by CWT's were pooled into 

 three geographic groups: southeastern Alaska, Brit- 

 ish Columbia, and Washington or Oregon. Washing- 

 ton and Oregon stocks were combined because most 

 recoveries from these regions originated from the 

 Columbia River basin. 



Catch per unit of effort (CPUE ) was used with CWT 

 recoveries to determine the spatial and temporal dis- 

 tribution of stock groups. To determine CPUE, ex- 

 panded numbers for a particular age and stock group 

 of chinook salmon were divided by the number of 

 hours fished. This CPUE was computed separately 

 for inside and outside waters and pooled across re- 

 gions. For examining spatial distribution of indi- 

 vidual age groups of ocean- and stream-type fish in 

 inside and outside waters, CPUE was plotted against 

 age for each stock group. For examining seasonal 

 distribution, CPUE was plotted against ocean age 

 and season for each stock group. 



Migration and growth 



Net migration rates for each CWT chinook salmon 

 were calculated by dividing the hypothetical "straight 

 line" marine distance traveled between release and 

 recovery points by the number of days since release. 

 Because of limited information on precise freshwa- 

 ter release sites for many CWT fish, freshwater dis- 

 tance was not included in the determination of mi- 

 gration distance. Direction of travel of each fish from 

 its marine entrance point to its recovery locality was 

 recorded to the nearest 45° directional interval (e.g. 

 N=337.6°-22.5", NE = 22.6°-67.5°, etc.). 



Growth rates were compared between ocean- and 

 stream-type CWT chinook salmon recovered during 

 seven seasonal periods after release: age -.0 fish in 

 September; age -.1 fish in February, May, and Sep- 

 tember; and age -.2 fish in February, May, and Sep- 

 tember. Specific growth rates, G, were determined 

 for CWT chinook salmon by dividing the difference 



