Appendix tables 1-5 give the number of 

 each age group by weekly periods from 1949 to 

 1953. Sometimes hatchery releases contribute 

 fish that confuse the picture. In 1951 a release 

 of marked I's from Winthrop station appeared 

 in weeks 17 and 18 at Bonneville. Normally, I's 

 would not be expected in the catch that early in 

 the year. In 1953, two I's that were probably 

 from a Little White station release were caught 

 in weeks 21 and 22. This catch, again, was 

 earlier than this age group usually appears. 



Lengths of Migrants 



The lengths of blueback migrants, even 

 within age groups, showed wide variation, par- 

 tially caused by the growth added during the . 

 summer. Another possible cause of variation 

 in lengths of bluebacks caught at Bonneville is 

 that the population is a mixture of fish from 

 Lakes Osoyoos and Wenatchee, and to some ex- 

 tent from other lakes in the Columbia River 

 system. The Leavenworth and Winthrop hatch- 

 eries, which obtain their eggs from the Lake 

 Wenatchee stock, produce most of the artificial- 

 ly reared bluebacks released into the Columbia 

 River system. These hatcheries formerly re- 

 leased blueback fingerlings into Lakes Osoyoos 

 and Wenatchee, and to some extent into the 

 Wenatchee, Entiat, and Methow Rivers, but in 

 recent years most of the hatchery production 

 has been released into Lake Wenatchee and its 

 tributaries. Some of the downstream -migrant 

 bluebacks might be icokanees (land-locked blue- 

 backs) from any of several lakes in the Colum- 

 bia system. Both live and dead kokanees have 

 been found below Grand Coulee Dam, and some 

 of the survivors on their way to the ocean prob- 

 ably would be caught at Bonneville. All of these 

 variables could affect the length data from the 

 Bonneville fingerling-trap catches. 



Gangmartc and Fulton (1952) state that 

 there is quantitatively more plankton in Lake 

 Osoyoos than in Lake Wenatchee, and that the 

 kokanees in Osoyoos are larger. A logical 

 assumption would be that bluebacks in Osoyoos 

 also are larger. No separation of these popula- 

 tions by length -frequency graphs is consistently 

 apparent, as shown by figures 11 and 12 and 

 figures 13-17. The average sizes of the2's are 

 slightly bimodal before week 2 j . Perhaps the 



separation of the different races is obscured by 

 one of the races being more abundant. 



The 1 ' s have ranged from 39 to 116 mm . , 

 with the largest before week 25 being 84 mm . 

 (week 24 in 1952). Those over 90 mm. do not 

 appear until later m the year. The I's ranging 

 from 39 to 50 mm . caught in 1949 are believed 

 to be part of a Little White hatchery release. 

 Another Little White release probably contrib- 

 uted the two fish, of 52 and 58 mm . caught in 

 weeks 21 and 22 in 1953. Three marked I's 

 from a Winthrop hatchery release were caught 

 in weeks 17 and 18 in 1951 and measured from 

 62 to 71 mm . The I's released by Little White 

 hatchery appear to be smaller than the average 

 of the bypass catches, while those released by 

 the Leavenworth and Winthrop stations are 

 larger than the average migrant at the time of 

 release. 



The lengths of the 2's ranged from 64 

 to 247 mm. The small 2's from 64 6o 80 mm. 

 usually migrate in the spring, and have never 

 been confused with the I's. The peak migration 

 period consists principally of 2's from 80 to 

 120 mm. Fish and Hanavan (1948) stated that 

 the blueback migrants from Lakes Osoyoos and 

 Wenatchee were all yearlings that ranged from 

 3 . 5 to 5 inches, or 89-127 mm . Most of the 

 spring -migrant 2's in the present study were in 

 this range. Few spring-migrant 2's were over 

 170 mm. By October, all 2's were over 150mm. 

 There were no I's in the fall and winter catch 

 of any year that could be compared with the large 

 2's from 130 to 194 mm. caught the following 

 spring. A spring release of marked 2's from 

 Winthrop ranged in length from 138 to 194 mm. 

 in the Bonneville catch data. If these lengths 

 are consistent for other spring releases, these 

 large 2's may be hatchery fish, but more data 

 are necessary to prove or disprove this possib- 

 ility. One 112 -mm. marked blueback from a 

 fall release was measured (in week 19 in 1953); 

 a second specimen from the same release was 

 caught, but it was not measured. Hatchery 

 releases are discussed on page 26. 



All 3's were over 160 mm by week 25, 

 with the exception of one fish that was 148 mm. 

 The largest 3 caught before week 25 was 301 

 mm., and the largest after was 292 mm. The 4's 



18 



