Table 2. — Estimates of number of eggs deposited by spring 

 Chinook salmon in the Yakima River system, 1967-61 



Year, subarea, and stream 



Mean fork 

 Redds length of Mean fe- Eggs de- 

 counted female cundity posited 

 spawner 



sketch to describe the function of the canal-con- 

 duit system. The trapping system is shown 

 diagrammatically in figure 5. 



Procedures for studying seaward migration were 

 similar for all years. Trapping began about April 1 

 when young salmon were not yet abundant and 

 continued until they became scarce — sometime in 

 June. Fish were removed from the trap with dip 

 nets at 8 a.m., 12 noon, 4 p.m., and 12 midnight. 

 The trapping "day" used here extended from 8 

 a.m. of the calendar day indicated to 8 a.m. of 

 the following day. Fish other than salmon were 

 counted and released. Young salmon were trans- 



FiGURE 4. — Diagrammatic sketch of the system for 

 sampling the seaward migration at Prosser. Low dam 

 diverts water into the canal; screens divert fish into an 

 underground conduit that carries them to the traps 

 and eventually to the river. 



ferred into tubs for closer iiaspection before they 

 were counted and released. 



Once a week a sample of young chinook salmon 

 was anesthetized in a 1 : 20,000 solution of MS 222. 

 Fork length to the nearest millimeter was recorded 

 from each fish. Weight to the nearest gram was 

 recorded from a randomly selected subsample of 

 about 50 fish per week. Scales, selected from a 

 stratified subsample, were placed between paii's of 

 glass slides and later examined with a microscope 

 to determine the age of the fish. 



AGE AND SIZE OF SEAWARD MIGRANTS 



Scales from 1,458 young chinook salmon cap- 

 tured at Prosser from 1959-63 revealed that fish 

 were either in their first or second year of life. 

 Certain differences between the age groups are 

 noteworthy. First, the two age groups do not 

 appear at Prosser at the same time; fish that are 

 in their second year appear in early April, but 

 fish that are in their first year do not appear until 

 June. Second, when samples that contain fish of 

 both age groups are viewed in tubs, the first-year 

 fish (even the few that are as long as the fish in 

 their second year) are readily distinguishable by 

 their stouter bodies. 



We reasoned that the stouter, first-year migrants 

 were not spring chinook salmon but rather fall 

 chinook salmon — progeny of adult fall chinook 

 salmon that spawn near Granger, 40 km. upstream 

 from Prosser. If they were spring chinook salmon 

 migrating downstream from the upriver spawning 

 areas, they would have had to mov^e through the 

 midriver areas in the winter or spring. But this 

 movement did not take place. We sampled the 

 Yakima River system extensively with electro- 



352 



U.S. FISH AND WILDLIFE SERVICE 



