THOMAS: EVALUATION OF RETURN OF CHINOOK SALMON 



marked. Rather, the numbers migrating down- 

 stream were determined and the returns were 

 compared with returns from marked hatchery fish 

 stocked in the creek. It is assumed that fish 

 migrating from the channel and Abernathy Creek 

 would have the same rates of survival. Table 1 

 summarizes the number, size, time of migration, 

 and mark of each of the fish sources involved in the 

 evaluation. 



Table L-Summary of the number, size, time of migration, and 

 mark of the various fish sources included in the evaluation. 



'Approximate size and time of migration based upon fyke net 

 sampling. 

 ^Oxytetracycline. 



Migrants from the Incubation Channel 



A total of 4,620,600 unmarked fry were released 

 from the channel during the 1964-65 season. This 

 number represents a 78.5% survival from the 

 5,888,100 eyed eggs planted. If the mortality of 

 green eggs is also considered, the survival to 

 migrant stage was 75.0%. A description of tech- 

 niques for planting eggs and counting fry was 

 given by Thomas and Shelton (1968). 



Migrants from Abernathy Creek 



Numbers of female chinook salmon which 

 spawned in Abernathy Creek during the 1964 

 spawning season were estimated at 576 from 

 spawning ground counts. On the basis of an 

 average of 5,000 eggs per female, an estimated 

 2,880,000 eggs were deposited in the creek. Fry 

 migrating downstream from this area were 

 sampled with a fyke net, a method demonstrated 

 to be reliable by Tait et al (1962). Recaptures from 

 known numbers of marked fish released upstream 

 indicated that the net sampled 13.3% of the 

 migrating fish; the calculated survival of migrants 

 from natural spawning was 16,700, or 0.58%. 

 Flooding and superimposition of eggs during 

 spawning are probably responsible for this low 

 survival. These fish were unmarked and returning 

 adults could not be distinguished from those which 

 originated in the incubation channel. 



Chinook salmon spawning area in Abernathy 

 Creek extends for about 1 mile below the hatchery 

 weir. Returns from natural spawners would not 

 necessarily enter the hatchery holding pond. 



Releases of Hatchery Fingerlings 



All fish released from the Salmon-Cultural 

 Laboratory hatchery were marked in some 

 manner for later identification. Initially, all fish 

 were marked in mid-April 1965 by feeding tet- 

 racycline after the technique developed by Weber 

 and Ridgway (1962). All fish in a 100-fish sample 

 examined in late April showed fluorescent bands 

 on their vertebrae. Fish released into Abernathy 

 Creek in May had two bands and those in August, 

 three bands. These second and third marks were 

 poor because the fish fed little, presumably 

 because of the high level of drugs in the diet. Total 

 hatchery fish released with only tetracycline 

 marking totaled 557,649. 



Two groups of fish used in a nutrition 

 experiment received double fin clips, in addition to 

 the tetracycline marks. These two groups served 

 as controls in that the returning adults would be 

 easily recognizable from the clipped fins, and a 

 check of their vertebrae would indicate the per- 

 sistence of the fluorescence. The fin-clipped 

 groups, which numbered 161,579, were released in 

 mid- August 1965. 



Treatment of Adult Fish 



All adult chinook salmon returning to the hold- 

 ing pond at the Salmon-Cultural Laboratory were 

 examined during 1966-68. All fish returning as 2- 

 yr-old jack salmon and as 3- and 4-yr-old adults 

 were examined. Past records of age classification 

 indicated that numbers of 5- and 6-yr-old adults in 

 the Abernathy Creek spawning run are insig- 

 nificant. Fish that returned to Abernathy Creek 

 but not to the hatchery holding pond were not 

 included in the evaluations. No attempt was made 

 to sample the sport or commercial fisheries or to 

 search the adjacent streams and hatcheries for 

 strays. The evaluation is based only upon returns 

 to the Salmon-Cultural Laboratory holding pond. 

 No correction was made for strays from other 

 hatcheries or streams that might enter the holding 

 pond and be counted as survivors from the channel 

 since their number would be insignificant 

 (Worlund et al. 1969). 



All adult fish were measured and the sex was 



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