Table 1. — Frequency and stalislics of Mai distance of circnli 

 of two groups of scales from salmon returning lu Spring 

 Creek Hatchery: A — adult chinooks that were marked and 

 released as fry; B — adult chinooks that were marked and 

 released as fingerlings 



That the variances of circulus spacing in both 

 the first 5 circuli and the first 10 circuli are 

 significantly greater for the fry-released group 

 than for the fingerling-released group is as we 

 expected, because the fry group grows the 

 first 5 to 10 circuli in the river or estuary, 

 where food and temperature conditions can be 

 highly variable, while the fingerling group 

 grows these same circuli in the hatchery, where 

 the conditions are fairly uniform. Both groups 

 form circuli 16 to 25 in the ocean, which ex- 

 plains why there is no significant difference be- 

 tween the two variances. Why the group re- 

 leased as fry grows more widely spaced circuli 

 than does the group released as fingerlings is 

 not understood. Perhaps it is due to the earlier 

 entry into the ocean by the fry. 



SCALE GROWTH IN MARKED AND 

 UNMARKED FALL CHINOOK SALMON 



During the 3 years 1957-59 when the Bureau 

 of Commercial Fisheries marked the fall 

 Chinook salmon at the Spring Creek Hatchery, 

 both marked and unmarked fish were released 

 simultaneously. When the fish returned, the 

 unmarked fish had a much greater rate of re- 

 turn than the marked fish. Also, at the same 

 age the unmarked chinook were consistently 

 larger than the marked. Examples are given 

 in figure 5 in which the modal length of female 

 unmarked fish is 2 inches, or 6 percent, larger 



ChNTI\)tTLRS 

 60 70 80 90 100 110 



MARKED 

 N»77. X-33 6 



UNMARICED 



N-401. X-3S 



23- 

 24 



43- 

 44 



45- 

 46 



Figure 5. — Size frequencies of female 4-year-old Spring 

 Creek Hatchery marked and unmarked chinooks that 

 were released as fingerlings (1956 brood) returned in 

 1960. 



than that of female marked fish, which had 

 their adipose and right pectoral removed. Male 

 chinook salmon exhibited similar differences. 



To see if the diffei-ence in size between re- 

 turns of marked and unmarked chinook is 

 manifested in scale growth, we studied the re- 

 turns of 4-year-old females in 1960. We first 

 compared scales from fish of modal length in 

 each group (33-34 inches in the marked group 

 and 35-36 inches in the unmarked group). 

 Then, we studied unmarked fish 33 to 34 inches 

 long. To do this objectively, we constructed 

 and compared mean scale graphs showing cir- 

 culus spacing and growth pattern. Of the 

 marked fish returns, only the group released as 

 fingerlings were studied for very few returns 



SCALES OF CHINOOK SALMON 



171 



