niilus in nuclear growth and therefore in dis- 

 tinguishing fall and spring chinooks was de- 

 veloped, independent of fresh-water growth 

 itself. 



MATERIALS AND METHODS 



Materials for the present study were supplied 

 by the Fish Commission of Oregon and by the 

 Portland Program Office of the Bureau of Com- 

 mercial Fisheries of the U.S. Fish and Wildlife 

 Sei'vice. Scale impressions on cellulose acetate 

 cards of the following were available for study. 



1. Returns of marked fall chinook to Spring 

 Creek Hatchery: 



a. 1958 returns — released as fry, 1 fish ; 

 released as fingerlings, 8 fish. 



b. 1959 returns— released as fry, 8 fish; 

 released as fingerlings, 173 fish. 



c. 1960 returns — released as fry, 28 fish; 

 released as fingerlings, 158 fish. 



2. Returns of unmarked fall chinook to 

 Spring Creek Hatchery: 



a. 1959 returns— 925 fish. 



b. 1960 returns— 898 fish. 



3. Returns of marked fall chinook to Little 

 White Salmon Hatchery: 



Mark* 



Date released 



Fish returns 



Fish returns 



Xo. Xo, Xo. Xo. Xo. Xo. 



*L=left; P=pectoral; R — right; D = dorsal; 

 An=anal. 



4. Returns of unmarked spring chinook to 

 Carson National Fish Hatchery: Samples of 

 several hundred scales (one from each fish) 

 each year collected during 1955—57 and 1959-60. 



In addition to the above impressions of scales 

 of adult chinooks, specimens of young fall 

 chinook, preserved at the time of release at 

 several Federal hatcheries, were also available. 

 Scales from these young fish were studied for 



comparison with the nuclear zone of adult 

 scales. 



The study was based on objective means as 

 much as possible. Scales were studied under a 

 microprojector at magnifications of 92, 140, or 

 400 times, depending on the magnification de- 

 sired. The image of a scale was projected di- 

 rectly on millimeter graph paper, and the posi- 

 tions of circuli along the antero-lateral radius 

 of the scale were marked on the paper. The 

 center of the central plate was always used as 

 the starting point, and the edge of the central 

 plate became the first mark. In counting and 

 measuring the circuli, we regarded the mark 

 next to the central plate as the first circulus. 



All subsequent studies of the scale growth 

 were made from the markings on the graph 

 paper. Distances were measured in terms of 

 millimeters, and the actual dimensions deter- 

 mined by the magnifications used. The various 

 methods of counting, measuring, and graphing 

 will be described under individual sections. 



SCALE GROWTH IN FALL CHINOOK SALMON 

 RELEASED AS FRY AND FINGERLINGS 



Spring Creek Hatchery (fig. 1), a Federal 

 installation located about 175 miles from the 

 mouth of the Columbia River on the Washing- 

 ton side, produces primarily fall chinook sal- 

 mon. In the past, young chinooks were released 

 either as unfed fry during the first week of 

 February or as fed fingerlings during the first 

 week of May. To evaluate the relative merits 

 of fry and fingerling releases, the Bureau of 

 Commercial Fisheries marked young chinook 

 salmon of brood years 1956, 1957, and 1958. 

 Among the young released each year during 

 1957-59, some fish were marked, consisting of 

 about equal numbers of fry and fingerlings. 

 Two combinations of fin marks were used: 

 adipose and left pectoral fins on fry and adipose 

 and right pectoral on fingerlings. 



Fish with both marks were recovered in 

 years 1958-60,^ and scales were collected from 

 all returned fish. An interesting question here 

 is : "Can the scales of adults that were released 

 as fry be differentiated from those that were 

 released as fingerlings?" This problem is of 

 both theoretical and practical importance. 



Later recoveries are not included in the present study. 



SCALES OF CHINOOK SALMON 



167 



