Before differences in body weight oftheale- 

 vins among the three segments of the spawning 

 ground can be ascribed to differences in en- 

 vironnaental conditions, it is necessary to con- 

 sider the time of spawning; the alevins from the 

 upper segment nnay have been larger because 

 spawning was earlier. The average dates of 

 spawning and density of spawners in 1961 from 

 the three segments of the spawning ground 

 were not well documented, but detailed ob- 

 servations had been made on time and density 

 of spawning in 1963 (McNeil, 1966a). 



In August and September 1963, Sashin Creek 

 had 16,757 pink salmon spawners. We estimated 

 the average density of spawners to be about 

 0.9 female per square meter in the middle 

 segment and 0.6 in the upper and lower seg- 

 ments. Although the size of a female apparently 

 had not bearing on the selection of a spawning 

 area, the time of spawning did-- early females 

 tended to concentrate in the upper segment 

 and late females in the lower. The nonuniform 

 distribution of spawners supported the con- 

 tention that eggs were deposited earlier in the 

 upper segment than in the middle or lower 

 segment. The larger alevins in the upper 

 segment may, therefore, have resulted from an 

 earlier date of egg deposition rather than from 

 differences in growth due to differences in 

 environmental conditions. 



It seems unlikely that the larger alevins 

 in the upper segment could have been the 

 result of a genetically superior stock, because 

 the total available spawning area (13,629 n-i. ) 

 in the stream is confined to a channel only 1,000 

 m. long. Furthermore, the study segments are 

 continuous and no permanent tributary streams 

 enter Sashin Creek over the length of the study 

 area. 



1965 Brood Year 



We studied the distribution of spawners in 

 1965 the same way as in 1963 but sampled 

 eggs and alevins (the 1965 brood) more in- 

 tensively. The eggs and alevins were sampled 

 in three periods: late September, at the end of 



spawning; late November, during hatching; and 

 late March, before the fry emerged. The 

 escapement to Sashin Creek in 1965 ( 14,813 pink 

 salmon) included 7,109 females. The densities 

 of females were about 0.6 per square meter in 

 the upper and middle segments and 0.4 in the 

 lower. Average dates of spawning differed little 

 in the upper and middle segments (see table 10 

 of McNeil, 1968), butthe lower segment seemed 

 to attract mostly late spawners. 



Hence, in 1965 we had an excellent oppor- 

 tunity to connpare differences in growth and 

 developn-ient of embryos and alevins, especially 

 between the upper and middle segments, where 

 fish were at alnnost the same density and 

 spawned about the same time. About 75 percent 

 of live eggs and alevins in the streambed in 

 late September 1965 had died by late March 

 1966; the total number of live specimens in the 

 samples also decreased. 



The potential for differences in growth and 

 development in the three segments was en- 

 hanced by pronounced differences in water 

 quality brought about by a drought in 1965. Oxy- 

 gen values were high in August and low in 

 September (table 1); on September 22, after 

 most fish had completed spawning, the dis- 

 solved oxygen content of intragravel water was 

 low- -only 71 percent of saturation in the upper 

 segment, 40 percent in the nniddle, and 27 per- 

 cent in the lower. 



Because spawning was considerably later in 

 the lower segment than in the upper and middle 

 segments, comparisons of the size of body 

 parts and stages of development are restricted 

 to embryos and alevins from the upper and 

 middle segments. 



September samples .-- The September sam- 

 ples contained only embryos because develop- 

 ment had not proceeded to the alevin stage. 

 Embryos were examined for the presence of 

 pigmented eyes, diameter of eye, and length 

 of pectoral fin (table 2). The samples were 

 taken September 25-29; an equal number of 

 points were sampled in each area on each 



Table 2 Development and size of pink salmon embryos in 



upper and middle segments of Sashin Creek, September 25- 

 29, 1965 (Mean values and 90-percent confidence limits 

 are given) 



■'" Estimated from random subsample of 150. 



3 



