Table 9. — Estimated percentage of eggs and alevins from the 1963 brood year of pink salmon that 

 disappeared from three areas in Sashin Creek during and after spawning 



upper area between mid-December and late 

 March. (Late March was a good time to esti- 

 mate survival because large numbers of fry- 

 emerged in early April.) 



The disappearance of dead eggs and alevins 

 from the spawning bed was also studied to 

 help identify possible causes of mortality. 

 The percentage of dead eggs and alevins 

 that disappeared was estimated by: 



Live + dead eggs and alevins in spawning bed 

 Potential egg deposition 



The percentage of eggs that disappeared 

 during the spawning period was about 3 times 

 greater in the nniddle and lower areas than 

 in the upper (table 9). Most of this loss was 

 from eggs discharged during spawning; post 

 mortem examination of 435 females showed 

 that only about 4 percent of their potential 

 egg deposition was retained in the body cavity, 

 anci loss of unspawned females to predators 

 was minor. Brown bears occur on the Sashin 

 Creek watershed, but we found no evidence 

 that they frequented the lower section of 

 stream before October--after pink salmon 

 had spawned. 



Disappearance of large numbers of eggs 

 during spawning occurs connmonly with pink 

 salmon. Superimposition of redds, which re- 

 sults in the dislodgment of eggs previously 

 deposited, is one factor that causes eggs 

 to disappear during spawning (McNeil, 1964a). 

 Coarse bottom materials may reduce the 

 magnitude of mortality from superimposition 

 of redds because the females cannot dis- 

 lodge large cobbles while digging, and the 

 eggs nnerely drift into the large interstices. 

 This may be a reason for the decreased 

 loss of eggs in the upper area during 

 spawning. 



Although evidence failed to indicate that 

 eggs and alevins disappeared fron-i the middle 

 and lower areas between the end of spawning 

 and the beginning of fry emergence, the 

 percentage that had disappeared fronn the 

 upper area increased from ZZ to 60 during 

 that period (table 9). An estimated 58 per- 

 cent had disappeared from the upper area 

 in autunnn before the nnid-December sam- 

 pling; this figure was very close to the esti- 

 mated 60 percent that had disappeared by 

 late March. 



The specific factors that caused eggs and 

 alevins to disappear from the upper area in 

 autumn have not been identified, but predators 

 or scavengers may have been innportant. 

 McDonald (1960) and McLarney (1964) found 

 that scavengers and predators feed more 

 heavily on salnnon eggs where bottom mate- 

 rials are coarse than where they are fine. 

 If scavengers or predators ate eggs and 

 alevins in the upper area, their rate of 

 feeding would probably be high in autumn 

 when water temperatures are relatively warm 

 (2° to 7° C.) and low in winter when they 

 are relatively cool (0° to 2° C.) 



I do not believe that disturbance of bed 

 materials from flooding caused eggs and 

 alevins to disappear from spawning beds, 

 because the flow of Sashin Creek is well 

 regulated. A regulated flow is provided 

 by lakes on the watershed which provide 

 temporary storage for water during periods 

 of high runoff. The maximum discharge over 

 a 12-year period (1952-64) was estimated 

 to be 21 m.3 (1 nn.3 = 35.314 cu. ft.) per 

 second. Maximum discharge affecting the 1963 

 brood year was estimated to be 15 m.3/sec., 

 and there was no evidence of dislodgnnent of 

 materials in the spawning bed or of debris 

 in the high-flow channel. 



