FISHERY BULLETIN; VOL. 76, NO. 3 



that favored fry produced in the upper area over 

 those produced in the downstream areas could ac- 

 count for the greater escapements of odd-year 

 spawners in recent years. 



SURVIVAL OF EGGS AND ALEVINS 



Survival of eggs and alevins from the 1967 brood 

 year was estimated in Sashin Creek for four time 

 periods: 1) from stream entry to end of spawning, 

 2) from end of spawning to hatching, 3) from 

 hatching to shortly before fry emergence, and 4) 

 from shortly before emergence to emergence and 

 downstream migration of fry. 



The estimates of survival were based on esti- 

 mates of the potential egg deposition of female 

 spawners and estimates of the surviving eggs and 

 alevins in the three study areas. Potential egg 

 deposition was estimated by multiplying the 

 number of females by average fecundity. Densities 

 of eggs and alevins were determined after spawn- 

 ing, during hatching, and before fry emergence by 

 sampling randomly selected 0.1-m- points in the 

 streambed with a hydraulic sampling technique 

 described by McNeil (1964a). The number of fry 

 migrating from the stream were estimated on the 

 basis of daily counts of fry migrating through a 

 weir at the stream mouth. 



Numbers of females entering the stream and 

 average fecundity were derived from counts and 

 samples taken at the weir. Of the 38,067 pink 

 salmon spawners entering Sashin Creek in 1967, 

 19,639 (52'7f ) were females. Total counts of mature 

 eggs from each of 35 females selected at random 

 from the run ranged from 810 to 2,954 (average 

 2,260) eggs/female (907r confidence limit of mean 

 fecundity was ±115 eggs). 



The percentage of eggs available for deposition 

 that are actually buried in the streambed is partly 

 dependent on the density of spawners. McNeil 

 ( 1964b) discussed the role of redd superimposition 

 and showed that at spawner densities approaching 

 3 to 4 females/ m^ of spawning ground, an upper 

 asymptotic limit on the density of eggs in the 

 streambed is reached. Factors other than spawner 

 density that may influence egg deposition include 

 loss of adults in the stream before spawning and 

 retention of eggs in the female's body (Neave 

 1953), type and characteristics of the spawning 

 substrate (McNeil 1966), streamflow during 

 spawning (Ellis 1969), and loss of eggs to verte- 

 brate predators during the spawning process 

 (Moyle 1966; McLarney 1967; Reed 1967). 



The efficiency of egg deposition of pink salmon 

 spawners in Sashin Creek is highly variable, from 

 37 to 829^^ of the potential egg deposition (Ellis 

 1969). In 1967 the number of pink salmon eggs 

 potentially available for deposition was 44.4 mil- 

 lion, with 19.9 million of these (459^ of the poten- 

 tial) estimated to be in the streambed after spawn- 

 ing. The efficiency of egg deposition was 47'7f in the 

 upper area, 50% in the middle area, and 387f in the 

 lower area. 



Although spawner densities were high in 1967 

 (Table 3), the ability of pink salmon to void most of 

 their eggs during spawning did not seem to be 

 affected. Egg retention is characteristically low in 

 Sashin Creek, usually less than 57c of fecundity 

 ( McNeil 1966; Ellis 1969). In 1967, 1 examined the 

 body cavities of 402 spent female pink salmon 

 (about 2'7c of the total) and found that average egg 

 retention was 1.59^ of average fecundity. 



The proportion of eggs actually deposited that 

 were alive at the end of the spawning period in 

 1967 was highest (93%) in the upper area, inter- 

 mediate (83%) in the middle area, and lowest 

 (74% ) in the lower area (Table 5). This high survi- 

 val in the upper area is consistent with that of 

 previous years. The ratio of live to combined live 

 and dead eggs and alevins was usually higher in 

 the upper and middle areas than in the lower area 

 through hatching to the beginning of fry 

 emergence (Table 5). 



Survival of eggs and alevins varied among the 

 three time periods (during spawning, between end 

 of spawning and hatching, and between end of 

 hatching and emergence). Survival within each 

 time period for each area was higher between 

 spawning and hatching than during spawning or 

 between hatching and emergence (Table 6). As 

 previously discussed, survival during spawning 

 was related primarily to the ability of females to 

 successfully deposit their eggs because a high per- 

 centage of the eggs buried were alive shortly after 

 spawning. Survival between spawning and hatch- 

 ing and between hatching and emergence pertains 

 to survival of eggs and alevins within the 

 streambed. 



The densities of live preemerged fry in the 

 streambed of Sashin Creek in late March 1968 

 were 382, 260, and 108/m- in the upper, middle, 

 and lower areas, respectively. From these den- 

 sities I estimated a population of 2.9 million fry in 

 the entire stream. Operation of the fry weir began 

 just after the late March streambed sampling was 



572 



