HEARD: PROBABLE CASE OF STREAMBED OVERSEEDING 



numbers of tagged females more accurately than 

 large numbers of untagged females. Because the 

 relative accuracy of the two methods is unknown, I 

 averaged them to arrive at mean estimates of den- 

 sities of females in the three areas (Table 2). 



Spawner density in Sashin Creek is usually un- 

 equal in the three study areas, depending in part 

 on the total number of spawners. Densities in 1967 

 were the highest recorded for specific areas-'^ of the 

 stream (Table 3). Merrell (1962) noted that in 

 years when many spawners were present, they 

 utilized all of the available spawning grounds, and 

 in years when few were present, they spawned 

 mostly in the lower portion of the stream. When 

 the upper area was used, survival of eggs and 

 alevins in that area was higher and the number of 

 fry produced was proportionally much greater 

 than in the middle and lower areas (Merrell 1962). 

 In addition, the sediment content and water qual- 

 ity of the stream in the upper area were better 

 than in the other two areas (McNeil 1966, 1968). 

 Sashin Creek thus presents an apparent 

 paradox — the least favorable areas are used in 

 years of relatively few spawners, and the best 

 areas are used only during years of great numbers 

 of spawners. 



Merrell ( 1962) thought that che greater use of 

 the upper area was related primarily to density- 

 dependent spawner interactions. In 1967, how- 

 ever, the heavy use of the upper area was appar- 

 ently not the result of high densities downstream 

 forcing spawners into upstream areas: spawner 



^Although the total number of spawners entering the stream 

 has been recorded since 1934 (Table 1), detailed studies on the 

 distribution of spawners in the upper, middle, and lower areas of 

 the stream have been available only since 1961. 



Table 2. — Estimated densities of female pink salmon spawning 

 in three areas of Sashin Creek, 1967. 



Females per square meter 



Area 



Based on counts of 

 tagged females only 



Based on counts of tagged 

 and untagged females 



Mean 



'Extrapolated from subjective estimate (McNeil et al. 1964). 

 ^Adjusted from McNeil (1966). 

 ^McNeil et al (1969). 

 "McNeil (1968). 

 ^Ellis (1969). 



densities in the upper area built up rapidly before 

 spawning reached significant levels in the middle 

 and lower areas. Although the upper area contains 

 only 22'7f of the combined spawning grounds of the 

 three areas, in 1967, 62^/ of the first group of 

 female pink salmon tagged at the weir spawned in 

 the upper area (Table 4). In general, the intensity 

 of spawning in 1967 progressed to downstream 

 areas from the upper area rather than the reverse. 

 McNeil (1966, 1968) noted similar downstream 

 shifts in spawning in Sashin Creek in 1963 and 

 1965. Although McNeil (1966) felt that the shift 

 occurred because of heavy rainfall during the 

 spawning period, he later noted ( McNeil 1968) the 

 same phenomenon during an unusually dry year. 

 It appears that the upper area in Sashin Creek is 

 not necessarily used because of spawner overflow 

 but because of more complex factors. Two interre- 

 lated factors could account for the spawner dis- 

 tributions observed in recent years: 1) migratory 

 behavior associated with timing of the escape- 

 ment, and 2) a genetic tendency for odd-year 

 spawners to use upstream areas. Odd-year spawn- 

 ers enter the stream earlier than even-year spawn- 

 ers. A characteristic of early stream entry in 

 anadromous fishes may be a tendency to migrate 

 farther upstream than spawners associated with 

 late stream entry (Briggs 1955). In addition to 

 early entry and use of the upper area, odd-year 

 spawners for the past 9 or 10 generations have 

 consistently had higher escapements and, except 

 for 1967, higher freshwater survival of progeny 

 than even-year spawners (Table 1). Natural selec- 

 tion may be operating, in recent odd-year genera- 

 tions, to encourage progeny produced in the upper 

 area to spawn in that area. Wells and McNeil 

 ( 1970) showed that fry produced in the upper area 

 of Sashin Creek were larger and presumably of 

 better quality than those produced in the 

 downstream areas. Differential marine survival 



Table 4. — Dates of tagging and percentage of total escapement 

 counted through weir, numbers of female pink salmon tagged, 

 and spawning distribution of tagged females in three areas of 

 Sashin Creek, 1967. 



Percentage of 

 total escape 



Tagged 

 females 



Percentage of tagged 

 fisti accounted for 



'Females tagged on each date received color-coded tags that differentiated 

 them from females tagged on other dates. 



571 



