mated to have disappeared diiriiisi spawMiiiij in tlie 

 ui)per area, 42 percent in tlie middle area, and (>2 

 percent in the lower area. In 1965, at similar densi- 

 ties of spawners, nmch smaller i)ercenta<res of tlie 

 potential egg deposition disappeared during 

 spawning: 7 percent in the ujiper area, 5 percent in 

 the middle area, and 31 percent in the lower aiea. 

 The high j^ercentage of eggs deposited in 11)65 

 may have resulted from low streamflow in the 

 period of spawning. Except for a fresliet on 

 August 30, which j)roduced a discharge of 3 m.' per 

 second, streamflow remained relatively low (less 

 than 1 m.-' per second) throughout the period of 

 spawning. Streamflow did nt)t increase until Octo- 

 ber 3 (after spawning had ended) when a second 

 freshet i^roduced a flow of 7 m.' per second. 



Table 12. — Percentage of potential egg deposition of pink 

 salmon that disappeared from three areas in Sashin Creek 

 during autumn and winter, 1963 and 1965 brood years 



t Estimate pertains to the early two-tliirds portion of the period of spawn. 

 ing. other estimates for summer were at the end of spawning. 



A relatively high percentage of the potential egg 

 deposition (36 percent) disappeared from tlie 

 upper area of Sashin Creek after spawning in 

 autumn 1963, but few eggs and alevins disappeared 

 in winter (table 12). Because the pattern of disap- 

 pearance was dissimilar in the middle and lower 

 areas in 1963, 1 postulated that scavengers or pred- 

 ators may have concentrated in the coarse bottom 

 materials of the upper area to feed on eggs and 

 alevins (McNeil, 1966). As I will show shortly, 

 however, turbulent water during periods of high 

 discharge in autumn may also have contributed to 

 the disappearance of eggs from the upper area. 



The rate of consumj)tion of eggs and alevins by 

 scavengers and predators is not known, but many 

 species of invertebrates are known to inhabit 



spawning beds where they may feed on eggs and 

 alevins ( Brigg.s, 1953; Ahnell, 1961; McDonald, 

 1960). Other inve.stigators (McLarney, 1964, and 

 Phillips and Claire, 1966) have found that sculpins 

 {('off us spp.) are capable of i)enetrating into 

 streanibeds and will feed on eggs and alevins where 

 fine particles do not restrict their movements. The 

 population of sculpins in Sashin Creek has been 

 e.stimated to include 15,000 to 20,000 fish 5 cm. or 

 longer total length (McLarney, 1964). According 

 to McLarney ( personal communication) , this num- 

 ber of sculpins woidd be capable of consuming a 

 significant portion ( perhaps 25-50 percent) of tiie 

 total number of eggs estimated to have disappeared 

 in the autumn of 1963 (about 1 million) and the 

 autumn of 1965 (about 2 million). 



McLarney (personal communication) als<j found 

 that ina,ny eggs dejM)sited in coarse materials are 

 near the surface of the .streambed and are vulnera- 

 ble to i)redation and to removal from the bed by 

 water turbulence. He detected the jiresence of eggs 

 near the surface of the bed by artificially creating 

 water turbulence within a 0.2-m.'- circular screen 

 placed on the surface of the Ixul and collecting the 

 eggs tliat were released from the streambed. About 

 150 points were te-sted in this manner in each of the 

 three areas during spawning in 1965 (about 25 

 points per area on eiu-h of six dates) . The number 

 of eggs collected by McLarney per 0.2 in.- in tlie 

 upper area was 3 times the number in tlie middle 

 area and 14 times tlie number in the lower area. 

 Thus, eggs were most susceptible to predation and 

 to removal from the bed by turliuleiit water in the 

 relatively coarse. l)ed materials of the upper area 

 and least susceptible in the relatively fine ma- 

 terials of the lower area. This result helps to ex- 

 ])lain why no eggs disappeared from the lower area 

 in the autumns of 19(53 and 19()5 (table 12). 



Other studies have shown that the portion of 

 eggs and alevins that disappear from Sa.shin Creek 

 spawning beds varies from winter to winter. The 

 numl)er of eggs and alevins did not decrease dur- 

 ing the wintei-s 1961-62 and 1963-64 (McNeil et 

 al., 1964; McNeil, 1966); yet in the winter of 

 1965-66, an estimated 27 percent of potential egg 

 deposition disappeared from spawning beds of 

 Sashin Creek. Factoi-s causing the disapj)earance 

 of eggs and alevins in the winter of 1965-66 have 

 not been identified. 



584 



U.S. FISH AM) WILDLIFE SKKVICE 



