HEARD: PROBABLE CASE OF STREAMBED OVERSEEDING 



Table 7. — Percentage of potential egg deposition of 1967 brood 

 year pink salmon that disappeared from three areas of Sashin 

 Creek and from the entire stream by 1 October 1967, 1 December 

 1967, and 25 March 1968. 



' Data weighted and adjusted to include spawning grounds not included in the 

 three study areas. 



T.\BLE 8. — Estimated densities of all eggs and alevins (live and 

 dead) in three areas of Sashin Creek on 1 December 1967 and 25 

 March 1968, and percentage that disappeared between the two 

 dates. 



Number of eggs and alevins 

 per square meter on 



Area 



1 Dec. 



25 Mar. 



Percentage that 



disappeared 

 between dates 



Upper 

 Middle 

 Lower 



1,714 



1,591 



989 



647 

 702 

 350 



62 

 56 

 65 



or alevins to disappear from streambed gravels 

 may or may not have been the initial cause of 

 death. 



It is unlikely that turbulent streamflow, 

 streambed shifting, or predation were the reasons 

 that 1967 brood year eggs or alevins disappeared 

 between early December and late March, 

 Streamflows were generally low, and although an 

 intermittent ice cover was present on Sashin 

 Creek during January, February, and March, 

 there was no indication of streambed shifting be- 

 cause of ice scouring. A series of short metal stakes 

 driven into the streambed throughout the stream 

 in November to mark coho salmon, O. kisutch, 

 redds was still in place in March, indicating that 

 no streambed shifting had occurred. 



Most fish in Sashin Creek that could eat pink 

 salmon eggs and alevins (juvenile coho salmon; 

 rainbow trout, Salmo gairdneri; Dolly Varden, 

 Salvelinus malma\ and coastrange sculpin, Cottus 

 aleuticus) are essentially dormant during the 

 winter when water temperatures are low. Chap- 

 man and Bjornn ( 1969) have shown that resident 

 stream salmonids may disappear into the sub- 

 strate when water temperatures fall below 4.4 °- 

 5.5 °C. I have observed similar behavior in Sashin 

 Creek. Stream temperatures in Sashin Creek 

 were below 4.4 °C from 13 December 196-7 to 20 

 April 1968. 



Water ouzels, Cinclus mexicanus, and mergan- 

 sers, Mergus merganser, are occasionally present 

 on Sashin Creek during the winter and could ac- 



count for the disappearance of some eggs and ale- 

 vins during open water periods. In considering the 

 magnitude of the disappearance of 1967 brood 

 year eggs and alevins in Sashin Creek between 

 December and March, it is unlikely that the 

 maximum possible loss to these sources is sig- 

 nificant. This conclusion is based on the small 

 numbers of mergansers and ouzels present, the 

 amount of time the stream was covered with ice, 

 and the large number of eggs or alevins that dis- 

 appeared. Between two and five mergansers were 

 noted in the vicinity periodically. When present, 

 these birds spent much of their time in the inter- 

 tidal portion of Sashin Creek or in the adjacent 

 estuary. Only four of the smaller and territorial 

 ouzels normally occur along the upper, middle, 

 and lower areas of Sashin Creek in winter, and 

 during periods of ice cover these birds go 

 elsewhere. Based on periodic observations and 

 temperature records, I estimate the stream was 

 covered with ice approximately half the 1967-68 

 winter. 



The estimated population of live and dead pink 

 salmon eggs and alevins in Sashin Creek was 18.3 

 million on 1 December 1967 and 7.2 million on 25 

 March 1968 (Table 9), making a loss of 11.1 mil- 

 lion eggs and alevins between the two dates. Be- 

 cause there is little evidence that the loss was 

 caused by external factors that physically re- 

 moved eggs or alevins from the streambed, the loss 

 was likely due to factors within the intragravel 

 environment. 



The disappearance of 11.1 million eggs and ale- 

 vins from the streambed between hatching and 

 emergence led me to examine the relation between 

 live eggs and alevins and dead eggs and alevins in 

 the streambed. The densities of dead eggs and 

 alevins in the upper, middle, and lower areas (Ta- 

 ble 10) indicated that the numbers of dead eggs 

 and alevins remained relatively stable between 

 the time periods. This does not necessarily indi- 

 cate that dead eggs in the streambed during one 

 sampling period were still there during a later 

 sampling period. Dead eggs can disappear at any 

 time for many reasons, but can persist in a 



T.ABLE 9. — Estimated population of live and dead pink salmon 

 eggs and alevins in Sashin Creek on 1 October 1967, 1 December 

 1967, and 25 March 1968, 



575 



