20 



oc. 



UJ 

 Q. 



% 

 tij 



(U 

 llJ 



< 

 IjJ 



II -YEAR AVERAGE 



OCT. I 



NOV. 19 JAN. 7 FEB.25 APR.I8 MAY 27 JULYS SEPT. 2 

 DATE AT BEGINNING OF WEEK 



Figure 4.— Comparison of 1961-62 mean weekly temperature with long-term average of 

 Sashin Creek over the period October 1 to September 30. 



charges of less than 20 c.f.s. occurred during 

 47 days in 1961-62, compared with the 11-year 

 average of 42 days. Discharges in excess 

 of 500 c.f.s. occurred on only one occasion 

 in 1961-62, compared with an 11 -year average 

 of 2,4 times. We conclude, therefore, that the 

 periods of low streamflow in 1961-62 were 

 near the long-term average, but extreme high 

 discharge occurred less frequently than in an 

 average year. 



Water Quality 



Concentrations of dissolved oxygen, free 

 carbon dioxide, and ammoniacal nitrogen in 

 intragravel water samples taken from the 

 same 24 randomly selected points were meas- 

 ured in late August 1962 (table 4). These data 

 are considered here since they describe water- 

 quality conditions known to be associated with 

 a population of almost 100 dead eggs per 

 square meter. 



EHssolved oxygen levels of intragravel water 

 in the Sashin Creek study area were less 



than those reported for three other Southeast- 

 em Alaska streams 4 out of 5 years (McNeil 

 1962a, 1962b). During August when water tem- 

 peratures were near 13 C., McNeil observed 

 mean dissolved oxygen levels ranging from 

 6 to 8 mg./l. in 1956, 1958, 1959, and 1960. 

 In August 1957, oxygen levels averaged only 

 3 to 4 mg./l., and a high early mortality of 

 pink salmon eggs occurred shortly after spawn- 

 ing. Moreover, Phillips and Campbell (1962) 

 found that embryos of coho salmon and steel- 

 head trout (Salmo gairdneri) in Oregon streams 

 suffered high mortality when oxygen levels in 

 the spawning bed averaged less than 8 mg./l. 

 These authors found that under field conditions 

 dissolved oxygen levels were directly related 

 to egg survival. 



A period of low rainfall was thought to be 

 an important factor contributing to the low 

 dissolved oxygen levels in the intragravel 

 waters studied by McNeil in August 1957. On 

 the other hand, there was no evidence that 

 hydrological conditions in Sashin Creek during 

 August 1962 were unusual or unfavorable. 

 Comparison of mean August water tempera- 



