Table 12. — Estimates of the population parameters E', P, p'o, and M t used to evaluate mortality of 1960 brood year eggs and 



larvae possibly caused by movement of bed materials 



 Expected number of specimens based on potential egg deposition (£')• 



-' Estimated live plus dead specimens in the spawning bed (P). 

 ' These limits were set with log-transformed data. 



heavy precipitation in 1960; while in 1958 and 

 1959 the increase was about 0.10. The difference 

 between an increase of 0.16 and 0.10, however, 

 was not statistically significant in these instances. 

 As in 1958 and 1959, on occasions when there 

 was no movement of temporarily stationary 

 debris with high water, eggs and larvae in inter- 

 tidal Indian Creek apparently suffered little mor- 

 tality. There was also no evidence of mortality 

 associated with flooding in Twelvemile Creek in 

 1960, although large numbers of eggs had appar- 

 ently disappeared before high water. 



FREEZING OF INTRAGRAVEL WATER AND 

 MORTALITY 



The study streams freeze usually in December, 

 January, and February. Hence, mortality attrib- 

 utable to freezing must occur either during or 

 after hatching. 



Maximum daytime air temperatures were used 

 as as index of severity of freezing. Periods when 

 day time temperatures remained below freezing for 

 two or more consecutive days were determined 

 from air temperature records obtained at Hollis 

 by the Northern Forest Experiment Station 

 (table 13). Freezing was most severe in winters 

 1956-57 (1956 brood year) and 1958-59 (1958 

 brood year). 



1956 Brood Year 



There was evidence of high mortality from 

 freezing in whiter 1956-57. Estimates of M, for 

 the 1956 brood year in each of the study streams 

 are summarized in table 5. Mean values of M r 

 were found to increase between late November 

 1956 and late February 1957 as follows: 



A A 



M r =0.27 to M r =0.50 in intertidal Harris 

 River. 



A A 



.U r = 0.10 to M r =0.75 in intertidal Indian 

 Creek. 



A A 



M r =0.27 to M r =0.41 in intertidal Twelve- 

 mile Creek. 



Table 13. — Periods of daytime freezing and associated 

 precipitation at Hollis, Alaska 1956-61 ' 



i Data provided by Northern Forest Experiment Station, U.S. Forest 

 Service, Juneau, Alaska. 

 -' Fell as snow, given as inches of rain. 



SPAWNING BED ENVIRONMENT OF PINK AND CHUM SALMON 



517 



