FISHERY BULLETIN: VOL. 69. NO. 3 



Table 2. — Percentage mortality from fertilization to 

 hatching of pink salmon in relation to initial incubation 

 at low temperatures (number of eggs in each lot in 

 parentheses). 



* See Figure 3 for temperature regime for each treatment. 



Range in lengths among alevins in the ambient 

 temperature lots was 20.9 to 22.9 mm, but range 

 in length in the 3.0° C lots was 15.1 to 22.3 mm 

 (Table 3). 



Because of the increased mortality and ab- 

 normal embryonic development of Grace Creek 

 pink salmon eggs at temperatures of 4.5° C and 



Table 3. — Ranges in lengths (millimeters) of alevins 

 from eggs treated at four temperatures (number of 

 alevins measured in parentheses). 



lower, we conclude that initial incubation tem- 

 perature for these eggs should be higher than 

 4.5° C. This is in agreement with the 4.4° to 

 5.9° C threshold for normal development of sock- 

 eye and Chinook salmon eggs found by Combs 

 (1965). 



DISCUSSION 



The proposed Grace Creek hydroelectric pow- 

 er plant focuses attention on a fishery problem 

 that may become increasingly imjiortant if more 

 hydroelectric plants are to be built on Alaska 



streams. Where water for power generation is 

 drawn only from the deeper and colder waters 

 of reservoirs, the resulting stream temperatures 

 would be lower than normal during the salmon 

 spawning season and initial incubation period 

 (Figure 1). 



At Grace Creek the expected changes in water 

 temperature could affect salmon in several ways. 

 Delay in ripening of gonads of the adults after 

 they enter the streams because of the lowered 

 temperatures (Reingold, 1968) might result in 

 late spawning. The low initial incubation tem- 

 peratures would further delay development of 

 embryos, but if normal cleavage were not dis- 

 rupted this delay could be offset by the higher 

 winter temperatures. The net effect on time 

 of emergence and seaward migration of the fry 

 is not known. The predicted initial incubation 

 temperature of 4.5° to 7.2° C (Figure 1) for 

 pink salmon eggs at Grace Creek includes the 

 temperature 4.5° C, at which we detected ab- 

 normal development and increased mortality of 

 the embryos. Measures should therefore be 

 adopted to prevent deleterious temperature 

 changes. Provision of an intake designed to 

 draw water of a desirable temperature on de- 

 mand is suggested as minimum action to protect 

 the salmon. 



ACKNOWLEDGMENTS 



Theodore R. Merrell, Jr., generously gave of 

 his time and thoughts in discussions of the 

 problem. Charles J. DiCostanzo critically re- 

 viewed the manuscript and made suggestions to 

 improve clarity of presentation. 



LITERATURE CITED 



Combs, B. D. 



1965. Effect of temperature on the development of 

 salmon eggs. Prog. Fish-Cult. 27: 134-137. 

 Combs, B. D., and R. E. Burrows. 



1957. Threshold temperatui-es for the normal de- 

 velopment of Chinook salmon eggs. Prog. Fish- 

 Cult. 19: 3-6. 

 Efimov, V. I. 



1962. Vyzhivaemost' gorbushi v period embrional'- 

 nogo razvitiya. (Survival rate of pink salmon 

 (Oncorhynchus gorbuscha) during embryonic de- 



592 



