DISAPPEARANCE OF DEAD PINK SALMON 



EGGS AND LARVAE FROM SASHIN CREEK, 



BARANOF ISLAND. ALASKA 



by 



William J. McNeil, Fishery Research Biologist, 



and Ralph A. Wells and David C, Brickell, Fishery Aids 



Bureau of Commercial Fisheries Biological Laboratory 



U.S. Fish and Wildlife Service 



Auke Bay, Alaska 



ABSTRACT 



The abundance of dead 1961 brood year pink salmon eggs and larvae was ob- 

 served from October 1961 to March 1963 in a small Southeastern Alaska stream, 

 Sashln Creek. Dead eggs disappeared slowly from the spawningbeds between the 

 end of spawning (October 1961) and the beginning of fry emergence (March 1962). 

 Significant numbers of fragments from dead 1961 brood year pink salmon eggs 

 were found in spawningbeds as late as March 1963. Dead 1961 brood year larvae 

 decomposed more rapidly than eggs, disappearing from spawningbeds before 

 August 1962. 



Dissolved oxygen levels averaging near 50 percent of saturation were observed 

 in Sashln Creek spawningbeds when decomposing eggs were present. The evidence 

 did not contradict the hypothesis that decomposing eggs may impair water quality 

 for more than 1 year beyond the date of spawning. 



INTRODUCTION 



Research to gain a better understanding of 

 factors limiting production of pink salmon 

 (Oncorhjnchus gorbuscha) in fresh water has 

 been conducted by the Bureau of Commercial 

 Fisheries since 1934 in Sashln Creek near 

 the southern end of Baranof Island, South- 

 eastern Alaska. Spawning escapements of 

 nearly 50,000 females with a potential deposi- 

 tion of about 100 million eggs have been ob- 

 served on the 13,600 square meters of Sashln 

 Creek spawning ground. 



Production of pink salmon fry from selected 

 segments of the Sashin Creek spawning ground 

 was first evaluated in early 1960 (1959 brood 

 year). The results suggest that steep-gradient 

 segments of the spawning ground possess a 

 greater potential to produce fry than shallow- 

 gradient segments (Merrell, 1962). 



Research on the fry production potential 

 of spawning beds was expanded more recently 

 at Sashin Creek to examine critically the 

 relation between quality of the spawningbeds 

 and the growth, development, and survival 

 of young salmon prior to fry emergence. As a 

 part of this research, mortality of eggs and 

 larvae is estimated periodically in Sashin 

 Creek spawningbeds. The measurement of 

 mortality is made difficult in certain instances 

 by the disappearance of eggs and larvae from 

 spawningbeds because of factors such as 

 gravel movements, decomposition, scavenging 

 and predatlon. As pointed out by Kaganovskii 

 (1949), McDonald (1960), and McNeil (1962a), 

 these factors introduce bias to total mortality 

 percentages calculated from live-dead 

 ratios. 



The processes of decomposition are sig- 

 nificant because decomposing organic matter 



