MIGRATION AND DISTRIBUTION OF PINK SALMON SPAWNERS IN SASHIN 

 CREEK IN 1965, AND SURVIVAL OF THEIR PROGENY 



By William J. McNeil, Head, Pacific Fisheries Laboratory, Oregon State University Marine Science 



Center, Newport, Oregon 97365 



ABSTRACT 



The escapement of 14,813 pink salmon (Oncorhynchus 

 gorbuscha) to Sashin Creek, southeastern Alaska, in 

 1955, followed by the emergence of 2.2 million fry, or 

 18 percent of the potential egg deposition, represented a 

 relatively high survival of eggs and alevins in a stream, 

 where the long-term average is 7 percent. This high 

 survival was predicted from an established relation be- 

 tween survival of eggs and alevins and the time the 

 parents entered Sashin Creek to spawn. 



The spawning ground was divided into three areas — 

 upper, middle, and lower — to study density of spawners 

 and survival of their progeny. Density in 1965 was higher 

 in the middle and upper areas than in the lower. From 

 egg deposition to fry emergence, survival was estimated 



to be 23 percent in the upper area, 18 percent in the 

 middle area, and 14 percent in the lower area. 



The instantaneous rate of mortality remained rela- 

 tively unchanged from deposition of eggs to emergence 

 of fry in the upper and middle areas. In the lower area, 

 mortality was relatively high during spawning and low 

 between spawning and hatching of eggs. Much of the 

 mortality throughout the stream was traced to the 

 disappearance of eggs and alevins. Factors causing this 

 disappearance included retention of eggs, super- 

 imposition of redds, predation, and turbulent water. 

 A drought during spawning retarded development of 

 embryos and caused considerable mortality. 



The numbers of pink salmon {0 ncorliynchus 

 gorbuscha) fluctuate drastically from year to year, 

 and knowledge of the natural processes that cause 

 the fluctuations is required if the resource is to be 

 managed eft'ectively. To evaluate mortality of 

 pink salmon in fresh water, the Bureau of Com- 

 mercial Fisheries has studies in Sashin Creek, a 

 small spawning stream on Baranof Island, south- 

 eastern Alaska. 



Adult pink salmon entering Sashin Creek have 

 been counted each year since 1934, and fry leaving 

 have been counted since 1941. Adults have num- 

 bered from 8 to 92,085 and try from 50 to 

 5,940,300; fresh-water survival has ranged from 

 0.06 to 21.75 percent of potential egg deposition 

 (table 1). 



Only a small portion of Sashin Creek can be 

 used by salmon spawners. Although the Creek is 

 about 4,000 m. long, a waterfall 1,200 m. from the 

 head of tidewater prevents further upstream move- 

 ment of fish. Spawning is limited in a narrow can- 

 yon that extends 300 m. downstream from the 

 waterfall and in the intertidal zone, where the gra- 

 dient is steep and the bottom is mostly bedrock. 

 The main spawning ground (13,629 m.-) lies be- 

 tween the intertidal zone and the canyon. 



Published May 196S. 



FISHERY BULLETIN: VOL. 66, NO. 3 



Four factors that affect survival of pink salmon 

 in Sashin Creek have been discussed by Merrell 

 (1962) and McNeil (1966) : (1) time of migi-ation 

 of sjjawners, (2) distribution of spawners, (3) 

 density of spawners, and (4) weather. To clarify 

 further the relation of these and possibly other 

 factors to survival of eggs, alevins, and fry in 

 Sashin Creek, I studied a relatively large run 

 of pink salmon that spawned there in late August 

 and in September 1965. Sui-vival from deposition 

 of eggs to emergence of fry was estimated in three 

 areas that included 97 percent of the total spawn- 

 ing ground used by spawners in years of large es- 

 capements. 



In this paper, I describe the migration, distribu- 

 tion, and density of pink salmon spawners in the 

 summer of 1965, and the survival of their progeny 

 in fresh water. Also, I discuss: (1) tlie relation of 

 survival of eggs and alevins to time of spawning 

 of adults, (2) variation among stream areas in 

 density of fry, (3) relation of water quality (pri- 

 marily concentration of dissolved oxygen) to sur- 

 vival and development of embryos, (4) disappear- 

 ance of eggs and alevins from spawning beds, and 

 (5) seasonal variation in mortality in spawning 

 beds. 



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