EFFECT OF THE SPAWNING BED ENVIRONMENT ON REPRODUCTION 



OF PINK AND CHUM SALMON ' 



By William J. McNeil, Fishery Biologist (Research) 



Bureau of Commercial Fisheries Biological Laboratory 



Auke Bay, Alaska 



ABSTRACT 



Mortality of 5 brood years of pink salmon, Oncorhyn- 

 ch us gorbuscha, and chum salmon, 0. keta, in spawn- 

 ing beds of three Southeastern Alaska streams was 

 studied. Eggs and larvae were sampled periodically, 

 and mortality was associated with certain environ- 

 mental factors: The supply of dissolved oxygen, the 

 stability of spawning beds, and freezing. 



Total mortality between spawning and fry emergence 

 typically varied between 75 and 99 percent in the study 

 areas. High mortality occurred during low and high 

 stream discharge and freezing air temperatures. Mor- 

 talities ranging from 60 to 90 percent of deposited eggs 

 occurred in association with low dissolved oxygen levels 

 during and after the spawning period. Movement of 

 gravel in certain instances was associated with the 

 removal of 50 to 90 percent of eggs and larvae present 



in spawning beds. Freezing caused up to 65 percent 

 mortality of eggs and larvae in one stream. 



Low dissolved oxygen levels occurred once in 5 years. 

 This occurrence was associated with unusually low 

 water during spawning in late summer. Mortality 

 during periods of heavy precipitation was highly vari- 

 able. In one instance, a 90-percent mortality occurred 

 where wood debris was deposited within the high water 

 channel. Wood debris floating over spawning beds 

 was not damaging to eggs and larvae. There were 

 several instances where mortality estimated at almost 

 50 percent occurred with no evidence that deposited 

 wood debris shifted position. High mortality from 

 freezing occurred only in the stream having the lowest 

 minimum discharge. 



Pink salmon, Oncorhynchus gorbuscha, and chum 

 salmon, 0. keta, are the only species of Pacific 

 salmon in North American streams using fresh 

 water 2 solely for spawning. The young of these 

 species, with minor exceptions, migrate to sea soon 

 after emerging from spawning beds, while the 

 young of chinook salmon, 0. tshawytscha; soc.keye, 

 0. nerka; and coho, 0. kisutch, may remain in 

 fresh water for many months. 



Note. — Approved for publication Nov. 19. 1964. 



1 This research was done while the author was a Research Associate at the 

 Fisheries Research Institute, University of Washington, Seattle, Wash, 

 and was financed by the Bureau of Commercial Fisheries under Contract 

 Nos. 14-17-008-29, 14-17-008-96, 14-17-0005-20, and 14-17-0005-31, with funds 

 made available under the Act of July 1, 1954 (68 Stat. 376), the Saltonstall- 

 Kennedy Act. This report constitutes Contribution No. 198, College of 

 Fisheries, University of Washington, Seattle, Wash. 



2 Includes intertidal areas periodically inundated by salt water or brackish 

 water. 



Adult pink and chum salmon commonly migrate 

 into coastal streams to spawn in summer and early 

 autumn. They excavate pockets in riffle areas 

 and deposit and bury their eggs in the bottom. 

 Surviving embryonic and larval salmon remain in 

 the spawning bed for periods up to 8 months, and 

 fry usually emerge and migrate seaward the spring 

 after spawning. 



The spawning bed protects eggs and larvae 

 against predators, light, displacement, and me- 

 chanical injury. Despite this protection, mortal- 

 ity from time of egg deposition to fry emergence 

 commonly exceeds 75 percent. 



Estimates of total fresh-water mortality of pink 

 and chum salmon have been published for Mc- 

 Clinton, Morrison, Nile, and Hook Nose Creeks, 

 British Columbia (Pritchard, 1948; Neave, 1953; 



FISHERY BULLETIN: VOLUME 65, NO. 2 



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