SUCCESS OF PINK SALMON SPAWNING RELATIVE 

 TO SIZE OF SPAWNING BED MATERIALS 



by 



William J. McNeil, Research Associate 



and 



Warren H. Ahnell, Research Assistant 



Fisheries Research Institute, College of Fisheries 



University" of Washington, Seattle, Washington 



ABSTRACT 



The potential of a salmon spawning bed to produce fry is directly related to its 

 permeability. The relationship between the coefficient of permeability and the frac- 

 tion of bottom materials consisting of fine particles is inverse. 



Field methods for measuring size composition of bottom materials in salmon 

 spawning beds are described, and an empirical relationship between the fraction 

 (by volume) of solids less than 0,833 mm. minimum dimension and the coefficient 

 of permeability of stream bottom materials is given. Size of bottom materials in 

 streams utilized for spawning by pink salmon (Oncorhynchus ^orbuscha) varied con- 

 siderably. The more productive spawning streams had the more permeable spawning 

 beds. Adult pink salmon caused the removal of finer particles from bottom mate- 

 rials during spawning. The evidence indicates that the fine particles removed 

 consist largely of organic matter. Logging caused fine sands and silts to accrue 

 to spawning beds. Flooding caused the removal of fine particles from spawning beds. 



INTRODUCTION 



Pink salmon (Oncorhynchus gorbuscha) are 

 the most abundant of the Pacific salmon and 

 in most years provide a larger commercial 

 catch than the other species. In the eastern 

 Pacific, pink salmon are of commercial im- 

 portance from Bristol Bay, Alaska, to Puget 

 Sound, Wash. They are of greatest importance 

 in Southeastern Alaska where there are about 

 1,100 spawning streams (Martin, 1959). 



Note--William J. McNeil is now with tiie Bureau of 

 Commercial Fisheries, Auke Bay, Alaska; Warren H. 

 Ahnell is now at Washington State University, F>ullman, 

 Wash. 



A critical period in the life history of pink 

 salmon occurs between the time eggs are de- 

 posited in spawning beds of streams and the 

 time fry emerge several months later. Adult 

 females excavate pockets in gravel beds and 

 cover their eggs with 3 to 15 inches of gravel. 

 This action affords eggs and larvae protection 

 against predators, mechanical injury, and 

 displacement by flowing water. Other environ- 

 mental stresses are encountered, however, 

 and mortality within the streambed commonly 

 exceeds 75 percent. 



The growth, development, and survival of 

 salmon eggs and larvae are dependent on 

 physical and chemical characteristics of the 

 surrounding water. These properties include 



