Figure 2. -Pink and chum salmon fry that have just emerged from the streambed. The pink salmon are distinguished by their 

 smaller size and the lack of the parr marks that are noticeable on the backs of the chum salmon fry. In these live fish the 

 fins arc nearly transparent because they are very thin and unpigmented. 



and a new egg pocket is formed to receive the next clus- 

 ter. Sand and gravel protect the eggs from sunlight, floods 

 and predators, and the female protects them from being 

 dug up by other females who are digging their own redds. 



Pink salmon are somewhat inefficient at burying their 

 eggs in the streambed; some of this inefficiency can be 

 traced directly to the density of the spawners. When too 

 many females are present, some frequently dig up eggs 

 that are deposited by other females, and some may not 

 be able to deposit all of their eggs before they die. 



Males and females both die soon after they spawn. 



Survival 



A mature female pink salmon usually has about 2,000 

 eggs, but if only two of these survive to return as mature 

 spawners the population will be perpetuated. The life 

 history of pink salmon occurs in three physically and 



biologically distinct environments-streams, estuaries, and 

 the ocean-and biologists have studied survival in each 

 environment. In the stream less than 25 percent of the 

 eggs survive from the time of spawning to the time of 

 emergence from tiie gravel. The principal causes of the 

 death of salmon eggs are ( 1 ) digging in the redds by other 

 females, (2) low oxygen supply because of low stream- 

 flows or impairment of water circulation within the 

 streambed, (3) dislodgment of eggs by Hoods, (4) freez- 

 ing of eggs during periods of severe and prolonged cold, 

 and (5) predation by other fish. Less is known about 

 survival in the other two environments, but indications 

 are that about three-fourths of the fry entering the estu- 

 ary are lost before they reach the ocean and that of those 

 reaching the ocean, about three-fourths die before they 

 attain maturity. Predation is believed to be the principal 

 cause of death in the estuary and at sea. 



