6 ARTIFICIAL PROPAGATION OF PACIFIC SALMONS. 



100 miles a month. As the season advances the rate of progress up 

 the rivers is more rapid. 



The spawning season varies in different rivers and covers a period 

 of at least four months. The spring run begins to spawn at the head- 

 waters of the Willamette and Salmon Rivers, tributaries of the 

 Columbia, in August, while the summer run at the Little White 

 Salmon and Big White Salmon stations, nearer the ocean, be^ns 

 spawning about September 20. At the Clackamas (Oreg.) station, 

 eggs are secured from the fall run from the last of September to 

 about December 1. 



For the deposition of their eggs chinook salmon invariably seek 

 a shallow, gravelly riffle, where the water is a foot or more deep, 

 and the current sufficiently swift to carry and spread the eggs and 

 milt. There is no doubt that in many instances the so-called nest, 

 which is an elongated cavity or depression, often several feet across 

 and 12 or more inches in depth, is started by either the male or female 

 in advance of actual spawning, but as a general thing it is formed 

 by the fish in the act of spawning. At this time both the male and 

 female turn on their sides and by contraction of the abdominal 

 muscles, which produces a quivery motion of the body, effect the 

 simultaneous emission of milt and eggs. At about the same time 

 a forceful movement of the tail and posterior part of the body serves 

 to loosen the gravel and propel the fin forward more or less, thus, by 

 frequent repetition, enlarging the depression and covering the eggs 

 with the loose gi^avel. It seems evident that this is nature's provision 

 for the protection of the eggs, during the incubation period. With 

 every effort made by the fish in the extrusion of the eggs and milt 

 the depth of the covering is increased, and this serves not only to 

 screen them from the light, which is conducive to the growth of 

 fungus, but also protects tliem from the prying eyes of trout and 

 other active aquatic enemies. 



The length of time consumed in spawning is largely governed by 

 the num})er of eggs a female contains and also b}' the temperature of 

 the water. In some instances all of the eggs will be deposited within 

 a day or two, while in others spawning will extend over a period 

 of a week or 10 days. 



Both the eggs and the fry are subject to destruction by freshets 

 Avashing them out of the gravel or covering them so deep that, if they 

 are not actually killed by the pressure on them, it becomes impossible 

 for the fry to work their way out. In many streams spawning occurs 

 during high-water stages in the fall, the eggs in numerous instances 

 being deposited in gravel which is entirely above the water later in 

 the season. Many eggs are lost also by trout' lying close in behind 

 the salmon and catching them as they are emitted. Some are rooted 

 out of the nest, and the natural enemies take their toll as the fry 

 emerge from the gravel. It is the instinct of the fry to lie quiescent 

 until the umbilical sacs have been absorbed, when they leave the nest 

 in search of food. 



Experiments conducted some years ago by John P. Babcock ^ have 

 demonstrated clearly that only those eggs in natural spawning which 

 are embedded beneath from 5 to 6 inches of sand and gravel produce 



« Romo exppriments in the burial of salmon eggs, suggesting a new method of hatching 

 salmon and trout. Tr.'nsactions, American Fisheries Society for 1910, pp. 393-395, 

 Washington, 1911. 



