SEAWARD MIGRATION OF CHINOOK SALMON. 69 



and on the Sacramento River a month or two earher, the exact time varying at different 

 hatcheries and even in different ponds and tanks at the same hatchery. It has been 

 shown above that the most normal time for migration on the Sacramento River is 

 during the latter part of the spring, and on the Columbia River during the latter part 

 of the summer. Therefore, it seems quite probable that these critical periods occur at 

 times when the fry would normally quit the stream in which they were hatched and begin 

 the seaward migration. There may or may not be a causal connection between these 

 two phenomena, but even though the fry were allowed to leave the streams at these 

 times — as the majority will, if permitted to do so — their time of migration would coin- 

 cide well with the normal time observed, and the certain loss resulting from holding them 

 over this critical period would be prevented. There is, of course, the possibility that 

 this loss will occur under any circumstances, but such a conclusion is unwarranted from 

 any data at present available. 



Suggestions, then, as to the care of fry are as follows : 



1. The practice of planting alevins before the complete absorption of the yolk can 

 not be too strongly condemned. No hatchery should be allowed to take a larger number 

 of eggs than can be hatched and reared until the fry are at least ready to feed. Rather 

 than plant the alevins before the yolk has been absorbed it would be infinitely better 

 to allow the eggs which can not be properly accommodated in hatcheries to be deposited 

 normally by the parent fish, and to thus rely upon natural propagation for the outcome. 



2. The liberation of chinook fry at such a time as will enable them to migrate sea- 

 ward at the normal migrating season for the stream in question is advised. This, on 

 the Columbia and Sacramento Rivers, will ordinarily come within about three months 

 after the fry have absorbed the yolk sac and begun feeding. Within this limit it would 

 seem that the longer the fish are held and continue to feed well and grow normally 

 (a point which should be carefully watched) the greater would be their chance for sur- 

 vival. If after several weeks' feeding the symptoms indicative of the approach of the 

 critical period mentioned above appear, it would seem advisable to allow the fish to 

 migrate. Where practicable the fry should not be liberated all at once, but should be 

 allowed to begin the migration gradually and naturally, each fish leaving the parent 

 tributary as the "instinct" to migrate develops. These conditions will be fulfilled if, 

 at the proper time, the screens be removed from the retaining tanks or ponds so as to 

 leave the way clear for the fry to enter the open stream. 



These suggestions are of a general nature only. It is possible that in particular 

 tributaries or in particular regions of a large watershed the conditions and habits of the 

 fish are so different that these suggestions will not apply. In the absence, however, of 

 definite information on these points the practical application of the above suggestions 

 will, as a rule, be found advantageous. 



SUMMARY. 



I. Chinook fry first appear in the Columbia River as early as December of the 

 same year in which the eggs are deposited. By March and April they are fairly numerous 

 in the lower part of the river. Fry appear about two months earlier in the Sacramento 

 River. 



