32 ARTIFICIAL PROPAGATION OF PACIFIC SALMONS. 



necessary facilities exist it is advisable to feed them until they have 

 attained a length of at least 2^ inches, as fish of that size are much 

 more likely than fry to elude their enemies. 



The following information bearing iii)on the ages at which salmon 

 should be planted is taken from reports of Dr. C. H. Gilbert, Pro- 

 fessor of Zoology, Stanford University, on investigations made by 

 him for the U. S. Bureau of Fisheries and for the commissioner of 

 fisheries of British Columbia : 



The blueback spawns normally either in its fourth or fifth year, the chinook 

 salmon in its fourth, fifth, sixth, or seventh year, the females of both species 

 being preponderatingly four-year fish.*' 



The young of both blueback and chinook salmon may migrate seaward 

 shortly after hatching, or may reside in fresh water until their second spring. 

 Those of the first type grow more rapidly than the seccmd, but ai"e subject to 

 greater dangers and develop proportionately fewer adults.*^ 



[In the case of the blueback salmon] examination of scales from all the 

 important blueback streams of the Province has shown for each basin that 

 adult fish are derived from yearling migrants, to the practical exclusion of 

 those which migrate as fry. Out of some 8,000 bluebacks of the 1913 run, 

 only 12 fish seemed with some probability to have developed from fi'y migrants. 

 It would seem, then, that with few exceptions the fry of this species perish 

 after entering the sea. The only alternative to this conclusion is that fry 

 develop in the sea in precisely the same manner, at the same rate, and with 

 all the local peculiarities marking those of their own basin, which develop for 

 a year in their native lake. To one acquainted with all the facts, such an 

 hypothesis appears impossible and absurd.^ 



The deplorable waste occasioned by the loss of vast numbers of fry can not 

 be checked, it would seem, in the case of such progeny as are the result of 

 natural spawning. They can not be held back from migrating as fry if the 

 instinct seizes them. But the case is different in hatchery practice. Here 

 [British Columbia] it is still the custom to release the yoimg as soon as the 

 egg sac is absorbed and free feeding begins. But, in view of the conditions 

 here pointed out, it would appear to be imperative that the fry of the year 

 hereafter should be held in troughs or ponds and fed until midsummer, when 

 the time for downward migration will have passed. They can then be deposited 

 in the lake, with full confidence that they will pass to sea as yearlings the 

 following spring.^ 



Silver salmon spawn normally only in their third year. The young migrate 

 either as fry or yearlings, but adults are developed almost exclusively from 

 those which migrate as yearlings.*^ 



Chum salmon mature normally either in their third, fourth, or fifth year; 

 humpback salmon always in their second y(>ar. The young of both species pass 

 to sea as soon as they are free swimming.* 



The term " grilse " as used for Pacific salmon signifies conspicuously undersized 

 fish which sparingly accompany the spawning run. They are precociously 

 developed in advance of the normal spawning period of the species. So far as 

 known, the grilse of the chinook, silver, and chum salmons are exclusively 

 males, of the blueback, almost exclusively males, except on the Columbia 

 River, where both sexes are about equally represented. The larger grilse meet 

 or overlap in size the smaller of those individuals which mature one year later 

 at the normal period.** 



The great differences in size among individuals of a species observed in the 

 spawning run are closely correlated T,\ith age, the younger fish averaging con- 

 stantly smaller than those 1 year older, though the curves of the two may 

 overlap.** 



« Gilbert, C. IT. : Age at maturity of the Paoiflc coast salmon of the genua Oncorhyn- 

 chus. Bulletin, TJ. S. Bureau of Fisheries, Vol. XXXII, for 1912, pp. 21-22. Washington, 

 1013. 



I* (JillKTt, r. II.: Summary of Contributions to the lifo-history of the sockeye salmon. 

 (No. 1.) British Columbia. Report, Commissioner of Fisheries, for 1913. pp. IllO-Rll. 

 Victoria, 1914. 



