32 



BULLETIN OF THE BUREAU OF FISHERIES 



liberate larger numbers of young at a smaller size. In this, also, we are without facts 

 to determine the problem. In one important respect the advantage would seem to 

 lie with hatchery practice, for in pond life the young are protected from predaceous 

 enemies and would appear thus to enjoy a signal advantage over wild stock spending 

 an equal time in fresh water; but this is not the whole story, for the pond-reared fish 

 are in turn exposed to certain dangers, due to crowding in limited quarters and to 

 prolonged artificial feeding, from which the wild stock are exempt. No reliable 

 statistics are available concerning the mortality incident to pond culture. When 

 these have been secured we shall have made a beginning toward the solution of 

 this most important problem in fish propagation. 



As is true generally with the young of the red salmon, those of the Karluk race 

 disappear on reaching salt water and roam the seas without detection until, after 

 having spent varying periods in the ocean, they seek the river once more at spawning 

 time. As will appear below, they mature at various ages ranging from 3 to 8 years, 

 spawn but the once, and then perish. The list of the various age groups follows, con- 

 sidered in connection with the classes of fingerlings from which they develop. 



These classes are five in number, as has appeared from the above sketch of their 

 history, and are based on age at time of migration. They will be numbered from 1 to 

 5, the No. 1 group comprising the migrant fry in their first year, and the groups 

 numbered from 2 to 5 representing those that migrated in their second third, fourth, 

 and fifth years, respectively. This division will reappear in our analysis of adult 

 runs and will form the basis of primary groups founded on length of residence in 

 fresh water before migrating to sea. The secondary divisions are based on the num- 

 ber of years spent in the sea before maturing, and this varies in each primary group. 

 Thus, the members of group 1, both males and females, mature and return to the 

 river either in their third year of sea feeding or in their fourth. As they entered the 

 sea during their first year after hatching, they are in their third or their fourth 

 year at time of maturing. We designate these two age groups by the symbols 3i and 

 4 1, the first figure in each case representing the age at maturity, and the second the 

 year of its life in which it migrated from fresh water. 



The members of group 2 likewise mature in their second, third, or fourth year in 

 the sea, and are therefore in their third, fourth, or fifth year of age at maturity. 

 They are here designated as the 3 2 , 4 2 , and the 5 a age groups (figs. 31 and 32). 



Group 3 comprises the great majority of the youthful migrants, and furnishes the 

 largest age groups among the adult fish. A rare individual of this group, always a 

 male fish, is known to mature during its first season at sea while still in its third year, 

 having spent but a few months on the sea feeding grounds. These diminutive 

 "grilse" range from 30 to 40 centimeters long; and as they readily pass through the 

 meshes of the seine used in the capture of the commercially valuable part of the run, 

 they easily escape notice. (See fig. 25.) A larger size of grilse, belonging to group 3, 

 is one year older than those above mentioned and returns in its second season in the 

 sea as 4-year fish. These are still largely, but not exclusively, males, and are under- 

 sized fish of little value. The members of group 3 do not attain their full size and 

 become commercially valuable until their third year in the sea, when they are in 

 their fifth year. (Fig. 28.) The great majority of them always mature at this age, 

 and they constitute always the great bulk of the commercially valuable run. A 



