64 KENDALL: NEW ENGLAND SALMONS. 



this arrangement must undoubtedly be of the highest value as a means of protecting 

 the species. It would indeed be difficult to conceive of any device that is so admirably 

 suited for the distribution and neutralization of the risks to which the individual fry of 

 each year are subject.' 



But this 'arrangement' cannot be fortuitous. It must be in conformity to the law of 

 cause and effect. Therefore if there are sufficient reliable statistics it would seem that the 

 fluctuations in the catches of salmon would necessarily be an index to the quantity of 

 salmon present in a given region, and that the quantity present would be a reflection 

 from previous spawnings. 



Referring to Dahl's chart, in order to picture the whole situation during those seven 

 years, among other things, the fish resulting from the smolts of the year mentioned will 

 be augmented by fish resulting from smolts of preceding and succeeding j^ears. The 

 chart represents smolts migrating at the ages of two to five years, each returning as 

 maiden fish after one to four years in the sea, in a period of seven years. Each generation 

 expires with the oldest salmon. Assuming that spawning runs of salmon resulting from 

 smolts which had migrated in the four years preceding 1903 were small, and that of 1903 

 was large and successfully reproduced, naturally it would be expected, other things being 

 equal, that one of the years from 1907 to 1910 would be a good one. If the largest pro- 

 portion of smolts of a given river were two years old when they migrated and the largest 

 return of maiden fish six-year-old fish, it would seem logical to look for a good run in 

 1910, and according to the chart that is what would have occurred, for all ages of that 

 generation are represented, and by fish of three other generations as well. 



From aU that has been learned concerning the hfe history of the salmon, it is quite 

 evident that the salmon of difi'erent rivers differ more or less from each other in that 

 respect, and, as has been said, the river hfe of the young salmon reacts on the sea life 

 of the adult as to the time at which it shall return to the river. Whatever may be the 

 factor or factors determining the dominance of a particular age-class of smolts, the 

 volume of a salmon return would depend, at least in part, upon age-classes of the fish 

 composing it, for naturally the younger fish would be the most numerous in the aggregate. 

 This is demonstrated in the case of rivers characterized as 'grilse' rivers. Again it has 

 been shown that the greater proportion of returning salmon which have spent more than 

 one winter in the sea is composed of two age-classes or one or the other of two, according 

 to the river. 



It, however, has been shown that it does not necessarily follow that all fish which have 

 spent only one winter in the sea return as grilse. Therefore a run of grilse may be of one 

 age-class onlj^ or there may be no grilse or relatively few of them, if any. The age-class 

 which does not return the following year contributes to the 'reserve' stock mentioned by 

 Dahl. But, on the other hand, Dahl's chart indicates that all ages may periodically be 

 present in one year. Therefore, it would seem that there might be periods of abundance 

 or scarcity having origin in a continued dominance of one age-class of smolt. It is only 

 a step further to perceive the possibiUty of the 'divided migrations' and early and late 

 runs as having some relation to the dominant age-class of parr and smolt. 



