66 BULLETIN OF THE BUREAU OF FISHERIES 



stances shoiild operate to increase the survival (and therefore the spawning run) in 

 any year, the effect of such an increased run would not necessarily be felt in future 

 years, as the area occupied by the race will not, in general, accommodate a population 

 greater than the normal maximum capacity. On the other hand, if the general level 

 of abundance be reduced materially by fishing, this level will be below the potential 

 capacity of the area, and then an increase in abundance in one year can have a very 

 definite effect upon the future generations and would start a series of years marked 

 by good runs separated by years of ordinary runs. The interval between the good 

 years would be determined by the prevailing age at maturity of the race in question — 

 more particularly, perhaps, by the prevailing age of the females. Somewhat similar 

 results would follow the occurrence of a year in which survival was reduced. Under 

 natural conditions the abundance of fish resulting from a poor year would be below 

 the normal capacity of the area, and we may suppose that the race would react by 

 an increased survival of the progeny of the reduced spawning run, so that the size 

 of the resultant spawning runs would tend to approach the normal level. It seems 

 possible that the effect of a very poor year might be felt for one or two generations 

 while building up to the normal level, in contrast to the effect of an unusually good 

 year, wliich, on account of the lunitation imposed by the capacity of the occupied 

 area, could not greatly affect the future runs. Under conditions of exploitation, 

 however, a poor year will tend to be perpetuated, just as in the case of a good year, 

 but for a different reason. The perpetuation of a good year is dependent upon what 

 we may term the elasticity of the race — the tendency to approach the normal level 

 of abundance; but the perpetuation of a poor year will depend mainly upon the 

 continuous application of a fishing effort sufficient to keep the spawning escapement 

 down to a low level. There is no doubt that fishing operations ordinarily operate so 

 that the spawning escapement in good years is better in proportion than in poor 

 years, which is just the reverse of what sensible conservation would call for. On the 

 other hand, it seems probable that the lower the actual level of abundance the 

 stronger the tendency of the race to resist further lowering and the greater the 

 tendency to return toward the normal level of abundance. In other words, as the 

 level of abundance drops there is a tendency toward an increased survival rate. 

 This is well illustrated by the present situation on the Karluk River. It has been 

 shown ^ that the present production from the spawning escapements is approximately 

 300 per cent; that is, for each spawning fish three adults may be expected to return 

 in future years. Under natural conditions the production in general is 100 per cent, 

 of course. This increased percentage of production is exactly what we would expect 

 in the case of a depleted rim such as that in the Karluk; but however strong this 

 tendency toward an increased percentage productiveness at the lower levels of 

 abundance may be, it is impotent in the face of intensive fishing. It may operate to 

 retard the depletion of the poor years, but without some relief from intensive fishing 

 it can not rebuild poor years into good ones or even average ones. 



The chief contention in the above argument is to the effect that cyclic fluctua- 

 tions are associated especially with the exploitation of a fishery, and that under 

 natural conditions such fluctuations would not be so conspicuous. However, there 



' Investigations Concerning the Red-Salmon Runs to the Karluk River, Alaska. By Charles H. Gilbert and Willis H. Rich. 

 Bulletin, U. S. Bureau of Fisheries, Vol. XLIII, 1927, Part II, pp. 1-69, 34 flgs. Washington, 1927. 



