368 ANNUAL REPORT SMITHSONIAN INSTITUTION, 193 5 



miles away, off the coast of Washington. But these exceptions were 

 so few as not to upset the general conclusions. 



The findings were checked by other methods. For instance, that 

 used by the anthropologist to distinguish races was applied. Thou- 

 sands of fish were carefully measured, and physical characters such 

 as length of head were found to differ from bank to bank. And, 

 again, comparison of the rates of growth showed them to be very 

 different on different banks. It was apparent that these peculiar 

 characteristics could not have persisted unless the stocks had been 

 isolated, at least during the growth of the individuals. 



When these stocks of fish had been properly distinguished, it 

 became possible to separate into proper units the splendid statistics 

 gathered by the Commission as to the yield of the fishery. Those 

 for each separate stock of fish could be combined and analyzed. 

 Where before the steady increase in the number of stocks utilized 

 had masked the changes occurring, and where before contrary ten- 

 dencies in two stocks had balanced and obscured each other, now it 

 could be seen that the yield in each individual stock was behaving 

 in an orderly consistent way. 



So well defined and simple were the laws governing the behavior 

 of these stocks that it was possible for the Commission to understand 

 what was happening on the banks. Knowing the intensity of the 

 fishery it could reconstruct the course of events with sufficient ac- 

 curacy to provide a forecast from year to year and to point decisively 

 to the type of regulation necessary. 



But these laws that seemed now so apparent were simple only 

 when certain biological facts were Imown. In the first place, the age 

 had to be known accurately, because the age is a time scale according 

 to which the great changes in the fishery progress. Removal by 

 fishing, death, or emigration takes place at certain variable rates, 

 annually, and each age class as it enters the stock is decimated and 

 finally disappears in accord with these rates. Its age represents the 

 time during which these rates have been operating. In the second 

 place, these rates of death, of growth, and of migration had to be 

 known. The two categories of facts, time or age and rate of change 

 in vital processes, are essential; age in itself is of little significance. 



The age and rate of growth were determined by fascinating meth- 

 ods developed in recent years and around which a large body of 

 scientific literature has grown. Many of the harder parts of the fish 

 grow by addition to what has already been formed. Thus in the 

 scales new growth occurs around the margins month by month dur- 

 ing the year. Rapid gi-owth is shown by a structure different from 

 that of slow growth. As in the case of trees, fish undergo changes in 

 their rates of growth according to the season. They are cold- 

 blooded and change temperature and rate of metabolism with their 



