60 REPORT OF THE FISII AND GAME COMMISSION. 



requirements of those in the industry, that the present fishing is not 

 causing depletion and that the fluctuations in abundance from season to 

 season are due to natural causes. The analysis of the relative abun- 

 dance of albacore during past years, as made by this commission and 

 published in the Pacific Fisherman Year Book 1919, showed a steady 

 fall in the catch of the same unit of gear from year to year. Based on 

 that evidence alone this would indicate depletion, but from other facts, 

 mainly that the proportion of older fish caught at the latter end of the 

 season, held up, we are led to believe that the fall in relative abundance 

 of albacore during these years was not due to depletion but to natural 

 causes. This conclusion is borne out by the fact that the catch for 

 1920 has shown a decided increase, which coupled with the reappearance 

 of younger classes of albacore are encouraging signs. 



A necessary part of such a fisheries investigation is to work out a 

 method of determining the age and rate of growth of the fish. It is of 

 great importance to be able to determine the relative abundance of the 

 age classes of the fish under investigation, in order that depletion may 

 be distinguished from natural fluctuations in abundance and to furnish 

 information upon which to predict the abundance in the future seasons. 



The work on the age and rate of growth of the albacore has pro- 

 gressed to where it is now ready for publication. The usual method 

 of determining age is by means of the marks or winter checks on the 

 scales. These marks proved to be extremely difficult to decipher by the 

 simple method of viewing them through the microscope. A special 

 technique was used to decipher them which entailed a great amount 

 of painstaking labor. The method is a distinct contribution to the 

 science of fisheries conservation for it proves by a strictly mechanical 

 method which is entirely free from the Influence of the workers personal 

 judgment that the marks on the scales correspond absolutely with the 

 age of the fish. The importance of this contribution will be seen when 

 it is known that well known biologists have expressed their doubt if the 

 marks on scales do actually show age. This is the first direct knowl- 

 edge we have of the age of any of the fish belonging to the mackerel 

 family. 



The work on the age of albacore shows that it is a fast growing 

 fish, which is encouraging, for on that account the fishery can stand 

 heavier fishing than if it were a slow growing fish. The .study of age has 

 also thrown light on the migration of these fish. These matters are 

 thoroughly discussed in Mr. Thomp.son's paper. 



Much work has been done on the migrations and fluctuations in the 

 run of albacore. A relationship between the catch and temperature, 

 or some factor allied with temperature, has been shown. A couple of 

 papers by Mr. Thompson have already pointed out this relationship. 



