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BULLETIN OF THE BUREAU OF FISHERIES 
CONDITION OF THE FISHERY 
It is our purpose to discover how the species is faring under the changed condi- 
tions of survival incident to an intensive fishery. In determining this condition we 
must first discover what changes in abundance have occurred. Our only measure 
of the abundance is obtained from the catch of the commercial fishermen which is 
influenced by various economic factors and by changes in the amount and kind of 
gear used. Hence, in determining the actual abundance, as shown by these records, 
one can not use the total catch, but must employ some other measure of abundance, 
such as the catch per unit of fishing effort. Furthermore, the catch of each area must 
be segregated and analyzed separately, for the study of the independence of areas 
(see p. 246) has shown that, in the Pacific herring, the population of each region is 
independent of those of neighboring regions. 
In determining the causes of these changes in abundance within each area a 
knowledge of the size and age composition of the catch is fundamental. In many 
species of fishes, due to variations in hydrographic or other conditions, the amount 
of success attending spawning varies greatly from year to year, it being quite usual 
