PACIFIC HERRING 
293 
to have periods of years when but few young survive, and occasional years in which 
exceptionally large numbers of young survive. These unusually abundant year 
classes, termed “dominant” year classes, have been found in the cod, the plaice, the 
mackerel, and in the very close relations of the Pacific herring— the California sardine 
(Higgins, 1926; Scofield, 1926) and the Atlantic herring (Hjort, 1914; Lea, 1919, 
1924) — and the presence of these dominant year classes causes natural fluctuations 
in abundance. A temporary decline in abundance, due to the passing out of the 
catch of a dominant year class, must not be confused with a decrease due to over- 
fishing. Therefore, in attempting to explain the fluctuations in abundance of the 
Figube',34. — Total weight, cleaned weight, and gonad weight for herring in Halibut Cove and lower 
Kachemak Bay for 1927 
Pacific herring, one of our first aims was to demonstrate the existence or nonexistence 
of this phenomenon of dominant year classes and its effect on the catch. 
COMPOSITION OF THE CATCH 
SAMPLING FOR SIZE AND AGE COMPOSITION 
In order to connect the changes in the composition of the catch with fluctuations 
in the yield of the fishery, it is necessary to follow such changes as may occur in the 
size and age of the population. 
For this knowledge of the herring population we must depend upon the portion 
taken by the fishermen. Of this portion consisting of many thousands of barrels 
of fish only a few thousand individuals can be measured. Hence, the question natur- 
ally arises, How accurately do these few individuals represent the population? 
