PROGRESS IN BIOLOGICAL INQUIRIES, 1939 47 
season, by district. Indices of abundance and seasonal time of ap- 
pearance of the salmon runs are determined from these daily aver- 
ages. This information is used as a basis for recommending changes 
in the fishing regulations in Alaska in order to provide for the 
conservation of the salmon resources. 
During 1939 the records from the Alaska Peninsula, Chignik, 
Kodiak Island, and Cook Inlet trap fisheries were sorted and indexed. 
The tabulation of these data will be begun in the near future. 
HERRING 
Three major areas of the Territory of Alaska at present support 
extensive commercial herring-fishery operations; these being Kodiak, 
Prince William Sound, and Southeastern Alaska. The investigation 
of the herring fisheries, which was continued throughout the year 
by E. H. Dahlgren and L. Kolloen, was primarily concerned with 
the following problems: The delimiting of the areas frequented by 
the various races or populations comprising the stocks of herring; 
an evaluation of the abundance of the populations supporting each 
of these fisheries; the measuring ot changes in fishing intensity; and 
the determination of fluctuations in annual increments to the popu- 
lation, and the factors governing these fluctuations. 
Kodiak area—In the Kodiak area the largest catch ever recorded 
was made in 1939, with a total take of 309 000 barrels. However, 
the total catch of itself has no significance as a measure of abundance 
unless correlated with the fishing effort required to make it. Since 
the inception of reduction oper ations in this area in 1935, the herring 
fishery has undergone a tremendous expansion. Reduction capacity 
has increased from 15 tons of raw fish per hour in 1935, to 45 tons 
per hour in 1939; the number of vessels engaged has increased from 
11 to 21; and, with a tendency toward the use of larger vessels, the 
fishing capacity of the fleet has increased threefold. In order to 
establish a trend of abundance, the number of vessels, weighted by 
their net tonnage in order to account for the greater efficiency of 
larger vessels, multiplied by the number of days each vessel operated 
in the area, was divided into the total catch for the year to give the 
average catch per ton-day of fishing effort. These ‘data were com- 
piled for each year since the inception of the reduction industry im 
1935. The catch in barrels per ton-day fished rose from 6.4 in 1936 
to a high of 7.5 in 1937 and has declined to a low of 4.5 in 1939. 
The great abundance of herring in the Kodiak region during the 
past 5 years has been in part the “result of the ac cumulations of the 
stocks during the less intensive operations previous to 1935. A fur- 
ther factor that contributed to the high abundance level has been the 
presence in the catch of the offspring of the dominant 1931 year-class. 
The phenomenon of dominance of certain year-classes, with the 
attendant great natural fluctuations in abundance, results from an 
occasional remarkably successful spawning, in consequence of which 
large numbers of larvae survive to enter the adult populations 3 years 
later. In contrast, spawnings in immediately previous or subsequent 
years are not so successful—some may even be virtual failures and 
contribute no appreciable increments to the stocks. Daily samples of 
the catch were taken throughout the season and ages were read 
