PROGRESS IN BIOLOGICAL INQUIRIES, 1939 of 
STUDIES OF ABUNDANCE 
According to a study of the catches of a fleet of purse seiners 
which were delivered primarily to reduction ships on the high seas 
off the coast of central California, the abundance of pilchards in 
that area has undergone a fluctuation; increasing slightly less than 
twofold from the season of 1932-33 to that of 1984-35. During the 
succeeding 3 seasons it decreased by about 70 percent, and in the 
last year, 1938-39, it increased again by about 15 percent. 
An essentially similar course has been demonstrated by the study 
conducted by the California State Fisheries Laboratory on the shore 
landings at the ports of Monterey and San Pedro. Therefore, it was 
evidently a condition effective generally in the waters off California. 
Obviously, the initial rise during this period was due to the entrance 
of a successful year-class, or group of year-classes, probably 2 in 
number, produced in the spawning seasons of 1930 and 1931. The 
subsequent downward trend in the curve, a matter of 30 percent per 
annum, represents the decline of a population dominated by these 2 
year-classes, to which there were no important new accessions. By 
itself, 30 percent per annum has little significance, but must be com- 
pared either with a previous or a future cycle of the passage of a 
successful year-class or group of year-classes through the fishery. 
Unfortunately, the manner of regulating the fishery in previous 
years, enforced in part by the State and in part by the mdustry, 
makes it difficult to obtain a parallel statistic for previous com- 
parable cycles. However, judging from the high percentage of the 
young, coupled with the large catch of the current season, it appears 
that a new cycle has now begun and will soon afford the desired 
comparison. 
In Washington and Oregon the fishery for pilchards has a history 
too short to cover the same period as that studied for California. 
The available records, as analyzed by Vernon E. Brock, of the 
Oregon Fish Commission, in collaboration with O. KE. Sette, per- 
taining to the summers of 1935 to 1938, inclusive, did not show a 
decline similar to that noted from the California records, but rather 
an oscillation about the horizontal trend; the years 1935 and 1937 
being high, and the years 1936 and 1938 being low. This is a some- 
what surprising result in view of the finding by both British Colum- 
bia and California investigators that pilchard migrate between Cali- 
fornia and British Columbia waters. Hence, fluctuations should be 
similar, even at these extremes of the range, provided the entire 
population migrates. The only inference to be drawn from the lack 
of similarity in the results from the north and south is either that 
a varying proportion of pilchard migrates to northern waters each 
summer, or that availability in the north fluctuates so strongly that 
the commercial fishery cannot reflect changes in general abundance. 
A longer series of observations must be awaited before conclusions 
on these points can be reached. 
AGE AND GROWTH 
The identification of year-classes, and the measurement of their 
relative strength, involves a knowledge of past survival rates of 
young fish, which can become known by determining the age of fish 
