During the pilchard spawning season of 1940 the United States Fish and Wildlife Service, in collaboration with the Scripps Institution of Oceanography, made periodic surveys of part of the pilchard spawning area in an attempt to make quantitative evaluations of egg deposition. In addition to estimating the number of eggs deposited in the entire survey area during the season, it was desired to make estimates of the number of eggs for parts of the area or season in connection with studies of survival, drift of larvae, etc .
Silliman, Ralph P.. 1946. "A study of variability in plankton townet catches of pacific pilchard (Sardinops caerulea) eggs." Journal of Marine Research 6, (1). https://elischolar.library.yale.edu/journal_of_marine_research/625