FECUNDITY OF THE PACIFIC SARDINE (SARDINOPS CAERULEA) 



By John S. MacGregor, f'ishery Research Biologist 



Extensive studies of the biology of the Paeific 

 sardine {Sarduwps caerulea), designed to lead to 

 an understanding of the causes of fluctuations in 

 the size and distribution of the population, have 

 been carried on since 1949 under the sponsorship 

 of the California Marine Research Committee. 

 These studies, the California Cooperative Oceanic 

 Fisheries Investigations, have been made by the 

 California Academy of Sciences, the California 

 Department of Fish and Game, Hopkins Marine 

 Station of Stanford University, Scripps Institution 

 of Oceanography of the University of California, 

 and the South Pacific Fishery Investigations of 

 the U. S. Fish and Wildlife Service. 



One of the requisites of these studies is a measure 

 of the size of the sardine population. The number 

 of individuals in a spawning population of fishes 

 can be estimated if the following are known: (1) 

 the total number of eggs produced per year by all 

 females in the population, (2) the average number 

 of eggs produced per year by each female in the 

 population and (.3), the sex ratio in the population. 

 This metliod has been one of those used for several 

 years by the South Pacific Fisheries Investigations 

 to estimate the size of the Pacific sardine popula- 

 tion along the coast of California and Baja Cali- 

 fornia. To determine the average number of eggs 

 produced per year by each female it is necessary 

 to determine the average number of eggs spawned 

 per batch and the number of batches produced. 

 The annual egg production per female used in the 

 population estimates has been based on fecundity 

 data for eight female sardines given by Clark 

 (1934). The purpose of the present paper is to 

 record more extensive data on the fecundity of 

 the Pacific sardine (item number 2 above). 



I wish to express my appreciation to my col- 

 leagues, E. H. Ahlstrom and T. M. Widrig for 

 helpful suggestions, F. E. Felin for making the 

 age determinations, A. M. Vrooman for assisting 

 in counting and measuring the eggs and preparing 

 the figures, and W. M. Morton for collecting the 

 material, and to members of cooperating agencies 

 for their assistance. 



Note.- AiiprovcU for puWioUion tVbriiiiry 18, 1957. Fishery Bulletin 121. 



MATERIAL AND EQUIPMENT 



The 13 samples of sardines examined were taken 

 from the commercial fishery at San Pedro, Calif., 

 in November and December, 1945, and January 

 and February, 1946, and included 1,270 individ- 

 uals. These fish, originally collected for a mor- 

 phometric study, were fixed and preserved in 

 formalin in gallon jars. Some of them were subse- 

 quently transferred to alcohol. 



Ovaries and ovary samples for ovum counts 

 and diameter measurements were weighed on a 

 Sartorius Selecta balance. The ovum counts and 

 diameter measurements were made on projected 

 images of the ova using the scale reading device 

 described by Mosher (1950). 



The ovary samples were placed on microscope 

 slides for weighing and projection. Slides were 

 prepared by placing two threads parallel to each 

 other and to tlie long axis of the slide, along one 

 surface of the slide, and securing them at the ends 

 with cellophane tape. The threads were spaced a 

 distance apart somewhat less than the diameter 

 of the microscope field and served as guide lines. 

 The use of threads rather than etched lines kept 

 the ova from falling on the line and controlled the 

 spread of the mounting medium. 



METHODS 



A pair of ovaries was drained for a few minutes 

 on paper toweling and weighed to the nearest 0.001 

 gram. A small sample from one ovary was then 

 placed on a microscope slide and weighed to the 

 nearest 0.0001 gram. A drop of glycerin was 

 placed over the sample; the ova were teased out 

 and spread into three strips separated by the two 

 guide-line threads. A second microscope slide was 

 then placed over the first and the two slides were 

 fastened at the ends with cellophane tape. The 

 formalin-hardened ova were not distorted between 

 the slides prepared in this manner so long as the 

 pressure applied to the slides was not excessive. 

 A second mount was prepared in a similar manner, 

 using a sample from the other of the pair of ovaries. 

 The use of two samples for each pair of ovaries 



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