Length Composition of California Commercial Catch 

 of Pilchard, 1919 to 1951 



By 



Margaret M. Calderwood 



The data contained in this paper have been compiled from source 

 files and are presented for use by fishery scientists for study of 

 complex relationships which exist between age classes of a pelagic 

 fishery. Knowledge of the relative size of each age class present in 

 the population is required before changes can be determined . This 

 knowledge is usually obtained by analysis of samples taken from the 

 commercial catcho From this the history of each age class is developed 

 and presented in the form of catch curves (Baranoff, 1918) o 



During the period of the California sardine fishery for which there 

 are no data from tagging or from age determination, the length composi- 

 tion of the catches provides the only source of data from which catch 

 curves may be derived. 



Sardine length data have been shown by Silliman (19u5) to be appli- 

 cable to a period, before 1933 3 of lower fishing intensity for sardine 

 when his estimate of total annual mortality amounted to 20 percent . 

 Silliman also estimated the sources and degree of error in mortalities 

 calculated from length composition as compared with certain populations 

 having known mortality rates. He concluded (p„ 195) that "at mortality 

 rates of up to about 20 percent per year the error is negligible, but 

 increases rapidly with increasing mortality rate above 20 percent. For 

 this reason it is fortunate that other methods are available for the 

 higher mortality rates prevailing under recent levels of exploitation." 



For periods during which age data are available from spot samples 

 only, or from incomplete collection, e.g., of otoliths (Hosher, in 

 press), the age composition of small samples may be applied to the more 

 representative samples of length composition of catches throughout a 

 season in order to obtain an estimate of the age composition of the 

 catch (Eckles, in press). 



When age data for the catch are not available, length frequency 

 data may further be useful in following changes in size and growth at 

 various fishing intensities. 



The following series of tables represents the length composition, 

 so far as obtainable, of the commercial catch of sardines, Sardinops 

 caerulea (Girard) 185U, in California from the 1919-20 through the 

 1950-51 s eas on . 



