INTRODUCTION 



The objective of conservation research on the Pacific pilchard, or 

 sardine, has been stated by Sette (19'i-3) thus: "To determine for different 

 levels of fishing intensitj'' (i.e., effort), the quantity and quality (sizes 

 of fish) in the average annual catch." The statistical coiaputations in- 

 volved in this determination require a current measurement of the age 

 composition of samples of the comraercial catch. Owing to the close over- 

 lapping in lengths of fish comprising the several ages, it is not feasible 

 to deduce age composition or even to discover with certaintj?- the growth 

 rate by a study of length frequency curves. To attain these ends, it is 

 necessary to employ some other method of determining the age of individual 

 fishes. 



The scales and otoliths of the pilchard, as isi many fishes, are marked 

 with rings Y/hich appear to be related in number to age. As usual ajnong 

 fishes, these marks are not diagramatically clear in the pilchard, being 

 of various degrees of obscurity, and recognition of those that are formed 

 only once annually (the age marks) can be easily confused by the presence 

 of those that are formed fortuitously, the adventitious marks. In a pre- 

 vious reporti' , the authors established criteria for distinguishing between 

 the two types. These were critically tested on .i^^venile material sampled 

 from the bait fisheries of California, and found to serve satisfactorily 

 for determining ages up to the third year. 



It is now proposed to test the application of these criteria to the 

 scales 'Of adult fish as taken in samples of the commercial catch, and to 

 answer this question: lifith what order of accuracy can the age of a pilchard 

 be determined hy recognizing and counting the age marks on its scales? 

 The results of this test and the ansv;er to this question will furnish a 

 basis for judging whether age reading from scales nay confidently be used 

 for age composition records needed in the various studies on this species. 



Thanks are due to our colleagues for their critical attention .ind 

 interest given during the development of this study; in particular, to 

 0. E. Sette, v.rho has suggested a considerable part of the methods that 

 are new. We are grateful also to Dr. H. U. Sverdrup and Dr. Vj. E. Allen 

 of the Scripps Institution of Oceanography, the former for his critical 

 reading of that part of the manuscript touching on oceanographic matters, 

 the latter for making available a large volume of unpublished data on 

 diatom abundance. Vfe are indebted, too, to Julius Phillips, of the Califor- 

 nia State fisheries Laboratory, for his suggestions, cooperation, and 

 criticism. The mounting of scales and a large part of the routine clerical 

 work were done by employees from works Progress Administration projects: 

 765-08-3-22, 65-2-08-286, and 265-2 -08-3U. 



17 



Walford and liosher, 19U3. 



97 



