suiaaRY km coiiclusions 



Annual rings appear on the scales of adult pilchards, as in the young, 

 and at the sane tirac of year, namely, the v>rinter and early spring. If the 

 scales be properly prepared, those rings can bo recognized and distinguished 

 from false age marks by means of criteria set up in this study. The ac- 

 curacy of following these criteria differs among readers and for different 

 ages of fish being lower for older ages than for younger ones, but for the 

 age distribution prevailing from 1939 to 19U2, and for the persons reading 

 the scales in this study, it averaged near to 93 percent. 



The most important evidence supporting the validity of age determina- 

 tion by scales is that the fish allocated to each year class had growth char- 

 acteristics In comraon, v/-hich appeared consistently in three seasons of sam-> 

 pling. These characteristics were expressed as the average first year's 

 growth increment, calculated from scales. Departures of these averages 

 from a norm v;ero significantly correlated with anomalies in certain" elements 

 of the environment, thereby proving that the identification of the year 

 classes had been correct. 



The correlations indicated that, in general, grovfth during the first 

 year is favored by a sustained presence of diatoms v at optimum abundance. 

 In turn, the latter is favored by upwelling, v/hich is induced by northwest 

 T/inds, and accompanied by low surface temperatures and high surface salinity, 

 at least at the locality of observation. 



In addition to an abnormally high first year of grov.'th, year class 1938 

 was marked by having scales v;hich averaged smaller than normal in relation 

 to the length of the body. 



No mtthod has yet been devised of measuring the error of scale reading 

 occasioned by the scales being irregularly marked; i.e., having too many or 

 too feviT age rings. If this error were unduly high, however, specimens as- 

 signed to a given year-class would actually be composed of several ages; 

 and if such nixing be complete, the average growth of the several year-classes 

 should be uniform. In that event, the correlations referred to above would 

 have become obliterated. The demonstration of the correlations, and their 

 persistence for three seasons is evidence that the error vras reasonably lov/, 

 we judge, for the age composition prevailing, something of the order of ten 

 percent or less.. Thus, the relatively high accuracy of age determination 

 of pilchards-'by scale reading — betvreen QO and 90 percent — and the fact that 

 results "are reproducablc by different persons, warrants the confident utiliza- 

 tion of this technique in the program of pilchard research. 



LITERATURE CITED 



Allen, Winfred Emory 



1936. Occurrence of marine plankton diatoms in a ten-year scries of 



daily catches in southern California. American Journal of Botany, 

 vol. 23 (1), pp. 60-63. 



116 



