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FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



said to have a biological meaning. Regressions 

 of pilchard length on scale length appear to be 

 satisfactorily described by a linear equation over 

 the range of ages 1- through 5-ring (Landa 1950). 

 When the ?/-intereept differs significantly from 

 zero, the percentage error in estimated length 

 introduced by the assumption of direct pro- 

 portionality will, of course, decrease with in- 

 creasing age. 



A variety of factors renders the calculated growth 

 for the first year of life, or to the first ring on the 

 scale, only an approximation. The amount of 

 the first growth increment differs geographically, 

 which is partly explained by the northward shift 

 of spawning as the season progresses. Spawning 

 also continues for some length of time at a given 

 locality. There is consequent inequality in dura- 

 tion of the initial period of growth, so that the 

 length of the first year, from the time spawned 



until the formation of the first winter annulus, 

 depends upon the place and date of spawning. 

 The time periods represented by the /,, thus are 

 not entirely comparable with those represented 

 by other growth increments (/„). Furthermore, 

 there is least clarity in appearance of the first ring 

 on pilchard scales and greater difficulty in locating 

 it than is found with subsequent annuli, so that 

 less reliability is associated with the mean value 

 of the first growth increment, U. 



Average observed lengths at each age of all 

 the year classes sampled in the commercial catch 

 over nine seasons in five regions along the Pacific 

 coast are given in table 1. The means given for 

 each age in each region were obtained by assigning 

 equal weight to each year-class average. These 

 means were then taken as representative of a 

 mean curve of growth for each area of catch. 

 (See also Phillips 1948, p. 7.) 



Table I. — Average length of pilchard in the commercial catch of five Pacific-coast areas, by year class and age group 



See footnotes at end of table. 



