POPULATION* HETEROGENEITY IN PACIFIC PILCHARD 203 



Table 1. — Average length of pilchard in the commercial catch of five Pacific-coast arras, by year class and agt group — Con. 



1 Includes samples from waters "if Washington and Oregon. 

 •Less than 10 fish sampled. 



TRANSFORMATION OF GROWTH CURVES 



When such growth curves of means-of-average 

 observed lengths for each area are transformed, 

 using Wal ford's (1946 a) plot of/,,,, on /„, Ggure 1 

 results. These transformations show marked 

 deviation from the linearity characteristic of this 

 plot for more homogeneous groups of lish (or of 

 other animals). They are illustrative, however, 

 of growth characteristics of different areas. As 

 defined by Walford, these are (I) the slope of the 

 regression, /,', representing the rale of deceleration 

 of growth; and (2) the predicted ultimate size, 

 (/-intercept 



and San Francisco show growth characteristics 

 intermediate between those of catches landed 

 in the south at San Pedro and in the Pacific 

 Northwest off Oregon, Washington, and British 

 Columbia. 



Growth data on European pilchard (Sardina 

 pilchardus) assembled from various sources by De 

 Buen (1937) are plotted similarly (as trans- 

 formations) in figure 2 for different geographical 



Pilchard landed at Monterey 



areas. These curves are based on back calcula- 

 tions of length obtained for the most part by the 

 direct-proportion formula. Differing growth 

 types, possibly representing dines (or gradients) 

 of growth, are indicated from north to south, 

 extending from waters off England through the 

 southern European Atlantic to the Mediterranean. 

 In figure 2, solid symbols represent transforma- 

 tions of grow tb curses of pilchard off Cornwall, 

 Plymouth, and Northumberland; various crosses 

 and parts of crosses show growth transformations 

 of pilchard from the English ( Jhannel off Boulogne, 

 from other waters south along the French and 

 Spanish coasts as far as Cadiz and the Azores; 

 and open symbols represent pilchard growth 

 types from the Mediterranean. As early as L913 

 Page suggested, on the evidence of growth, that 

 two distinct races of sardines exist, one in the 

 Atlantic and another in the Mediterranean. He 

 also noted (1920) that the relative dwarfism of 

 Mediterranean races is not peculiar to the sardine, 

 but has also been noticed in the anchovy and other 

 species common to the two seas. 



