TheSG thrive curves arp closely simil.-ir. In all tnroe, the first year's 

 grov/th increment for year classes 1933, 1937, and 1938 deviates above the 

 norm. In six out of seven points all throe curves are in agre-ement. The 

 probabilitj'- that such agreement could occur by chance is slight. i/ In the 

 absence of random occurrence, then, the agreement must mean that specimi'^ns 

 having certain growth characteristics in common were allocated consistently 

 to the same year classes tliree years in succession. It remains to be shown 

 iThether the allocation vfas correct. 



EFFECT OF ENVIROMLIEOT ON THE GRa'/TH 0? THE PILCHARD, 

 AND ITS BE.IRING ON AGE DETER!IINATION 



If the anomalies described in the preceding section are a characteristic 

 of the year classes, they must reflect some varying environmental condition 

 that influences grovrbh of body and scales. The most obvious- such element 

 is temperature. Surface temperatures of the sea at several points along the 

 coast have been compiled by the Scripps Institution of Oceanography, and have 

 kindly been made available for this study by the Director, Dr. H. U. Sverdrup. 



Mean temperatures, at these points, for calendar years and for various 

 combinations of months for years 1932 to 193B inclusive, were averaged, and 

 deviations computed in the same v;ay as had been done with the growth incre- 

 ments. In all combinations of months tried, the deviations from the norm 

 are negatively correlated with the anomalies in the. calculated first year's 

 growth. The means of temperatures measured at Scripps Institution Pier for 

 the period June to August, however, had a higher negative correlation than 

 those for other localities and other combinations of months; and deviations 

 from their norm are shown inverted as the fifth curve of the Series in fig- 

 ure 6. The months represented are those in which growth of young pilchards 

 is most rapid (cf. lui'alford and Mosher, 19U3). 



Of more fundamental influence than the temperature on the marine environ- 

 ment, hooce on biology of the pilchard, is wind. For it is .the northvrest 

 winds prevailing along the California coast during spring arid summer that 

 produce the phenomenon of upwelling. This results in the transport of nu- 

 trients to the surface v;aters, making them available to the plankton organ- 

 isms » Thus, Tiltimately, it results in the production of food which the pil- 

 chard eats .3,/ 



i/ The deviations given in the data collected in 1939-UO (top curve o:f fig. 6) 

 are correlated with those corresponding in the data collected in 19iiO-Iil 

 (second curve of fig. 6), with an r of .93 J and P of less than .01, according 

 to Fisher's t test. "" 



_/ Temperature data were studied for the following localities: Scripps In- 

 stitution Pier at La Jolla, Lat, 32° ^2' N.j the Pier at Balboa, Lat. 33° 36' Nf 

 Huenemo, Lat. 3U° 9' N.; Pacific Grove, Lat. 36° 33' N.; North Farallon Is- 

 land, Lat. 37° U2» N.J Blunt «s Reef, Lat. U0° 2?' N. 



3/ 



- For a discussion of the relation between wind and the circulation along 



the Pacific coast, see Sverdrup, 1938.2, 1938.3; Sverdrup and Allen, 1939. 



112 



