396 



BULLETIN OF THE BUREAU OF FISHERIES 



The only material available for the period before the year 1915 is the sample of 17 

 herring collected by Doctor Koelz in 1917 at Bay City, Mich. Doctor Koelz made no 

 effort to take unusually large herring. His only precaution was to take nothing but 

 perfect representative specimens. 



Table 60. — Actual lengths of Saginaw Bay herring captured in 1917 compared with those of herring 

 captured in 19S4 for corresponding years of life ' 



Date of capture 



Oct 25, 1917 



Nov .-Dec, 1924.. 



Actual length, in millimeters, at end of year- 



Ill 



235 (3) 



236 (162) 



IV 



246 (6) 

 243 (356) 



271 (4) 

 254 (74) 



VI 



293 (2) 

 267(18) 



311 (2) 

 280 (4) 



' The number of specimens employed is given in parentheses. 



Table 61. — Comparison, for the first 3 years of life, of average computed increments of length of herring 

 taken in 1917 with those of herring taken in 1921, 1922, 1923, and 1924- The increments of cor- 

 responding years of 1921, 1922, 1923, and 1924 fish were combined and were derived from Table 43 ' 



' The number of specimens employed is given in parentheses. 



In Table 60 the average lengths, as determined from direct measurements of fish, 

 of the herring of Koelz's sample are compared with those of the herring taken at Bay 

 City in 1924 for corresponding age groups. That is, the fish taken in 1917 are com- 

 pared with the largest taken subsequent to the year 1918. From the table it may be 

 seen that all fish taken in 1917 are longer, on the average, for their respective age 

 groups than those taken in 1924. The averages of the age groups of the 1917 sample 

 are based on too few specimens, to be sure, but their significance lies largely in the 

 fact that they are consistently larger throughout than those of 1924 for correspond- 

 ing age groups. 



In Table 61a comparison is made between the average computed increments of 

 length of the herring taken by Koelz in 1917 and those of the herring taken in 1921, 

 1922, 1923, and 1924 for the first three years of life. In order to have as large num- 

 bers of specimens in each group as possible, the computed increments of correspond- 

 ing years of life of the 1921, 1922, 1923, and 1924 fish were combined and were derived 



