LIFE HISTORY OF LAKE HERRING OF LAKE HURON 



385 



ture herring in the third and older age groups is greater than that suggested in Table 

 50 seems substantiated by the data of the Oscoda herring, page 388, Table 55. The 

 percentages of immature fish, especially for age Groups III and IV, are considerably 

 larger in the Oscoda sample than in any of the samples taken at Bay City. The 

 Oscoda herring apparently had not yet been completely segregated into spawning 

 and nonspawning fish.) To obtain accurate values for the relative abundance of 

 sexually immature and mature fish of the general population in an age group we must 

 determine the component year classes and age groups of schools of immature fish and 

 follow them for several consecutive years. 



COMPARISON OF SAMPLES OF HERRING TAKEN IN 1924 AT THE SAME LOCALITY IN 

 SAGINAW BAY BUT ON DIFFERENT DATES 



In Tables 51 and 52 the individual herring samples of a single locality in Sag- 

 inaw Bay are compared, one with the other, in order to ascertain if possible whether 

 the characteristics of a sample vary in any one direction with the advance of the 

 season; that is, to determine whether samples taken on different dates are compar- 

 able. In Table 51 the range in length, the modal length, the average length of the 

 sample, the average actual length of each age group, and the relative abundance of 

 each age group are compared; in Table 52 the computed lengths for each year of life 

 of corresponding age groups are compared. The Tobico samples show virtually no 

 differences in the range in length or the average size of the sample, and while the 

 actual and the computed lengths of the age groups and the percentages of abundance 

 vary with the samples, these variations are not consistent. The range in length and 

 the age composition are virtually the same in the two Nayanquing samples. The 

 herring taken on November 27 tend to average somewhat less in length than those 

 taken on November 24, although the computed growth rates of the two series of 

 fish are virtually identical (Table 52). In the two Gravelly Point samples the age 

 composition is very similar; the range in length is considerably less in the herring 

 taken December 4 than in those taken November 30. The modal length and the 

 average size of the former fish exceed those of the latter. This, however, is due en- 

 tirely to the small 3-year fish taken on November 30. The growth rates of the 4 

 and 5 year fish are virtually identical for corresponding years of life. 



Table 51. — Range in length, modal length, average length of sample, average actual length of each age 

 group, and percentage of abundance of each age group for each individual sample of herring taken 

 in 1924 on different dates at Tobico, Nayanquing, and Gravelly Point in Saginaw Bay ' 



1 The number of specimens employed is shown in parentheses. 



' The mode could not be determined for the Tobico samples as in each sample two or three size classes included the greatest 

 number of individuals. 



