390 



BULLETIN OF THE BUREAU OF FISHERIES 



spawners of an age group average less in length than the spawners of that age 

 group. I found for the Oscoda herring that in the third age group 54 immature 

 individuals averaged 222 millimeters in length, while 83 mature specimens aver- 

 aged 228 millimeters, and that in the foiu'th age group 18 nonspawning fish 

 averaged 220 millimeters in length, while 131 spawners averaged 233 millimeters. 

 A priori, the Oscoda herring should then have a greater range in length but smaller 

 average lengths than the Tobico fish. Tables 55 and 56 show this to be true. In 

 the Oscoda fish the range in length is greater, but the modal and average lengths of 

 the sample as well as the average actual and computed lengths of the age groups are 

 less than in the Tobico fish. The increments of Table 56 show that these smaller 

 total lengths of the Oscoda herring ai'e due to the growth rate of either the first or second 

 year of life. The 5-year specimens of the two samples did not grow at very dift'erent 

 rates (the 6-year fish are too few in number to be considered). The nonspawners 

 were too few in number to affect the growth rates of these age groups. The 4 and 3 

 year fish of Oscoda grew less in the first year of life but as rapidly as or faster in the 

 later years of life than the corresponding age groups from Tobico. The 2-year herring, 

 which in both samples were principally immature fish, grew at the same rate in the 

 first year; in the second year the Oscoda fish grew the more slowly. 



Table 57. — Average actual and corn-puled total lengths and average computed increments of length for 

 sexually mature III and IV year herring taken in 1922 at Bay City and Oscoda, Mich.^ 



1 Tile last total lengtii value of each horizontal row is based on direct measurements of fish. 



As many more nonspawners are included in the third and fourth age groups of 

 the Oscoda sample than in those of the Bay City collection, the corresponding growth 

 rates for these age groups, shown in Table 56, are not strictly comparable. Table 57, 

 therefore, compares these rates of growth for the mature fish only. The results are 

 not radically different from those obtained above. In both age groups (Table 57) 

 the Bay City herring exceed the Oscoda fish in size. In both age groups tliis is due 

 solely to the growth rate of the first year of life. In the later years of life the Oscoda 

 herring grew faster than those from Bay City. 



The samples of herring from the other locahties on Lake Huron are too small in 

 any single year to permit of detailed comparisons. However, they may furnish some 

 information on the general gi-owth rates of the herring of these localities. To give a 

 greater number of specimens from each locality, collections made at the same locality 

 in different years are combined and treated as a unit. Table 58 shows the average 

 length in millimeters as determined by actual measurements of fish, of the individuals 

 of each of the age groups comprising the samples taken at 12 localities. Of these 12 

 localities, Bay City and Oscoda alone are adequately represented by sufficient material. 

 The Alpena, St. Ignace, Killarney, Wiarton, and possibly East Tawas samples may 

 be adequate for a comparative study of growth. Especially may this be true when 



