LIFE HISTORY OF LAKE HERRING OF LAKE HURON 



389 



Table 56. — Comparison, for corresponding age groups, of computed lengths and increments in length 

 of each year of life of Bay City (Tobico) herring collected November 1, 1922, with those of Oscoda 

 herring taken November 2, 19Z2 



' The last total length of each horizontal row is based on direct measurements of flsh. 



The Oscoda sample taken in 1922, however, is fairly representative, and it is of 

 interest to compare this sample somewhat in detail with the one taken at approxi- 

 mately the same time at Bay City (Tobico). Table 55 compares the two samples 

 with respect to range in length, modal length, average length of the sample, percentage 

 abundance of each age group, percentage of males and females in each age gi'oup, and 

 percentage of immature and mature fish in each age group, while Table 56 compares 

 the computed and actual total lengths and the computed increments of length of 

 corresponding age groups of the two samples. The first striking difference between 

 the two series of herring to be noted in Table 55 is in the age composition. The 2 

 and 3 year fish (especially the former) are much better represented in the Oscoda 

 collection (5.2 and 39.5 per cent) than in the Bay City sample (0.8 and 29.5 per cent). 

 The second marked difference is in the relative abundance of males and females. 

 In every age group the males are relatively much more numerous in the Bay City 

 sample than in that from Oscoda. The males preponderate in the former collection, 

 the females in the latter. The third noticeable difference is in the percentage of 

 immature and mature fish. The percentages of immature fish in age groups II to V, 

 inclusive, in the Bay City herring are, respectively, 75, 7.4, 5.3, and 2.1 ; in the Oscoda 

 fish 94.7, 39.4, 12.3, and 4.7, respectively. In general, 5.8 per cent of all the Bay 

 City herring under consideration were nonspawning or sexually immature, while, 

 26.4 per cent of all the Oscoda fish were nonspawning. This third difference is 

 especially significant as it probably accounts for all the other differences that may exist 

 between the two samples of herring compared. 



The Oscoda sample evidently represents an earlier stage in the spawning run 

 than does the sample from Bay City, although both collections were made at approxi- 

 mately the same time. The schools of herring at Oscoda apparently had not yet 

 been as completely segregated into spawning and nonspawning fish by November 

 1 as those found at Tobico. On this basis it is to be expected that the 2 and 3 year 

 fish would be more abundant m the Oscoda collection than in the Tobico sample. 

 Most of the Oscoda nonspawning fish whose sex could be determined were females 

 (70.8 per cent). This probably explains, at least in part, why the females were 

 so preponderant in the Oscoda age groups. Computations show that the non- 



