LIFE HISTORY OF LAKE HERRING OF LAKE HURON 



373 



j'ear of life, and (2) that, as shown by the mcrements, the large fish of an age group 

 apparently grew more rapidly in each year of life than the small fish of that age 

 group. The second statement apparently contradicts that based on Table 41, that 

 "the smallest yearlings were the fastest growing fish and the largest yearlings the 

 slowest;" but the seeming contradiction is due to the method of grouping the data 

 of Table 42. In Table 41 the fish were grouped according to the length of the year- 

 lings, irrespective of whether these yearlings grew slowly or fast in later years. The 

 table shows that small yearlings were rapid growers and large yearlings slow growers. 

 In Table 42 the fish were grouped according to the length at death, irrespective of 

 whether they were small or large as yearlings. Because both size groups of an age 

 group of Table 42 consisted of small and large yearlings, the difference between the 

 computed lengths of the first year is consistently less than that between the actual 

 lengths of the fish at death. The table, therefore, warrants only the first statement 

 derived from it and not the contradictory second statement. 



Table 42. — Computed average length and average increment of length for each year of life for each 

 size group of various age groups of Saginaw Bay herring taken in 1922 and 192S 



Note. — The last total length value of each horizontal row is derived from direct measurements of fish. 



It appears, then, that the "law of growth compensation" holds for the lake 

 herring. We found that, on the average, the big yearlings were the big fish in all 

 succeeding years of life, but that the differences between the small and large yearlings 

 diminished each year of age — that is, the small yearlings were rapid growers, the large 

 yearlings slow growers. We also found that the "growth compensation" did not 

 overcome entirely, in their later years, the effect of unfavorable growth conditions to 

 which the Saginaw Bay herring were subjected in 1915-1918. 



NORMS OF GROWTH 



Lengths. — As suggested at the beginning of this section, in order to obtain the 

 norm of growth in a long-lived species, which is not influenced by seasonal cycles 

 of growth or annual fluctuations in it, we must combine the rates of growth for 

 corresponding ages of all year classes. Such an incomplete general norm, based on 

 direct measurements of fish, is shown near the bottom of Table 34. A complete one, 

 based on the measurements of scales, is shown at the bottom of Table 26. A third, 

 based on both uncorrected computed averages and actual averages, is shown in the 

 grand averages of Table 43. The grand averages of Tables 26, 34, and 43, both total 

 lengths and increments of length, are plotted in Figure 39. Those of Table 43 really 



