LIFE HISTORY OF LAKE HERRING OF LAKE HURON 



409 



had been exposed to the polhition during the first year of life, were 13 per cent under 

 normal weight, that the 5-year fish were 14. C per cent and the 6-year individuals 

 15.9 per cent under normal weight. These percentages represent a total loss of 

 184,450 pounds to the fishermen, or an average loss in pounds of 12.1 per cent. The 

 average price of herring in 1921, as derived from Table G4, was 3.7 cents per pound; 

 the financial loss due to the retardation in growth rate then amounted to $6,825 

 in 1921. 



The loss must have been less in 1922 than in 1921. None of the 2, 3, or 4 year 

 fish taken in 1922 had been subjected to the pollution. The 5-year individuals had 

 been exposed only during their first year of life. Computations show that they were 

 about 14.8 per cent under normal weight. The 6-year herring were 11.9 per cent 

 under normal weight. These percentages represent a total loss of 113,648 pounds to 

 the fishermen, or an average loss in pounds of 3.6 per cent, with a value (at 2.2 cents 

 per pound, Table 64) of S2,500. 



The loss must have been exceedingly small in 1923. The 6-year fish were found 

 to be about 4.5 per cent under normal weight. This represented a loss of 3,191 

 pounds, a general loss of 0.2 per cent, valued at $73. 



The data upon which the above discussion is based are summarized below : 



As the fish that composed the catches of 1915 and 1924 had been exposed only 

 slio'htly to the chemical pollution and the growth data for the fish taken in 1916 are 

 very incomplete, the losses for these years may be ignored. The averages of the length 

 of the old fish in the catches of some of the other 3'ears are likewise unavailable. 

 Those of the fish of the same age in the catch of a following year then are substituted, 

 as, due to the law of compensation in growth, the differences between the lengths of 

 the old fish of corresponding age groups of two successive year classes would be com- 

 paratively small anyhow. To illustrate the modified procedure (see p. 407) employed 

 for the years preceding 1921, the various data are given in detail for 1920 only. For 

 the other years the end results alone are given. 



Table 64 shows that in 1920 the fishermen of Saginaw Bay took 2,441,750 pounds 

 of herring, valued at $80,761. 



The fou^samples of herring taken in the years 1921 to 1924, inclusive, comprised 

 2,311 individuals, distributed among the various age groups, as follows: II, 12; III, 

 577; IV, 1,132; V, 464; VI, 109; and VII, 14. 



The computed lengths attained by the herring at various ages at the end of the 

 o'rowth year of 1920 are shown in Table 37. Those of different age groups belonging 

 to the same year class were combined into one average. These combined averages 



