LIFE HISTORY OF LAKE HERRING OF LAKE HURON 407 



INDIRECT ECONOMIC LOSSES IN THE HERRING FISHERIES DUE TO 

 CHEMICAL POLLUTION OF 1915 TO 1918 



The loss to the fisheries during 1915 to 1918 must have been considerable. Not 

 only did the fishermen lose through the unsalability of part of their products but 

 also through the deleterious effect of the pollution upon the growth rate of the fishes. 

 The indirect loss occasioned by the latter factor is passed by commonly as of little 

 consequence, not only by the general public but by the fishermen themselves. This 

 attitude can be accounted for by the fact that in most cases the magnitude of these 

 indirect losses must be left to the imagination or be stated in terms of description 

 instead of dollars and cents. In order, then, to stress as emphatically as possible 

 the importance of the indirect effect of pollution upon fish life and industry, I have 

 computed roughly from my growth data and herring statistics the indirect financial 

 losses suffered by the herring industry of Saginaw Bay during 1917 to 1923. 



To obtain such estimates for a certain year, I proceeded as follows: The age com- 

 position of the annual catch of the year, as shown by a representative sample, was 

 determined first. Then the average length of the individuals of each age group 

 being known, the theoretical average weight of these individuals was computed 

 by means of the length-weight formula, W=]c.U (p. 379). Next, the theoretical 

 average weight of each age group was multiplied by the number of the individuals 

 found in each corresponding age group of the sample and the total weight of the 

 whole sample ascertained. From these values the percentage, expressed in 

 terms of weight, contributed to the sample by each age group was determined. 

 Applying these percentages to the total catch of the year (Table 64), the portion of 

 the annual yield furnished by each age group was ascertained. Next, the percentage 

 under normal weight of each age group exposed to the pollution was found by com- 

 paring the theoretical weight of that age group with that of a corresponding age 

 group not exposed to the pollution. From these percentages and the total produc- 

 tion contributed by each age group to the annual catch the total number of pounds 

 under the normal was computed for each age group. The summation of these pounds 

 gave, then, the total number of pounds under the normal for the year. The multi- 

 plication of this annual total by the average price of the herring showed the monetary 

 loss for the year. 



The above process was carried out only for the herring taken in 1921, 1922, and 



1923. As no representative samples were available for the years preceding 1921, the 

 actual age composition of the catches for these years could not be determined. As 

 the age composition varies little from year to year, no good reason exists why the 

 average age composition derived from the four samples collected in the years 1921 to 



1924, inclusive, can not be employed here. The combined sample of 2,31 1 fish would 

 then serve as the standard for each year. The loss in weight, however, would still 

 be determined by the actual loss suffered during the particular year considered, as 

 shown by the uncorrected computed lengths. For some years the average weights 

 of the old fish are unavailable. In such cases the averages of fish of correspond- 

 ing ages of the following year are then employed. It is reahzed, of course, that none 

 of the calculated losses are absolutely accurate; they are rough estimates only, but 

 are far better than no estimates at all. 



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