LIFE HISTORY OF LAKE HERRING OF LAKE HURON 403 



Suitable statistics would reveal whether or not fishing was intense in a certain 

 year. The statistics shown in Table 64, even though we assume that they represent 

 the actual quantity of fish taken each year, are not adequate to show the intensity of 

 fishing in the herring industry of Saginaw Bay. In order to determine this from the 

 data of Table 64, we must loiow the size of the herring population in the lake for the 

 year considered. A big catch in one year — as, for example, 1916 — may in reality 

 represent less intense fishing than a small catch in another year, such as 1921. If 

 in spite of this we wish to assume that a catch of a year and the growth rate of the fry 

 hatched the year following are more or less closely correlated (that is, that fry of a 

 year following one in which the catch was relatively large grow relatively fast, and 

 fry of a year following one in which the catch was relatively small grow relatively 

 slowly), we should, then, on the basis of the statistics of Table 64, expect the growth 

 of the herring fry hatched in Saginaw Bay in 1917, 1919, 1920, 1923, and 1926 to be 

 relatively large, and that of those fry hatched in 1918, 1921, 1922, 1924, and 1925 to 

 be relatively small. These expectations, however, do not agree with the fact (Table 

 39) that the fry hatched in 1917 and 1918 grew comparatively slowly while those 

 hatched in the years 1919 to 1922 grew progressively faster each year. 



It appears, then, that in all probability fishing intensity was not the controUing 

 factor in the acceleration in the rate of growth of the herring of Saginaw Bay. 



The discussion of the possible effects of temperature and fight and fishing inten- 

 sity is incomplete and inadequate because of lack of suitable data. It can not be 

 said that no correlation exists between these factors and growth rate, but that these 

 factors very hkely did not control the growth rate. It is altogether more probable 

 that a third factor was the really effective one. This third factor is the temporary 

 chemical pollution of Saginaw Bay. The history of this pollution, so far as I have 

 been able to obtain it, is given below. 



TEMPORARY CHEMICAL POLLUTION OF SAGINAW BAY AS A FACTOR 



During the World War (1915 to 1918) the Saginaw Bay fishermen received 

 many complaints relative to the odor and taste of their productSj especially perch, 

 suckers, and pickerel, taken from the bay. At the same time the city chemist of 

 Bay City, Louis P. Harrison, received similar complaints about the city water, which 

 at the time was taken from the Saginaw River. The fishery interests procured the 

 services of Dr. Herbert W. Emerson, of the University of Michigan, who, independ- 

 ently with Mr. Harrison, investigated the obnoxious poUution. By various and 

 repeated analyses of the waters of the bay and the Saginaw River system the trouble 

 was traced to the plant of the Dow Chemical Co. at Midland, Mich., about 40 miles 

 above the mouth of the river. It was discovered that the company was dumping 

 its chemical wastes directly into the river and that the objectionable taste and odor 

 of the fish and water were due to the presence of dichlorobenzol, a heavy, clear, 

 oily Hquid. 



According to Mr. Dow, the marked pollution was due to an explosion in one 

 of his chemical plants whereby a large amount of paradichlorobenzol, a useless 

 by-product at that time, was suddenly dumped into the river. 



Paradichlorobenzol (C^ H^ CI2), a white crystal, is derived from chlorobenzene 

 (Cs Hg CI), a heavy, clear Uquid, and, unlike the latter, is very soluble in water. "The 



