B. coli and other gas -forming organisms over the 

 greater part of the eastern area and their presence 

 in such small numbers in the few positive samples 

 together with the remarkably low bacterial counts 

 at all stations, it may safely be said that sewage 

 pollution is not a limiting factor to animal life in 

 the open lake. 



There was little evidence of stagnation, even 

 in the deepest parts of the lake. Its oligotrophic 

 character is evidenced by the low bacterial counts 

 and high bottom oxygen values (73 percent satura- 

 tion in August and 72.4 percent in September). 

 These results are even more significant when the 

 lack of vertical mixing and the abundant oxygen- 

 depleting fauna in the Deep Hole are considered. 



As Entomostraca are known to feed freely on 

 some forms of bacteria, it is probable that the low 

 bacterial counts for Lake Erie, contrasted with those 

 reported from some other lakes, may be partly due 

 to the rich fauna of predatory macroplankton. 



CONCLUSIONS 



Since the object of the present survey has been 

 to determine, if possible, the cause or causes for 

 the decUne in the fishery, this aspect will be briefly 

 reviewed in light of the findings of the two seasons. 



It is a far simpler task to determine limiting 

 factors in an area known to be capable of supporting 

 a rich fish fauna in its normal condition, than to 

 attempt to determine the possibilities of an untried 

 body of water. In Lake Erie, known to have once 

 abounded with fish, it is necessary to ascertain to 

 what extent the natural requirements have been al- 

 tered by man. 



The tentative conclusions advanced at the ter- 

 mination of the first season's investigations in the 

 eastern area have been found to apply equally well 

 to the lake as a whole. 



Nothing was found to substantiate the claim that 

 the physical effecu of storms and violent cunent 

 action form a vital factor to life of any sort in the 

 region. As a matter of fact, the direct effect of 

 meteorological and physical conditions can be disre- 

 garded because they are no more severe today than 

 when the fishery was at its peak. The physical ob- 

 servations were made primarily to determine to what 



extent physical agencies might be of indirect im- 

 portance in the transportation and distribution of 

 silt and pollution. 



There is no evidence that silt from industrial 

 and sewage outwash is invading the offshore spawn- 

 ing grounds or in fact affecting any part of the area 

 investigated at distances of more than one mile from 

 the shore, except in two instances. The lake is re- 

 markably free from chemical and sewage pollution 

 and only those species spawning in or about the mouths 

 of certain streams are likely to encounter seriously 

 unfavorable conditions. 



Food apparently is present in quantities suf- 

 ficient to support a larger fish population than now 

 exists in Lake Erie. Plant and animal plankton pro- 

 duction appear to be normal and show no indication 

 of depletion. The fish have diminished but their 

 food probably has remained the same. The fact that 

 the presence of unfavorable environmental conditions 

 can often be more readily detected in these delicate 

 organisms than in the relatively more resistant verte- 

 brates offers further evidence that no environmental 

 changes of significance have taken place to date. 



The physical, chemical, and biological con- 

 ditions thus afford no explanation for the decline in the 

 fishery. It would be advisable, therefore, to examine 

 the effects of fishing upon the fish stocks. 



BIBLIOGRAPHY 



Adamstone, F. B. 



1924. The distribution and economic impor- 

 tance of the bottom fauna of Lake Nipigon. 

 Ont. Fish. Res. Lab. , Pub, No. 24, 



pp. 35-100. 

 American Public Health Association 



1925. Standard methods for examination of water 

 and sewage. 6th ed. , xi-t- 119 pp. 



Apstein, C. 



1896. Das Sdsswasserplankton. Kiel und Leipzig, 

 200 S. 

 Atkins, W.R. G. 



1926. A quantitative consideration of some factors 

 concerned in plant growth in water. Conseil 

 Internat. p. I'ExpIor. de la Mer, Jour, 

 du Conseil, vol. 1, pp. 197-226. 



Bigelow, H.B. 



1924. Plankton of the offshore waters of the Gulf 

 of Maine. Bull., U.S. Bur. Fish., 



194 



