debris or sludge. There is i.;ood reason to believe that conditions in 

 that section of the lake are now as favorable for Hexagenia as they 

 ever were. Absence of sludge deposits in the relatively deep parts of 

 the Island Section justified the conclusion that they were absent from 

 the wave-swept shoals and reefs, and this conclusion was confirmed as 

 far as possible, by qualitative samples taken with the bottom-sled on 

 the shallow offshore areas. Such qualitative studies revealed large 

 areas with a firm bottom composed of sand, gravel, or boulders. All 

 of the available evidence leads to the conclusion that there have been 

 no spawning grounds rendered unfit for use, and that the food relations 

 of bottom-feeding fishes have not been adversely affected. 



Bottom-feeding fishes should find conditions on mud bottom 

 particularly favorable because of the abundance of mayfly larvae. 

 Rawson (1930, pp. 125-133) found ephemerid larvae to be an important 

 item in the food of certain fishes in Lake Simcoe. Although these 

 insects made up only $.8 per cent of the bottom fauna, they formed 

 30 per cent of the food of the whitefish, and nearly one half of the 

 food of the perch and common sucker. The fact that Lake Simcoe and 

 Lake Nipigon support large numbers of bottom-feeding fishes (Rawson, 

 1930; Dymond, 1926) in spite of the small population of bottom organisms 

 (Table 123), suggests that the Island Section of Lake Erie could still 

 support as large a population of bottom-feeders as it has in the past. 



Only at the extreme west end of Western Lake Erie, near the 

 mouths of Maumee, Raisin and Detroit Rivers, was there evidence of the 

 deposition of organic debris. The areas affected are shown in Fig. 23 

 and Table 100. Aside from the presence of organic matter, the most 

 obvious difference between these areas and the Island Section, was the 

 great abundance of tubificid worms and the rarity or absence of 

 Hexagenia, Sphaeriid molluscs and chironomid larvae also were abundant, 

 but were less constant in occurrence than the tubificids. 



There arises the question of the availability of food for 

 bottom- feeding fishes in the polluted areas. The actual production of 

 living material unquestionably has increased in those areas, but the 

 Increase has taken place to a considerable extent in the tubificid 

 worms, which Richardson (1928, pp. UUIi-U53) regarded as of minor 

 importance because of inaccessibility. He believed that they would be 

 eaten in numbers only by the large bottom-feeders (carp, biiffalo, and 

 other sucker-mouthed fishes) when they took up the larger bottom or- 

 ganisms such as Sphaeriidae. If such fishes in Western Lake Erie 

 ingest large numbers of the worms along with the Sphaeriidae, it is 

 possible that they would find a larger supply of food on the polluted 

 bottonE than on the unpolluted bottoms. The carp obtains much of its 



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