Quantitative data 



Island Section 



Abundance of bottom or{-;anisms 



In the summer of 19?8, work on bottom organisms was neces- 

 sarily subordinate to the fisheries investigation. As a result, the 

 total number of samples taken was small, and most of the stations are 

 represented only by single samples, .Vhile the data obtained were 

 valuable in making plans for the more detailed investigations of 1929 

 and 1930, those from the Island Section are considered too incomplete 

 to be introduced here. 



In 1929 the number of stations was reduced, but they were 

 visited at more regular intervals and more samples were taken, so that 

 the data may be considered more representative. In the Island Section 

 eight stations were established. Seven of these stations had a soft 

 mud bottom in which the Ekman dredge worked well, but at the remaining 

 one (Station 18, Pelee Island) the bottom was stony and it was im- 

 possible to take samples. Hence, the quantitative data for the Island 

 Section covers only the areas with a mud bottom. 



It is customary, at the present time, to divide lakes into 

 three zones with regard to benthic habitats: Littoral, sub-littoral, and 

 profundal. The profundal zone is, of course, not present in Western 

 Lake Erie. The dividing line between the littoral and sub-littoral 

 7.ones is usually placed at the depth vjhere rooted vegetation ceases to 

 grow, but in Western Lake Erie the shores are so exposed to v;ave action 

 that rooted vegetation is almost entirely lacking, and this criterion 

 must be abandoned. Without attempting to d efine the limits of the two 

 zones, it may be stated confidently that all of the stations studied in 

 the Island Section lie within the siib-littoral zone. The results ob- 

 tained at the seven stations studitd in 1929 are shown in Table 83. The 

 tablis shov;s, for each station, the number of samples taken, the mean 

 number of organisms per square meter, and the mean number for the seven 

 stations. Certain organisms which were very rare are not included in 

 the table. It should be remembered that the dredge covered an area of 

 LiOO square centimeters and that in converting the number per sample to 

 the number per square meter the factor 25 was used. Because of this 

 large conversion factor, too much importance should not be attached to 

 small differences in the numbers of organisms at the various stations. 



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