Comparing the station at the range lights (252) with the 

 one at the entrance to Toledo Harbor (25ii), we find a change in 

 relationship. With increased distance Diaptomus decreased rather 

 than increased in abundance. However, the decrease in Cyclops and 

 nauplii continued. There was little difference in the numbers of 

 Cladocera. The three stations can be compared more conveniently in 

 the last three columns of Table 76, which show the average counts 

 for five common dates in 1930, Diaptomus was so rare in 1930 that 

 little reliance can be placed in the figures, but it is interesting 

 to note that the highest average was recorded again for Station 252. 

 Cyclops was equally abundant at the two inner stations but declined 

 at the outer one. The nauplii showed a marked decrease as distance 

 from the river increased, thus agreeing with the data of 1929. 

 Daphnia was again most abundant at the middle station,, Diaphanosoma 

 was rare at all three stations, but showed a slight increase with in- 

 creased distance from the river. The rotifers were very abundant near 

 the river and dropped off markedly at the two outer stations. 



The most striking feature of these data is the consistent 

 and marked decrease in abundance of the nauplii and rotifers as one 

 progresses from the river's mouth out into the lake. This finding 

 is in accordance with expectation, for the plankton algae, upon which 

 they feed in part, declined witu greater distance from the river. 

 In 1929 rotifers were not counted, but the nauplii decreased much 

 as they did in 1930. The reason for the failure of the adult Crustacea 

 to decrease in the same way is not evident. The adults as a group were 

 most abundant at Station 252 in both years, but there were notable 

 exceptions among the individual genera. 



In later pages the abundance of Crustacea in this section of 

 the lake will be compared with that of other sections. 



River Raisin Section 



Samples were taken only at Station 117 in the River Raisin 

 Section. Five senes were taken in 1929, and seven series in 

 1930 (Table 77). The data show clearly that Diaptomus was much more 

 abundant in 1929 than in 1930, and that Cyclops was more abundant in 

 1930 than in 1929. Similar differences were noted in the Island 

 Section. For comparable periods, the nauplii were about equally 

 abundant in the two years, while Daphnia and Diaphanosoma were most 

 abundant in 1930. The data of 1929 are too scattered to show any 

 seasonal trends. In 1930, as far as comparisons can be made, the 

 seasonal trends were similar to those in the Island Section for 



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