MUSSEL FAUKA 01^ THE KAiTKAKEE BASIK". 



7 



We may be reasonably certain, therefore, that the data here ob- 

 tained are natural and authentic, and that they have not been to 

 any degree artificially modified. 



MUSSEL SURVEY. 



LOCALITIES EXAMINED. 



Station 1. The middle fork of the Yelloio River. — The entire upper 

 portion of this river, down to within 6 miles of Plymouth, has been 

 recently dredged. The result has been a conversion of the winding 

 forks of the river and their tributary streams into a series of straight 

 cross-country ditches, in which the water flows at a uniform rate 

 over an equally uniform and undifferentiated bottom of sandy gravel. 



These ditches were examined at several places (the first four sta- 

 tions) in order to ascertain what effect the dredging had upon the 

 mussels and other life in the headwaters of the river. The dredged 

 material, thrown up along the sides of the ditches, everywhere pre- 

 sented abundant evidence that mussels were formerly present in 

 considerable numbers. But the process of dredging, by throwing out 

 the living mollusks upon the land where the ditch coincided with the 

 old channel and by withdrawing the water from such portions of 

 the old channel as did not thus coincide, comfletely destroyed the 

 entire mussel fauna. There has been some restocking of the new 

 channels by ordinary natural methods, but the conditions have been 

 extremely unfavorable for such restoration. Our fresh-water Unio- 

 nidse are dependent upon small fish for their distribution and for 

 transportation into new regions like those created by this dredging. 

 At the last rebuilding of the dam at Plymouth no fishway was pro- 

 vided. Consequently, the only fish available, as well as the only 

 supply of glochidia, had to come from the short undredged space of 

 6 miles above the Plymouth dam and from such specimens as may 

 have escaped destruction during the dredging. Furthermore, the 

 reduction of the water channels to an absolutely uniform grade and 

 depth has proved very unfavorable to the spread of mussel life. The 

 constant shifting of the sand and soil along the bottom of the chan- 

 nel effectually prevents the young mussels from obtaining a stable 

 foothold anywhere. In the presence of such adverse conditions it 

 was remarkable to find any evidence of a restoration of the mussel 

 fauna. 



This first station was near the town of Bremen, in the northeastern 

 corner of Marshall County; the ditch representing the middle fork 

 of Yellow River was 6 feet wide and the water was about 8 inches 

 deep at the center. There was no vegetation of any sort present, 

 and no fish or crawfish could be found for the distance of a mile 

 above the town. The bottom of the ditch was gravel or sand, kept 



