during periods of extreme water fluctuations. They remained stable 

 until the severe floods of 1969 and 1970 reduced their numbers. Musk- 

 rat populations made a minor recovery following the floods and have 

 remained stable. The nine-foot channel project initially benefited 

 muskrats; however, due to sedimentation and subsequent destruction of 

 aquatic and marsh plants, much of the early benefits have been lost. 



Beaver 



The beaver was once common along rivers and streams in both Illinois 

 and Missouri until the 1800' s. Their numbers gradually decreased as a 

 result of over trapping and destruction of habitat. Only a few colonies 

 remained in Missouri in 1895 (Schwartz, 1959: 165). By the late 1800' s 

 or early 1900' s beaver were exterminated in Illinois (Hoffmeister and 

 Mohr, 1972: 156). The Illinois Department of Conservation reintroduced 

 beavers in Jersey County (Illinois River Pool 26) in 1936. Several other 

 reintroductions were made in southern Illinois from 1935-1938 (Mohr, 

 1943: 533). The repppulation of the Missouri River and its tributaries 

 in north Missouri was the result of colonization by either r emn ants of 

 the original population or migrants from farther upstream (Schwartz, 1959: 

 165) . As a result of these reintroductions and movements from ad- 

 jacent areas, the beaver is now a common mammal of Pools 24, 25, and 

 26 on the Illinois and Mississippi Rivers. 



Perusal of narrative reports written by management personnel of the 

 Mark Twain Natioanl Refuge system, Calhoun and Batchtown units (Pools 

 26 and 25) indicate that beaver populations have steadily increased from 

 1949 until the mid-1960 's. The populations have remained static from 

 the mid-1960 's to the present time. 



Two possible factors responsible for the increase in beaver popu- 

 lations would be low pelt prices and increased sedimentation (Table 49 ). 

 Since the repopulation of beaver in the Illinois and Mississippi River 

 valleys, the price of beaver pelts has been low. This has resulted in 

 little trapping pressure, allowing the beaver population to grow. In- 

 creased sedimentation, which has been a result of agricultural erosion 

 and implementation of the nine-foot channel, may have been beneficial 



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