ated pothole areas. Drouth conditions during 

 the biennium have seriously reduced muskrat 

 populations in northeastern Montana. 



Beaver 



Beaver investigations conducted during the 

 biennium were primarily directed at keeping 

 a finger on the pulse of populations. Popula- 

 tion studies included analysis of pelt meas- 

 urements, aerial colony counts and harvest 

 analysis. 



Aerial beaver colony counts constitute an 

 index to population density and permit year 

 to year comparisons to show population trends. 

 Results of counts conducted in the fall of 1956 

 and 1957 are shown below. 



Stream 

 Miles 



Colonies 

 Counted 



Miles 

 Colonv 



1956 

 1957 



3874 

 2394 



2518 



1771 



Although nearly 70,000 beaver have been 

 taken in the last four seasons, these counts 

 show excessive densities in many areas. In 

 spite of liberal seasons, low prices simply have 

 not provided enough incentive to produce de- 

 sired harvests. 



Comprehensive harvest analysis is con- 

 ducted at the end of every season. This gives 

 the number of beaver trapped, dates of capture, 

 trapper success and ratio of private land to 

 public land trapped. 



Mink 



Analysis of catch records has shown that 

 mink have been subject to heavy trapping 

 pressure for a number of years. Since the size 

 of the mink take is influenced by market and 

 weather conditions as well as by population 

 size, information based on biological indicators 

 is used to supplement catch records as a mea- 

 sure of population condition. 



Approximately 3,300 mink carcasses were 

 collected during the biennium from cooperating 

 mink trappers throughout the state. Age and 

 sex ratios from these samples are used to re- 

 flect trends in population condition. 



Harvest age and sex ratios do not reveal 

 the actual composition of the population. For 

 this reason intensive live trapping and marking 

 of wild mink is conducted to facilitate accurate 

 evaluation of age and sex data from trapper 

 catches. 



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