SUMMARY 



This study focused on the distribution, relative abundance, and 

 habitat utilization of native Arctic grayling ( Thvmallus 

 arcticus) and possible dietary competition between grayling and 

 introduced brook trout (Salvelinus fontinalis ) in the Big Hole 

 River and its tributaries along a 26 mile reach of the river near 

 the town of Wisdom, Montana. The continuing decline of the Big 

 Hole River Arctic grayling population, the last remaining 

 population of fluvial grayling in the lower 48 United States, has 

 led to increasing concern and has made studies such as this 

 particularly important for the future management of this 

 population. 



Electrof ishing was used to determine the distribution and 

 relative abundance of young-of-the-year (YOY) Arctic grayling. 

 Arctic grayling, brook trout, and mountain whitefish f Prosopium 

 williamsoni ) were measured and weighed and released in the area 

 where they were captured. Stomach samples were collected from 47 

 grayling and brook trout with the gastric lavage technique. In 

 areas where large concentrations of YOY grayling were captured 

 macro- and microhabitat measurements were made to quantify the 

 grayling's preferences with respect to habitat. Three different 

 methods of electrof ishing were used to determine preferred sites 

 of grayling. The first two used a Coffelt BP-IC backpack 

 electrof isher in upstream and downstream directions in 

 'intensive-use areas' that had been previously located. The 

 third method utilized a series of stationary electrof ishing 

 grids. Microhabitat data derived through these three methods 

 were compared to determine whether the method used affected 

 capture site parameters. 



Microhabitat sites were quantified with respect to depth, 



