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INTRODUCTION 



The historic distribution of the Arctic grayling ( Thvmallus 

 arcticus ) in Montana included the Missouri River and its 

 tributaries above the Great Falls (Liknes 1981) . Today, the only 

 substantial stream-dwelling population in the United States 

 outside of Alaska is in the upper Big Hole River drainage. 

 Concern for the well-being of this population has increased in 

 recent years. Liknes (1981) suggested that dewatering, 

 overexploitation and interspecific competition may be factors 

 that contributed to the disappearance of the Arctic grayling from 

 most of its historic range and may be acting on the upper Big 

 Hole River population as well. The Montana Department of Fish, 

 Wildlife and Parks (MDFWP) has made spring and fall estimates of 

 the population since 1983, and over this time has seen an 

 apparent decline in relative abundance in the Wisdom area (Dick 

 Oswald and Brad Shepard, pers. comm.). 



Early in 1988, the Montana Natural Heritage Program, the 

 Montana Department of Fish, Wildlife and Parks, the Montana 

 Cooperative Fishery Research Unit, and the U.S. Forest Service 

 entered into a cooperative study of the age-specific habits and 

 habitat requirements of the Arctic grayling in the upper Big Hole 

 River drainage during the spring-summer-fall periods. This 

 report provides the results from a portion of that study, which 

 sought to obtain detailed information on the summer distribution 

 and habitat preferences of Arctic grayling in the Wisdom-Jackson 

 area, with emphasis placed on young-of-the-year fish. 



METHODS AND MATERIALS 



Selected segments of the upper Big Hole River, its 

 tributaries, and associated irrigation ditches were electrof ished 

 from July 5 to September 1, 1988 to document the distribution and 

 relative abundance of Arctic grayling. The segments were 

 assigned to "sample sections", which were discrete portions of a 

 stream, usually bordered up and downstream by non-electrof ished 

 areas, but sometimes separated from adjacent electrof ishing 

 sample sections by prominent physical features (Figure 1) . 

 Sample sections ranged in length from 0.60 to 3.49 miles, 

 gradient from 0.18 to 1.05%, and discharge from less than 1 to 

 25-30 ftVs (Table 1) . 



A two- or three-man crew worked with two mobile-electrode 

 electrof ishing systems: a Cofellt BP-IC backpack system typically 

 operated on non-pulsed direct current at 100 watts of power, and 

 a plastic flat-bottomed boat outfitted with a 240 watt 

 gasoline-powered AC generator with a Hairvey Leach rectifying unit 

 to convert current to non-pulsed or pulsed direct current. The 

 boat-mounted system was used primarily on the Big Hole River 



