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SUMMARY 



This report documents investigations of the distribution, 

 relative abundance and habitat utilization of Arctic grayling 

 ( Thymallus arcticus) and other fishes in selected segments of the 

 upper Big Hole River, its tributaries and associated irrigation 

 ditches from 5 miles north of Wisdom upstream to 7 miles south of 

 Jackson during the period July 5 to September 8, 1988. 



Electrof ishing was used to document the distribution and 

 relative abundance of fishes. Greatest concentrations of 

 young-of-the-year (YOY) Arctic grayling were found in Swamp 

 Creek, the west channel of the Big Hole River above and below the 

 Wisdom bridge (including an irrigation ditch above the Wisdom 

 bridge) and the east channel of the Big Hole River below the 

 Wisdom bridge. Older grayling followed this same pattern of 

 occurrence, with three notable differences: 1) seven age 1+ fish 

 (<9 inches) were found in Governor Creek; 2) no older fish were 

 found in Swamp Creek; and 3) no older fish were found in the 

 irrigation ditches. 



Young-of-the-year brook trout ( Salvelinus fontinalis ) were 

 plentiful in two of the three upper sample sections (Nelson Lane 

 and Dick Hirschy Ranch), the tributaries (Steel, Swamp and 

 Governor Creeks) and the east channel of the Big Hole River below 

 the Wisdom bridge. They were scarce in all other sample sections 

 around the Wisdom Bridge and absent in the irrigation ditches. 

 Older brook trout followed this same general pattern, except that 

 older fish were plentiful in the uppermost sample section 

 (Dooling Bridge) . 



Rainbow trout ( Oncorhynchus my kiss ) were plentiful only in 

 the uppermost sample section and in Governor Creek. Only nine 

 rainbow trout were found in lower sample sections of the 

 drainage, and may have drifted down from upper portions of the 

 drainage. 



Other fish species captured in the Study Area were white ^ 

 sucker ( Catostomus commersoni ) , longnose sucker ( Catostomus 

 platyrhynchus ) , mottled sculpin (Cottus bairdi ) , burbot ( Lota 

 lota ) , mountain whitef ish ( Prosopium williamsoni ) , and longnose 

 dace ( Rhinichthys cataractae ) . 



Mean total length (+ SD) of young-of-the-year Arctic 

 grayling increased from 2.45 ± 0.12 inches to 4.26 + 0.37 inches 

 between July 7 and September 1. These fish were considerably 

 longer than those measured by Liknes (1981) in 1979 at the same 

 time of year and location; the reason for this may be related to 

 higher water temperatures in 1988 than in 1979. 



Length-frequency distribution of Arctic grayling over 6 

 inches was bimodal, with peaks at 7.0-8.5 inches and 9.0-11.0 



