GRAYLING SPAWNING REPORT 



contained 21"'. fine mate'-ial (files, oeavarhead fwational Forest 

 Dillon, iiT) . Another- potential explanauian for this spawnirg 

 distribution is that the portion of the rx\'sr £bove the North 

 Fork may bs inherently lest stable resulv.ing if! more areas o* 

 "hydrolcgic mstabi 1 1 ty " V'ihxch creates preferred spawning 

 habitat. 



MOVEMENT 



The movement patterns observed through recaptures of tagged 

 fish and by the authors during their work on the Big Hole 

 suggests that a segment of tfie ri\erine Eiig Hole grayling 

 population spend the winter in deep pooifb in the portion of the 

 river below the l^iisdom areai as far as the Divide Dam and perhaps 

 in the lower portions of some tributaries which have deep pools 

 cr areas of groundwater recharge. During th.e spring, the 

 fiiajority of the mature grayling move up river ^nd spawn in the 

 portion of the river from the mouth of thie North Fork up to 

 immediately above Wisdom, and in the lower portions of Swamp, 

 Bteel , 3ig Lai-.e, Rock, and Sand Hollow creeks. 



During years of average and above average river flows rnost 

 of those grayling that moved up river during the spring ^emain in 

 the upper portion of the river throughout the suminer to feed 

 before ir.ovirg back down river in the fall (usually sometime 

 during October) to return to winter habitat areas. The e;.act 

 mechanism which triggers this down river movement is not known, 

 but is suspected tc be a combination of rising river flows 

 (resulting from either fall rains, increased return flows from 

 irrigation, or a combination of the two) and declining water 

 temperatures. During years of extreme low flow we have observed 

 that a large portion of the grayling which moved up river during 

 the spring migrate back down river immediately after spawning. 

 This movement pattern was observed m 1985, 1987, and 1983, all 

 years of low flow. What triggers this immediate down river 

 migration is unclear, but may be related to drastic reductions in 

 river flow during the late spring/early summer period. 



At the present time, we Are unsure if juvenile grayling 

 follow this same migration pattern in the Big Hole system. We 

 have not captured many juvenile grayling in the lower portions of 

 the Big Hole, but have frequently captured juveniles in the 

 Wisdom a,r^A. It may be that juvenile grayling m the Big f-lole 

 either r"ear up through age 11 in rhs upper portion of the 

 drainage, cr follow similar movement patterns as adults. During 

 electrof ishing sampling in the fRll of 1986, juvenile (age O) 

 grayling disappeared from the Wisdom area between the mark and 

 recapture sampling. This would support the latter of the above 

 two theories. 



Page - 27 



