1990 Grayling Spawning Report 



EXECUTIVE SUMMARY 



We sampled spawning Montana Arctic grayling ( Thymallus 

 arcticus montanus [Milner]) by electrof ishing within the upper Big 

 Hole River drainage from April through May 1989. Sample sites 

 included the main stem Big Hole River from above Wise River up to 

 Jackson and the lower portions of three tributaries to the river 

 were sampled from April through May. We describe the temporal and 

 spatial distribution of spawning grayling, habitat utilized for 

 spawning, and demographic characteristics of the spawning popula- 

 tion. 



We captured 407 grayling. The first ripe male was captured on 

 April 21 in Swamp Creek and the first ripe female on April 25 in 

 the Big Hole River above the Clemow Road above the town of Wisdom. 

 The numbers of captured ripe females peaked during the period 

 between April 26 and May 8 with the only spent female captured on 

 May 8. The numbers of ripe males peaked during the period between 

 April 24 and May 10. Spawning could not be correlated to river 

 flows or water temperatures because the USGS gauge did not begin 

 operating until May 1, 1989. The sex ratio of all captured fish 

 identified as mature, ripe, or spent was 1.6 males: 1.0 female. A 

 large portion of age II fish were sexually mature (61%). The 

 average lengths and weights of ripe males (n = 123) and ripe 

 females (n = 19) were 11.8 inches and 0.52 pounds and 11.4 inches 

 and 0.48 pounds, respectively. Grayling spawned primarily within 

 the main stem Big Hole River from the mouth of the North Fork Big 

 Hole River upstream to 3 miles above Wisdom, in a few scattered 

 side channels below the North Fork, and in the lower portions of 

 Swamp, Big Lake, and Rock creeks. 



We found spawning grayling on riffles with clean surface 

 gravel which appeared "bright" near pool or run habitats, generally 

 within actively degrading or aggrading side channels or alluvial 

 gravel fans at the mouth's of tributaries. We captured most 

 spawning grayling in areas of hydrologic instability where the 

 channel was actively down-cutting or depositing gravels. Measure- 

 ments in eleven areas found spawning grayling were usually captured 

 in sites where water velocities were faster and water depths deeper 

 than adjacent available areas. 



The age composition of the sampled population suggested that 

 the 1986 year class (which was a strong year class recruited to the 

 population in 1988) experienced poor survival from the spring of 

 1988 to the spring of 1989. The 1985 and 1987 year classes were 

 also poor and the 1990 spawning run will likely be a poor run. 

 Grayling hatched during 1988 made up a surprisingly good year class 

 as evident from the high numbers of age I fish captured during the 



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