GRAYLING SPAWNING REPORT 



EXECUTIVE SUMMARY 



Spawning Montana Arctic grayling (Thvmallu5 arcticus 

 montanus [Mxlner]) within the upper Big Hole River drainage were 

 sampled using electrof ishing fro.-n April through June 1988. 

 Sample sites included the main stem Big Hole River from Wise 

 River up to Jackson and the lower portions of 11 tributaries to 

 the river. Distribution of spawning grayling, habitat utili;:ed 

 for spawning, and characteristics of the spawning population were 

 described . 



Four hundred grayling were captured. The first ripe male 

 and female were captured on April 20 and April 27, respectively, 

 in the Big Hole River near the town of Wisdom. The number^ of 

 captured ripe females peaked during the period between April 29 

 and May 11 with the first spent female captured on May 4. 

 Spawning appeared to be triggered by a combination of declining 

 river flows after the initial spring sub-peak flow caused by low 

 elevation run-off and maximum daily water temperatures increasing 

 to 50 F. The sex ratio of all captured fish identified a^ 

 mature, ripe, or spent was 2.0 males: 1.0 female. A large portion 

 of age II fish were sexually mature. The average lengths and 

 weights of ripe males (n = 158) and ripe females (n = 34) were 

 10.9 inches and 0.42 pounds and 11.3 inches and 0.51 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. 



Spawning sites were characterized as 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. Mos-. 

 spawning grayling were captured in areas of hydrologic in- 

 stability. 



The age composition of the sampled population suggested that 

 the 1987 and 1985 year classes (age I and III fish, respectively) 

 were poor year classes. Conversely, the 1986 year class (age II 

 fish) was a good year class. These relative year class strengths 

 may be controlled by water flows during the first year of life. 



Of sight fish tagged during the 1988 spawning run and 

 recaptured later during the summer of 1983, two stayed in the 

 upper river near spawning areas and five moved down river oS far 

 as Divide Dam. One fish which was tagged in Deep Creek^on 

 October 29, 1987 was recaptured near Wisdom on May 4, 1988 



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