1990 Grayling Spawning Report 



SPAWNING RUN CHARACTERISTICS 



The sex ratio of all fish identified as mature, ripe, or 

 spent was 1.6 males: 1.0 female, but was 1.2 males: 1.0 female for 

 those fish aged (Table 2). Length and age frequency information 

 for mature fish illustrated that a large portion of the age II fish 

 were sexually mature (Table 2 and Figure 4). The fact that the 



Table 2. Mean length, length range, and sex ratio information by 

 age for the portion of the Big Hole River Arctic grayling spawning 

 run sampled during 1989. 



Age Number Mean length Length range Percent Sex ratio 

 class sampled (inches) (inches) mature (male: female) 



sex ratios change between age classes illustrates that not all 

 female grayling were maturing at age II and that female grayling 

 may be suffering higher mortality than males after age IV (Table 

 2). The average length and weight of ripe males (n = 123) was 11.8 

 inches and 0.52 pounds, respectively. The average length and 

 weight of ripe females (n = 19) was 11.4 inches and 0.48 pounds, 

 respectively. The majority of growth in length was attained at by 

 age III with the fastest growth occurring during the first and 

 second years of life (Figure 5). 



SPAWNING DISTRIBUTION WITHIN THE DRAINAGE 



Most captured grayling spawning during 1989 were found within 

 the main stem Big Hole River between the North Fork of the Big Hole 

 River upstream to approximately 3.0 miles above the Highway 43 



Page - 9 



