1990 Grayling Spawning Report 



DISCUSSION 



A detailed discussion of Big Hole River grayling spawning 

 population characteristics and timing, with a comparison to results 

 from studies on other grayling populations was made in last year's 

 report (Shepard and Oswald 1989). Only information not presented 

 previously or interpreted differently from the previous report is 

 presented below. 



TIMING OF SPAWNING 



The numbers of ripe females during the 1989 spawning run 

 peaked during the period between April 26 and May 8. This 

 corresponds very closely to the period of peak spawning activity 

 (April 27 to May 10) observed during 1988 (Shepard and Oswald 

 1989). Unfortunately, during 1989 the USGS gauge at Wisdom was not 

 operated until May 1, 1989. This late start for gauge information 

 prevented us from evaluating effects of flow and water temperature 

 on grayling movement and spawning. MDFWP has alerted the USGS that 

 we need to have the gauge begin operating April 1 of each year. 



CHARACTERISTICS OF THE SPAWNING RUN 



The sex ratio of grayling identified as mature, ripe, or spent 

 was 1.6 males: 1.0 female during 1989. Sex ratios for the Big Hole 

 grayling spawning population in 1988 was 2.0 males: 1.0 females (see 

 last year's report [Shepard and Oswald 1989] for a comparison to 

 other grayling populations). 



The growth curve for grayling in the Big Hole system illus- 

 trates that the majority of growth occurs during their first two 

 years (Figure 5). The presence of some juveniles in tributaries to 

 the river and the interpretation of early growth from a few scales 

 suggests that a small segment of the juvenile population may remain 

 (rear) for up to two years in tributaries to the river. Growth of 

 fish captured during the spring of 1989 was slower than for those 

 captured during the spring of 1988. The drought of 1988 was 

 probably a major factor which contributed to this reduced fish 

 growth in the Big Hole River system. 



The relatively strong 1986 year class (age 2 fish) that was 

 seen in 1988 did not appear to carry over to 1989 which provides 

 further evidence of the stress the 1988 drought put on the grayling 

 population (Figure 4). Fortunately, it appears the grayling 

 hatched out during 1988 (1988 year class) contributed to a 

 relatively strong year class and experienced relatively high 

 survival through their first year (Figure 4). We are unsure why 



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