Spawning Behavior and Juvenile Distribution of Mountain Whitefish in the Madison River, Montana

Mountain Whitefish were historically common throughout much of the Intermountain West.  However, within the last decade Mountain Whitefish have declined in some rivers.  In the Madison River, Montana, anecdotal evidence indicates abundance has declined and the population is skewed toward larger individuals, which is typically symptomatic of recruitment problems.  Describing spawning behavior and juvenile distribution will form a foundation for investigating mechanisms influencing recruitment.  We relocated mature radio-tagged Mountain Whitefish in autumn 2012 - 2014.  Timing of spawning was determined from spawning status of captured females and eggs collected on egg mats.  In spring 2014, we seined backwater and channel sites to describe age-0 distribution.  In 2013 and 2014, spawning occurred between the third week of October and first week of November.  During spawning, 28% of tagged fish were observed in an area accounting for 5% of study site length.  The reach downstream of this area yielded the highest C/f of age-0 Mountain Whitefish, and the percentage of spawning adults in the 25 km upstream of a sampling site was positively associated with age-0 C/f .  Within this reach, age-0 Mountain Whitefish were associated with silt-laden habitats.  Future investigations on mechanisms influencing recruitment should be focused in these areas.