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

Abstract

Mountain Whitefish Prosopium williamsoni were historically common throughout much of the U.S. Intermountain West. However, within the last decade Mountain Whitefish have exhibited population‐level declines in some rivers. In the Madison River, Montana, anecdotal evidence indicates Mountain Whitefish abundance has declined and the population is skewed toward larger individuals, which is typically symptomatic of recruitment problems. Describing reproductive development, spawning behavior, and juvenile distribution will form a foundation for investigating mechanisms influencing recruitment. We collected otoliths and gonadal samples from fish of all size‐classes to characterize fecundity, age at maturity, and spawning periodicity. We implanted radio tags in mature Mountain Whitefish and relocated tagged fish in autumn 2012–2014. Timing of spawning was determined from spawning status of captured females and from density of eggs collected on egg mats. In spring 2014, we seined backwater and channel sites to describe age‐0 whitefish distribution. Mountain Whitefish were highly fecund (18,454 eggs/kg body weight) annual spawners, and age at 50% maturity was 2.0 years for males and 2.6 years for females. In 2013 and 2014, spawning occurred between the third week of October and first week of November. During spawning, spawning adults and collected embryos were concentrated in the downstream 26 km of the study site, a reach characterized by a complex, braided channel. This reach had the highest CPUE of age‐0 Mountain Whitefish, and the percentage of spawning adults in the 25 km upstream from a sampling site was positively associated with juvenile CPUE. Within this reach, age‐0 Mountain Whitefish were associated with silt‐laden backwater and eddy habitats. Future investigations on mechanisms influencing recruitment should be focused on the embryological phase and age‐0 fish. Received June 19, 2016; accepted March 28, 2017 Published online July 24, 2017

Myxobolus cerebralis Causes Presporogonic Mortality in Juvenile Mountain Whitefish

“…A separate experiment described in the original 2007 report (Schisler 2010) suggests that Mountain Whitefish are highly, if not completely, resistant to infection by M. cerebralis at 5 months (15,000 degree‐days), even when exposed to 10,000 actinospores per fish (Schisler 2010). In the Blackfoot and Madison rivers in Montana, Mountain Whitefish fry spawn in the fall (October and November) and hatch in the spring (February through April) (Pierce et al 2012; Boyer et al 2017). In these rivers, peak actinospore production occurs between May and July (Downing et al 2002; Pierce et al 2009) when Whitefish are 1–5 months posthatch.…”

“…They are an ecologically important forage fish for upper trophic predators, including the threatened endemic Bull Trout Salvelinus confluentus , and are a common target for anglers (Pierce et al 2012). Declines in Mountain Whitefish populations have been observed across many river systems since the 1990s, including in the Blackfoot and Madison rivers in Montana (Pierce et al 2012; Boyer et al 2017), the Big Lost and Kootenai rivers in Idaho (Elie 1997), and the main stem and tributaries of the Yampa River (Schisler 2010). The causes of these declines are not known but may relate to rising stream temperatures (Brinkman et al 2013), toxicity from mining and agricultural runoffs (Brinkman and Viera 2008; Quinn et al 2010), and stream modification (Kennedy 2009).…”

Conservation behaviour in action: using fish behaviour to understand and mitigate the impacts of hydropower development

“…Montana system, Boyer et al (2017) found no evidence that MW select for specific depths, water velocity or substrate composition at spawning sites. This was evident in the fish in my study which showed increased depth residency in winter and spring, but no depth bin preference.…”

“…Pierce et al (2012) noted a that over 30% of the adult MW showed no migratory spawning movements during the spawning season. Boyer et al (2017) also noted that a proportion of adult MW remained in close proximity to spawning grounds throughout the spawning period. As I did not directly monitor specimens to confirm spawning activity, it is also possible that MW selected these locations for foraging or overwintering purposes (Northcote 1997).…”

“…Mountain Whitefish reach and depth residency at locations within the Lower Columbia were comparable in winter-spring relative to the other seasons. The timing of MW spawning tends to be population specific, driven largely by temperature (Benjamin et al 2014) and varies according to altitude and longitude of the system (Pettit and Wallace 1975;Thompson and Davies 1976;Wydoski 2001;Boyer et al 2017). The main spawning season for MW in the Lower Columbia study system, or those close by, occurs between late October and February with a peak in January (Ford et al 1995;Irvine et al 2017).…”