Ron. Pierce

Correlation of Fluvial Rainbow Trout Spawning Life History with Severity of Infection by Myxobolus cerebralis in the Blackfoot River Basin, Montana

Abstract To assess the exposure of Blackfoot River rainbow trout Oncorhynchus mykiss to the exotic parasite Myxobolus cerebralis, the causal agent of whirling disease, we investigated the spawning life histories of adult rainbow trout with respect to the distribution and severity of infection in spawning and early rearing areas in two distinct reaches of the Blackfoot River. Radiotelemetry confirmed that Blackfoot River rainbow trout express a fluvial life history and migrate from wintering sites within the Blackfoot River to spawning sites in the lower reaches of tributaries. Spawning peaked in late April, and fry emergence was estimated to occur within a narrow window of time in early July during the known period of high parasite exposure. However, the severity of infection varied between study reaches. Spawning of lower Blackfoot River rainbow trout was dispersed among the lowermost reaches of smaller, colder, higher-gradient tributaries, most of which fell below our ability to detect infection. By con...

Instream habitat restoration and stream temperature reduction in a whirling disease-positive Spring Creek in the Blackfoot River Basin, Montana

AbstractAnthropogenic warming of stream temperature and the presence of exotic diseases such as whirling disease are both contemporary threats to coldwater salmonids across western North America. We examined stream temperature reduction over a 15-year prerestoration and postrestoration period and the severity of Myxobolus cerebralis infection (agent of whirling disease) over a 7-year prerestoration and postrestoration period in Kleinschmidt Creek, a fully reconstructed spring creek in the Blackfoot River basin of western Montana. Stream restoration increased channel length by 36% and reduced the wetted surface area by 69% by narrowing and renaturalizing the channel. Following channel restoration, average maximum daily summer stream temperatures decreased from 15.7°C to 12.5°C, average daily temperature decreased from 11.2°C to 10.0°C, and the range of daily temperatures narrowed by 3.3°C. Despite large changes in channel morphology and reductions in summer stream temperature, the prevalence and severity o...

Spawning Behavior of Mountain Whitefish and Co-occurrence of Myxobolus cerebralis in the Blackfoot River Basin, Montana

Abstract To assess the exposure of Blackfoot River mountain whitefish Prosopium williamsoni to the exotic parasite Myxobolus cerebralis, the cause of salmonid whirling disease, we investigated the spawning behavior of 49 adult mountain whitefish and their overlap with M. cerebralis within the Blackfoot River basin, Montana. A majority of the mountain whitefish radio-tagged in the Blackfoot River migrated upstream (range, 0.1–79.0 km) to spawning sites located primarily in the main stem of the Blackfoot River. Spawning ranged from 31 October in the lower river to 9 November in the upper river and occurred across a range of substrate and channel types. Despite later spawning in the upper river, eggs hatched earlier under the warming influence of groundwater inflows. Here, a majority of wild mountain whitefish fry (65%) tested positive for M. cerebralis infection during the immediate posthatch period of mid-April. Conversely, mountain whitefish fry from the lower river, downstream of the groundwater influenc...

Does Whirling Disease Mediate Hybridization between a Native and Nonnative Trout

AbstractThe spread of nonnative species over the last century has profoundly altered freshwater ecosystems, resulting in novel species assemblages. Interactions between nonnative species may alter their impacts on native species, yet few studies have addressed multispecies interactions. The spread of whirling disease, caused by the nonnative parasite Myxobolus cerebralis, has generated declines in wild trout populations across western North America. Westslope Cutthroat Trout Oncorhynchus clarkii lewisi in the northern Rocky Mountains are threatened by hybridization with introduced Rainbow Trout O. mykiss. Rainbow Trout are more susceptible to whirling disease than Cutthroat Trout and may be more vulnerable due to differences in spawning location. We hypothesized that the presence of whirling disease in a stream would (1) reduce levels of introgressive hybridization at the site scale and (2) limit the size of the hybrid zone at the whole-stream scale. We measured levels of introgression and the spatial ext...

Associations of Channel Form with Spawning Riffle Quality and Macroinvertebrate Assemblages in Small Restored Spring Creeks of Western Montana

Abstract Spring creeks are highly prone to degradation from anthropogenic (e.g., grazing-related) sediment, yet little is known to guide sediment reduction through restoration. This long-term study explored associations of basic channel form with riffle substrates and trout spawning site quality, along with nine macroinvertebrate taxa groups and two biotic indices in four actively restored (reconstructed with > 10 years rest from livestock grazing) and four unrestored (damaged by land use, including riparian livestock grazing) spring creeks in western Montana. Despite no change in channel slope, riffles in restored streams had lower width-to-depth ratios (10.2 ± 1.8 versus 19.2 ± 4.6), higher velocities (0.71 ± 0.18 versus 0.39 ± 0.09 m/s), lower percentage of sediment < 6.3 mm (25.9 ± 6.6 versus 41.4 ± 6.2) and higher quality spawning sites than unrestored streams. These results suggest stream restoration can improve spawning substrate by facilitating sediment transport via reduced width-to-depth ratio. When all streams were considered, the richness of sediment-tolerant macroinvertebrates were inversely correlated with riffle substrate size; whereas, clinger (sediment-intolerant) richness correlated positively with riffle substrate size. Of the two biotic indices, the Montana Mountains and Foothills Biotic Index showed no correlation to the nine taxa groups. Whereas, a significant correlation of the Fine Sediment Biotic Index with sediment < 6.35 mm suggests it may be a better indicator of spring creek habitat integrity and restoration effectiveness.