Title

Is Whirling Disease Driving Salmonid Community Shifts in Tributaries of the Blackfoot River, Montana?

Presentation Type

Presentation

Abstract

The exotic parasite Myxobolus cerebralis, better known as whirling disease, can be lethal to certain fish species and remains a threat to salmonid populations in the United States. The parasite has had especially detrimental effects on populations in the genus Oncorhynchus (i.e. rainbow trout and westslope cutthroat trout) in some watersheds of western and central Montana, such as the Madison River and Rock Creek. Following the 1995 detection of M. cerebralis in the Blackfoot River, monitoring sites were established to measure its extent and severity in the river. Over the last two decades, Montana Fish, Wildlife and Parks has sampled the fish community in many of the same streams. Using these data we evaluated salmonid community trends in 11 streams with records of either low or high whirling disease infection levels. High infection levels have been demonstrated to have population level impacts. Previous to infection, in the late 1980s, Oncorhynchus species were dominant throughout the river, but over this time period brown trout (Salmo trutta) have become more abundant. To evaluate the potential role of whirling disease as a driver of fish community shifts in tributaries, we examined changes in community composition in streams with low to no infection levels versus high infection levels. We predicted that whirling disease resistant species such as brown trout would be the dominant species in tributaries with higher infection levels and that susceptible species (Oncorhynchus spp.) would remain the dominant species in tributaries with low infection levels. In our study, salmonid community composition changes did not appear to be strongly driven by whirling disease. Other biotic or abiotic factors are likely the primary drivers of community composition in these tributaries.

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Is Whirling Disease Driving Salmonid Community Shifts in Tributaries of the Blackfoot River, Montana?

UC 331

The exotic parasite Myxobolus cerebralis, better known as whirling disease, can be lethal to certain fish species and remains a threat to salmonid populations in the United States. The parasite has had especially detrimental effects on populations in the genus Oncorhynchus (i.e. rainbow trout and westslope cutthroat trout) in some watersheds of western and central Montana, such as the Madison River and Rock Creek. Following the 1995 detection of M. cerebralis in the Blackfoot River, monitoring sites were established to measure its extent and severity in the river. Over the last two decades, Montana Fish, Wildlife and Parks has sampled the fish community in many of the same streams. Using these data we evaluated salmonid community trends in 11 streams with records of either low or high whirling disease infection levels. High infection levels have been demonstrated to have population level impacts. Previous to infection, in the late 1980s, Oncorhynchus species were dominant throughout the river, but over this time period brown trout (Salmo trutta) have become more abundant. To evaluate the potential role of whirling disease as a driver of fish community shifts in tributaries, we examined changes in community composition in streams with low to no infection levels versus high infection levels. We predicted that whirling disease resistant species such as brown trout would be the dominant species in tributaries with higher infection levels and that susceptible species (Oncorhynchus spp.) would remain the dominant species in tributaries with low infection levels. In our study, salmonid community composition changes did not appear to be strongly driven by whirling disease. Other biotic or abiotic factors are likely the primary drivers of community composition in these tributaries.