Distribution and Population Status of Mussels in Eastern Montana: New Findings and Updates on Five Species East of the Divide

Scientific Disciplines
Biological Sciences - Aquatic
winged mapleleaf
quadrula quadrula
David M Stagliano Montana Natural Heritage
giant floater
mussel surveys
clams in Montana
Montana clams
mussels of Montana
Montana mussels
Volume 16, No. 4

Distribution and population status of mussels in eastern 
montana: new findings and updates on five species east of 
the divide

David M. Stagliano,  Montana Natural Heritage Program,  1515 East 6th Avenue, Helena, Montana 
59620  dstagliano@mt.gov
The first 2 yrs of the SWG state-wide mussel surveys focused on the western pearlshell, 
but we’ve also collected distributional and population data on five other mussel species 

occurring in the state, two native—fatmucket (Lampsilis siliquoidaea) and giant floater 
(Pyganodon grandis)— and three introduced species (black sandshell, mapleleaf and creek 
heelsplitter). Eastern Mussel Surveys in 2008 and 2009 focused on the Missouri, Milk, Marias 
and Yellowstone River Watersheds. Survey reaches were chosen opportunistically based on 
accessibility, previous mussel sightings and suitable mussel habitat (depositional areas and 
gravel run/glides). Aquascopes were used for shallow water transects, while SCUBA was 
utilized for deeper water (>1 m). Mussel data recorded during transects were standardized by 
time (CPUE, man-hour) and distance (mussels per 50 m). Rivers with excellent populations 
of native mussels include the Missouri River between Fort Benton and Fort Peck, the Marias 
River above Lake Elwell and within 10 mi of the confluence. In the Yellowstone River 
Watershed, the Tongue and Bighorn Rivers reported viable fatmucket populations, while catch 
rates of the fatmucket on the Yellowstone mainstem were low (avg. ~1/hr compared to ~7 /hr 
in the Missouri). We documented the first records of the giant floater in the Yellowstone Basin 
at three tributary sites (O’Fallon, Little Porcupine, Tongue River), but no evidence of this 
species in the mainstem. The introduced mapleleaf (Quadrula quadrula) has high densities 
in the Tongue River, but was not found live in the mainstem Yellowstone. Further population 
analysis and state conservation rank status will also be presented.