"Front page"

"for : Montana Department of Fish, Wildlife and Parks"

"June 2010"

Includes bibliographical references [p. 37-41]

During the past three years, weve made significant strides toward documenting distributions and understanding Montanas freshwater mussels through data compilation, inventory and public education. Although the five eastern Montana mussel species (2 native and 3 introduced) have secure populations and are even expanding their ranges, one of the states native species, the western pearlshell, Margaritifera falcata has experienced significant range reductions in the past 100 years, and in 2008 was added to Montanas SOC list as a S2, vulnerable to extinction in the state. Despite finding eight western streams with large viable pearlshell populations (up to 3,000 mussels per km), we have evidence from hundreds of negative surveys documenting the extirpation of the western pearlshell from countless streams and hundreds of river miles throughout the state, as well as dozens of non-viable populations that will be extirpated from streams and whole watersheds (Smith River) within the next 25 years. This fact should be an impetus to continue to research and understand this species in Montana, in addition to actively pursuing restoration projects that would benefit this species or its native fish host the westslope cutthroat trout. We performed extensive surveys in most of the eastern watersheds of the state and report that the largest populations of warm water mussels, notably the native fatmucket and introduced black sandshell (avg. 8.2 and 4 mussels per hour, respectively), are found within the Wild & Scenic Missouri River between Fort Benton and Judith River landing and the Marias River (above Lake Elwell & within 10 miles of the confluence) where fatmucket populations are approaching Missouri River densities (avg. 7 per hr). The native giant floater, Pyganodon grandis is more evenly distributed and abundant in the Northern Glaciated Prairie River Basins compared to central and southeast Montana, but rarely did we find populations exceeding more than 10 mussels per hour. Our surveys in the Yellowstone River indicate that the mainstem river has much lower mussel density overall, with fatmucket catch rates averaging ~1 per hour. Although, large prairie rivers entering the Yellowstone River have higher fatmucket densities: Bighorn and Tongue Rivers averaged 6 and 5 individuals per hour, respectively. We documented the first records of live giant floaters in the Yellowstone Basin at 3 tributary sites (OFallon, Little Porcupine, Tongue River), but no evidence of this species found live in the mainstem. The introduced mapleleaf (Quadrula quadrula) has high densities in the lower Tongue River, but was not found live in the mainstem Yellowstone. The introduced creek heelsplitter have increased their upstream distribution in the Milk River system, but not to the extent that the black sandshell have expanded their range. The introduced mussels in Montana do not seem to be negatively affecting the native species, coexistence and non-exclusion is evident in stream reaches documented to have both present. But rather, they seem to be an augmentation to the mussel fauna of the state and in the case of the black sandshell seems to be more viable in the upper Missouri River than in its native sections of the Missouri River where it is in decline. Over the last three years weve given mussel survey and identification workshops to over 65 fisheries biologists and hydrologists in MT & ID to increase the knowledge base, interest and capacity to survey and report mussel populations in all regions of the state. Attendees of these workshops reported back data for an additional 100 survey reaches, including the identification of two new viable western pearlshell sites in 2009. To generate public interest and support of freshwater mussels, we produced a pocket-sized mussel field guide and a full-sized Mussels of Montana Poster which will be distributed around the state from various agency offices and within the science educational system. Increasing interest and knowledge in freshwater mussels and species other than the typical sportfish is essential for the sustainability of these species and for the concern of the health of their aquatic ecosystems

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