Water Resources Research Act Program

Details for Project ID 2020MT123B

Student Fellowship: Reproductive and life-history traits of western pearlshell mussels in Montana

Institute: Montana
Year Established: 2020 Start Date: 2020-03-01 End Date: 2021-02-28
Total Federal Funds: $2,000 Total Non-Federal Funds: Not available

Principal Investigators: Kristen Cook

Abstract: Freshwater mussels are in the midst of a mass extinction. About 72% of mussel species in North America are extinct orimperiled compared to only 17% of mammals and 15% of birds.1 In the United States, freshwater mussels are the most endangered family of organisms.2 The western pearlshell mussel, Margaritifera falcata, was eradicated from much of its historical range in the United States.3 This species has earned conservation status in almost every state it occupies including Washington, California, Idaho, Alaska, Utah, and Montana, and is extirpated from Nevada.4Western pearlshells were extirpated from four watersheds in Montana in the 20th Century and the number of populations, and individuals, continue to decline.5 The state lost an estimated 19% of its populations (p=0.0001), and most of the populations that remain are small, isolated, geriatric, and at risk of extirpation.5 Only about 20 of ~85 pearlshell populations are expected to still be viable in Montana 100 years from now. 5 This mussel has been designated as a Species of Concern by Montana Fish, Wildlife and Parks and the Montana National Heritage Program, and a Sensitive Species by the Bureau of Land Management and the U.S. Forest Service Northern Region 1.6The decline of western pearlshells in Montana is particularly alarming considering the benefits freshwater mussels provide to aquatic ecosystems. Freshwater mussels can improve water quality through biofiltration,7 improve habitat conditions for fish,8 provide important food web components,9, 10 and act as bio-indicators.11 The western pearlshell mussel is the only freshwater mussel found in western Montana’s trout streams, and one of only three mussels native to the state.Conservation of western pearlshells in Montana will require fundamental information on reproduction and life-historytraits that is currently lacking. For example, information on the timing and duration of reproductive events is necessary to propagate western pearlshells in the future. Mussel propagation entails harvesting embryos from mussels during a specific embryo developmental stage with a narrow window of time, but the timing of western pearlshell reproduction in Montana is unknown. Reproductive timing for western pearlshells has been studied in coastal states but it varies greatly12, 13, 14 and may differ for populations in Montana due to differences in environmental temperature and temperature requirements for reproduction.15, 16 Conserving western pearlshells also requires knowledge of their host species requirements because pearlshells are obligatory parasites of salmonids during their larval life-stage. Historically, western pearlshell mussels used westslope cutthroat trout, Oncorhynchus clarki lewisi, as hosts in Montana.17 Populations of pearlshells in Montana are recruiting juveniles where westslope cutthroat trout are absent, indicating pearlshells are using another species, or several species, as hosts. However, the species they are using as hosts to complete their life cycle is unclear.