: Scientific [common] falcata [] Forest: Salmon-Challis National Forest Forest Reviewer: Bart L. Gamett Date of Review: March 30, 2018 Forest concurrence (or No recommendation if new) for inclusion of species on list of potential SCC: (Enter Yes or No)

FOREST REVIEW RESULTS:

1. The Forest concurs or recommends the species for inclusion on the list of potential SCC: Yes___ No_X_

2. Rationale for not concurring is based on (check all that apply): Species is not native to the plan area ______Species is not known to occur in the plan area ______Species persistence in the plan area is not of substantial concern ___X___

FOREST REVIEW INFORMATION:

1. Is the Species Native to the Plan Area? Yes_X__ No___

If no, provide explanation and stop assessment.

2. Is the Species Known to Occur within the Planning Area? Yes_X__ No___

If no, stop assessment.

Table 1. All Known Occurrences, Years, and Frequency within the Planning Area Location of Observations (USFS District, Town, River, Year Number of Road Intersection, HUC Observed Individuals etc.) Source of Information Salmon River 1 Near Shoup University of Michigan, Museum of Zoology, Mollusk Collection (https://fms02.lsa.umich.edu/fmi/webd/um mz_mollusks, specimen number 215976), apparent duplicate at IDFG (https://idfg.idaho.gov/species/observation/ 597638) Salmon River numerous Several locations between Vannote, R.L. and G.W. Minshall. 1982. Shoup and Corn Creek Fluvial processes and local lithology controlling abundance, structure, and composition of mussel beds. Proceedings of the National Academy of Sciences of the United States of America 79(13):4103-4107. Salmon River 60 valves Salmon River across road Philadelphia Academy of Natural Sciences from Sheepeater Shelter (http://clade.ansp.org/malacology/collection Historic Site, 5.4 miles west of s/details.php?mode=details&catalognumber Shoup =345063) , apparent duplicate at IDFG (https://idfg.idaho.gov/species/observation/ 597384) Middle Fork unknown At Boundary Creek Messner, J. Personal communication. March Salmon River 23, 2018 (Site 2) Camas Creek unknown Between Hammer Creek and Messner, J. Personal communication. March Anvil Creek 23, 2018 (Site 4) Middle Fork unknown At Boundary Creek Messner, J. Personal communication. March Salmon River 23, 2018 (Site 6) Loon Creek unknown Between Mearney Creek and Messner, J. Personal communication. March Burn Creek 23, 2018 (Site 9A) Loon Creek unknown Upstream of Burn Creek Messner, J. Personal communication. March 23, 2018 (Site 9B) Loon Creek unknown Downstream of Indian Creek Messner, J. Personal communication. March 23, 2018 (Site 9C) Camas Creek unknown Between Hammer Creek and Messner, J. Personal communication. March Anvil Creek 23, 2018 (Site 10) Middle Fork unknown Several locations between Stewart, C. Personal communication. March Salmon River Boundary Creek Launch Site 22, 2018 and Salmon River Marsh Creek unknown near bridge that crosses Matsaw, S. Personal communication. March Marsh Creek between Beaver 23, 2018 (Site 1) Creek and Capehorn Creek Elk Creek unknown at various location for several Matsaw, S. Personal communication. March miles upstream of Bear Valley 23, 2018 (Site 2) Creek Middle Fork unknown near Big Bend Camp Matsaw, S. Personal communication. March Salmon River 23, 2018 (Site 3) Middle Fork unknown camp downstream of Indian Matsaw, S. Personal communication. March Salmon River Creek airstrip 23, 2018 (Site 4) Middle Fork unknown near confluence with Marble Matsaw, S. Personal communication. March Salmon River Creek 23, 2018 (Site 5) Middle Fork unknown near confluence with Little Matsaw, S. Personal communication. March Salmon River Loon Creek 23, 2018 (Site 6) Middle Fork unknown downstream of White Creek Matsaw, S. Personal communication. March Salmon River Bridge 23, 2018 (Site 7) Middle Fork unknown near confluence with Loon Matsaw, S. Personal communication. March Salmon River Creek 23, 2018 (Site 8) Middle Fork unknown just upstream of Flying B Matsaw, S. Personal communication. March Salmon River Ranch 23, 2018 (Site 9) Middle Fork unknown near confluence with Big Matsaw, S. Personal communication. March Salmon River Creek 23, 2018 (Site 10) Salmon River numerous Several locations between Vannote, R.L. and G.W. Minshall. 1982. Shoup and Corn Creek Fluvial processes and local lithology controlling abundance, structure, and composition of mussel beds. Proceedings of the National Academy of Sciences of the United States of America 79(13):4103-4107.

a. Are all Species Occurrences Only Accidental or Transient?

Yes___ No_X__

If yes, document source for determination and stop assessment.

b. For species with known occurrences on the Forest since 1990, based on the number of observations and/or year of last observation, can the species be presumed to be established or becoming established in the plan area?

Yes_X__ No___

If no, provide explanation and stop assessment

c. For species with known occurrences on the Forest predating 1990, does the weight of evidence suggest the species still occurs in the plan area?

Yes___ No___

Provide explanation for determination

If determination is no, stop assessment

d. Map 1, Western pearlshell (Margaritifera falcata) range in Idaho (IDFG 2017a)

IDFG (Idaho Department of Fish and Game). 2017. Western pearlshell (Margaritifera falcata). Internet website: https://idfg.idaho.gov/species/taxa/20574. Accessed on December 26, 2017.

e. Map 2, Western pearlshell (Margaritifera falcata) range in (MNHP and MFWP 2017).

MNHP and MFWP (Montana Natural Heritage Program and Montana Fish, Wildlife, and Parks). 2017. Montana Field Guides – Western pearlshell (Margaritifera falcata). Internet website: http://fieldguide.mt.gov/speciesDetail.aspx?elcode=IMBIV27020. Accessed on December 26, 2017.

f. Map 3, Western pearlshell (Margaritifera falcata) distribution on the Salmon-Challis National Forest (Salmon-Challis National Forest western pearlshell GIS distribution layer queried on March 24, 2018).

3. Is There Substantial Concern for the Species’ Capability to persist Over the Long-term in the Plan Area Based on Best Available Scientific Information?

Table 2. Status summary based on existing conservation assessments

Entity Status/Rank (include definition if Other) NatureServe G5- Secure (Common; widespread and abundant) Global Rank NatureServe S2- Imperiled (At high risk of extinction due to a very restricted range, very few populations (often 20 or fewer), steep declines, State Rank or other factors) State List IDAPA- Unprotected Wildlife Status SGCN- Tier 2

USDA Forest No Region 1 Status Service No Region 4 Status

USDI FWS No records found Other No BLM status Xerces Society- Vulnerable (At moderate risk of extinction due to a restricted range, relatively few populations (often 80 or fewer), recent and widespread declines, or other factors)

Table 3. Status summary based on best available scientific information.

Species (Scientific and Common Name): Margaritifera falcata (Western pearlshell)

Criteria Rank Rationale Literature Citations 1 C Margaritifera falcata is known to occur in several streams on the See Table 1 Distribution on Salmon-Challis National Forest (see Table 1). This includes the Salmon Salmon-Challis River, Middle Fork Salmon River, Camas Creek, Loon Creek, Marsh Creek, National Forest Bear Valley Creek, and Elk Creek (see Table 1). The species may also occur in others stream on the Forest within the Salmon basin.

Confidence in Rank: High, Medium, or Low

Species (Scientific and Common Name): Margaritifera falcata (Western pearlshell)

Criteria Rank Rationale Literature Citations 2 C M. falcata is widely distributed in western North America (NatureServe Idaho Department of Fish and Distribution in 2017), although viable populations are more sparsely distributed within Game, unpublished data surrounding its range. Populations can be found in watersheds from southeast (snorkeling data available at the geographic area to central California, extending east to Utah, Wyoming, and Montana Salmon-Region Office) (NatureServe 2017). Matsaw, S. Personal In Idaho, M. falcata has been observed in many locations across the state communication. March 23, 2018 including the Coeur d’Alene, St. Joe, and St. Maries rivers in northern Idaho; the Pahsimeroi, Lost, Lower Salmon, and Little Salmon rivers and Messner, J. Personal Hells Canyon in central Idaho; and upper tributaries of the Snake River communication. March 23, 2018 and the Blackfoot River in southern Idaho (Stagliano et al. 2007). NatureServe. 2017. NatureServe M. falcata has been observed in many areas immediately adjacent to the Explorer: An online encyclopedia of Salmon-Challis National Forest including locations in the Salmon River, life [web application]. Version 7.1. Big Lost River, and Little Lost River basins (Map 1; Messner, J. Personal NatureServe, Arlington, Virginia. communication. March 23, 2018; Matsaw, S. Personal communication. Internet website: March 23, 2018; Idaho Department of Fish and Game, unpublished data). http://explorer.natureserve.org. Accessed on December 22, 2017. In summary, M. falcata is widely distributed off the Forest. Stagliano, D. M., G. M. Stephens, Confidence in Rank: High, Medium, or Low and W. R. Bosworth. 2007. Aquatic Invertebrate Species of Concern on USFS Northern Region Lands. Prepared for USDA Forest Service, Northern Region. Montana Natural Heritage Program: Helena, MT. 161 pp.

Species (Scientific and Common Name): Margaritifera falcata (Western pearlshell)

Criteria Rank Rationale Literature Citations 3 B M. falcata adults are mostly sessile (Allard et al. 2015). Mark-recapture Allard, D. J., T. A. Whitesel, S. Lohr, Dispersal studies of mature M. falcata in Merrill Creek (Oregon) found that the and M. L. Koski. 2015. Western Capability majority of mussels moved imperceptibly over the course of the study, pearlshell mussel life history in roughly one third of mussels moved 4-116 m downstream, and less than Merrill Creek, Oregon: 10% moved up to 12 m upstream (Allard et al. 2015). Mean rate of Reproductive timing, growth, and downstream movement was 0.11 m/day, but the relationship between movement. 2010 – 2014 Project distance moved and time elapsed was not significant (Allard et al. 2015). Completion Report. US Fish and Wildlife Service, Columbia River Juvenile M. falcata, called glochidia, are parasitic on salmonid fish Fisheries Program Office: species. Dispersal and recolonization of patches of M. falcata is thought Vancouver, WA. 29 pp. to be dependent on transport by host fish or water currents (Allard et al. 2015). These events are assumed to be rare, however (NatureServe NatureServe, Arlington, Virginia. 2017). For freshwater mussels in general, it is estimated that populations Internet website: separated by at least 2 km of unsuitable habitat, or 10 km of suitable http://explorer.natureserve.org. habitat, should be considered distinct populations (NatureServe 2017). Accessed on December 22, 2017.

Confidence in Rank: High, Medium, or Low 4 C M. falcata can occur at high densities in suitable habitat (Stagliano et al. Idaho Department of Fish and Abundance on the 2007; Thomas 2008). M. falcata beds found on the Selway and Salmon Game, unpublished data Salmon-Challis rivers of Idaho each had hundreds of individuals, and one population in (snorkeling data available at the National Forest Montana was estimated to contain about 1,000 individuals (Stagliano et Salmon-Region Office) al. 2007). Stagliano, D. M., G. M. Stephens, While M. falcata are known to occur in many locations across the and W. R. Bosworth. 2007. Aquatic Salmon-Challis National Forest, there is limited data regarding abundance Invertebrate Species of Concern on on the Forest. Vannote and Minshall (1982) reported M. falcata USFS Northern Region Lands. densities between 5.4 and 192 mussels/m2 on the Forest in the Salmon Prepared for USDA Forest Service, River between Shoup and Corn Creek. In 2016, snorkelers conducting Northern Region. Montana Natural fish assessments reported seeing between 10 and 100 individuals at two Heritage Program: Helena, MT. 161 sites in Loon Creek and a site in Camas Creek (Idaho Department of Fish pp.

Species (Scientific and Common Name): Margaritifera falcata (Western pearlshell)

Criteria Rank Rationale Literature Citations and Game, unpublished data). It is likely that M. falcata abundance varies considerably in the waters where it is found on the Forest. Thomas, A. C. 2008. Investigation of Western Pearlshell Mussel Confidence in Rank: High, Medium, or Low (Margaritifera falcata) Mortality in Bear Creek, King County, Washington: A Disease Ecology Approach. MS Thesis, University of Washington.

Vannote, R.L. and G.W. Minshall. 1982. Fluvial processes and local lithology controlling abundance, structure, and composition of mussel beds. Proceedings of the National Academy of Sciences of the United States of America 79(13):4103-4107.

5 D There is no population trend data for M. falcata on the Forest. M. falcata Jepsen, S., C. LaBar, and J. Zarnoch. Population Trend is thought to be in decline across its range (NatureServe 2017). Museum 2010. Margaritifera falcata (Gould, on the Salmon- specimens and the abundance of shells in Native American middens 1850) Western pearlshell : Challis National suggest that M. falcata populations were once more widespread and . The Xerces Forest abundant in some areas (Thomas 2008; Jepsen et al. 2010). Montana Society for Invertebrate populations have experienced significant declines in the past decade Conservation. Internet website: (Stagliano et al. 2007; Stagliano and Maxell 2010) and in Idaho the https://xerces.org/western- species is estimated to have declined between 37% and 50% from its pearlshell/. Accessed on December historical distribution (IDFG 2017b). While populations have declined in 22, 2017. many areas, the declines on the Forest may not be as severe since much IDFG (Idaho Department of Fish of the occupied M. falcata habitat on the Forest is within designated and Game). 2017b. Idaho State

Species (Scientific and Common Name): Margaritifera falcata (Western pearlshell)

Criteria Rank Rationale Literature Citations wilderness or in areas where potential impacts to the species are limited. Wildlife Action Plan, 2015. Boise, ID. Confidence in Rank: High, Medium, or Low NatureServe, Arlington, Virginia. Internet website: http://explorer.natureserve.org. Accessed on December 22, 2017.

Stagliano, D. M., G. M. Stephens, and W. R. Bosworth. 2007. Aquatic Invertebrate Species of Concern on USFS Northern Region Lands. Prepared for USDA Forest Service, Northern Region. Montana Natural Heritage Program: Helena, MT. 161 pp.

Stagliano, D. M., and B. A. Maxell. 2010. Aquatic Invertebrate Species of Concern: Updated Distributions, Vital Watersheds, and Predicted Sites within USFS Northern Region Lands. Prepared for USDA Forest Service, Northern Region. Montana Natural Heritage Program: Helena, MT. 55 pp.

Thomas, A. C. 2008. Investigation of Western Pearlshell Mussel (Margaritifera falcata) Mortality in

Species (Scientific and Common Name): Margaritifera falcata (Western pearlshell)

Criteria Rank Rationale Literature Citations Bear Creek, King County, Washington: A Disease Ecology Approach. MS Thesis, University of Washington. 6 C M. falcata occur in perennial, slow-moving streams from 0.5-1.5 m in Jepsen, S., C. LaBar, and J. Zarnoch. Habitat Trend on depth (Jepsen et al. 2010). Aggregations of M. falcata are associated with 2010. Margaritifera falcata (Gould, the Salmon-Challis clean, small cobbles where boulders decrease sheer stress and allow 1850) Western pearlshell Bivalvia: National Forest small gravel and sand to create a stable substrate (Vannote and Minshall Margaritiferidae. The Xerces 1982; Stone et al. 2004). M. falcata are found in areas with cold water, Society for Invertebrate high dissolved oxygen, and good water quality (Stone et al. 2004; Jepsen Conservation. Internet website: et al. 2010). While adults can tolerate silty or muddy conditions for https://xerces.org/western- unspecified amounts of time, juveniles are intolerant to sedimentation pearlshell/. Accessed on December (Thomas 2008). 22, 2017.

M. falcata habitat trends on the Forest are variable. On the Forest, 16% Stone, J., S. Barndt, and M. of areas have been assessed for changes in ground and surface water Gangloff. 2004. Spatial distribution fluctuations (USFS 2017a). Of these areas, 11% are outside the natural and habitat use of the western range of variability (NRV), and an additional 79% are trending towards pearlshell mussel (Margaritifera the NRV (USFS 2017a). Eighty-eight percent of the Forest area has been falcata) in a western Washington assessed for changes in channel and floodplain dynamics and it is stream. Journal of Freshwater estimated that 17% of the Forest is outside the NRV and 49% is trending Ecology 19(3): pp. 341-352. towards the NRV (USFS 2017a). Thomas, A. C. 2008. Investigation of For land type associations (LTAs) on the Forest with sufficient data, the Western Pearlshell Mussel Community Tolerance Quotient (CTQ) for macroinvertebrates was (Margaritifera falcata) Mortality in significantly altered in more than 76% of watersheds, and water Bear Creek, King County, temperature was significantly altered in more than 15% of watersheds Washington: A Disease Ecology (USFS 2017a). However, overall water quality is within the NRV on 41% of Approach. MS Thesis, University of the Forest, and trending towards the NRV on 34% of the Forest, in LTAs Washington. with sufficient information (USFS 2017a). In most LTAs with sufficient

Species (Scientific and Common Name): Margaritifera falcata (Western pearlshell)

Criteria Rank Rationale Literature Citations information, fine sediment values (as measured by median substrate USFS (United States Department of size) are within historic parameters (USFS 2017a). Agriculture, Forest Service). 2017a. Salmon Challis National Forest Data On a small scale, vegetation canopy cover is positively associated with M. Assessment, Riparian Ecosystems falcata distribution (Stone 2004). Along perennial streams on the Forest, Section (Draft a). approximately 22% of stream miles have improving or stable riparian vegetation, while 72% have significant departures of riparian vegetation Vannote, R. L., and G. W. Minshall. from historic conditions (USFS 2017a). 1982. Fluvial processes and local lithology controlling abundance, Much of the area currently occupied by M. falcata on the Forest is within structure, and composition of designated wilderness or other areas where potential impacts to the mussel beds. Proceedings of the species habitat are limited. In many of these areas, M. falcata habitat is National Academy of Sciences USA: likely in excellent condition. Vol. 79: pp. 4103-4107.

In summary, M. falcata habitat trends across the Forest are variable. M. falcata habitat has likely been impacted by anthropogenic activities in some areas. However, the vast amount of M. falcata habitat on the Forest is within designated wilderness or other areas where impacts to M. falcata habitat are limited. Subsequently, it is likely that high quality habitat will continue to be available for this species on the Forest into the future.

Confidence in Rank: High, Medium, or Low 7 B M. falcata habitat on the Forest could be negatively impacted by Allard, D. J., T. A. Whitesel, S. Lohr, Vulnerability of anthropogenic influences that have the potential to affect water quality, and M. L. Koski. 2015. Western Habitats on the water temperature, stream canopy cover, dissolved oxygen, pearlshell mussel life history in Salmon-Challis sedimentation, changes in streamflow, habitat connectivity, and loss or Merrill Creek, Oregon: National Forest disruption of host fish species. Anthropogenic influences that could Reproductive timing, growth, and potentially impact suitable M. falcata habitat on the Forest include movement. 2010 – 2014 Project unrestricted grazing, mining, roads, recreation, unrestricted timber Completion Report. US Fish and

Species (Scientific and Common Name): Margaritifera falcata (Western pearlshell)

Criteria Rank Rationale Literature Citations harvest, diversions, dams, and changes in climate. Wildlife Service, Columbia River Fisheries Program Office: Much of the occupied M. falcata habitat on the Forest is within Vancouver, WA. 29 pp. designated wilderness. In these areas, the potential for most anthropogenic activities to negatively impact M. falcata habitat is Behrens, P.N., R.E. Keane, D.L. limited. However, outside of designated wilderness, anthropogenic Peterson, and J.J. Ho. 2018. activities could significantly impact M. falcata habitat. Chapter 6: effects of climatic variability and change on forest Unrestricted livestock grazing in riparian areas can lead to vegetation. In Halofsky, J.E., D.L. eutrophication, which in turn can decrease dissolved oxygen content in Peterson, J.J. Ho, N.L. Little, L.A. M. falcata habitat (Jepsen et al. 2010). Increased nitrification has been Joyce, editors. 2018. Climate linked to declines of the related Margaritifera margaritifera in Europe change vulnerability and (Hovingh 2004). Headcutting can also lead to sedimentation, which adaptation in the Intermountain creates adverse conditions for juvenile M. falcata (Jepsen et al. 2010). Region. Gen. Tech. Rep. RMRS-GTR- The destruction of vegetation by grazing and trampling can also increase 374. Fort Collins, CO: US water temperatures, which would be expected to negatively affect M. Department of Agriculture, Forest falcata survival (Jepsen et al. 2010). Juvenile M. falcata, due to their Service, Rocky Mountain Research small size, appear to be particularly sensitive to water quality, and Station. breeding mussels may be especially sensitive to increased water temperatures and decreased dissolved oxygen (Wagschal and Blevins Gamett, B. 2017. An assessment of 2017). Livestock grazing has altered vegetation, water quality, and aquatic species on the Salmon- surface and groundwater fluctuations on the Forest (USFS 2017a). Since Challis National Forest in support of 1997, however, the proportion of range monitoring has shifted Forest Plan Revision. Draft 12-05- dramatically towards aquatic areas on the Forest (USFS 2016). Current 2017. levels of grazing on the Forest are presumed to be much lower than historic levels (USFS 2017b). In 2012, 78% of monitored pastures in Halofsky, J.E., D.L. Peterson, J.J. Ho, riparian areas met percent forage utilization standards (USFS 2016). N.L. Little, L.A. Joyce, editors. 2018. Climate change vulnerability and Mining, as well as agriculture and the burning of fossil fuels, can lead to adaptation in the Intermountain algal blooms that degrade water quality and ultimately decrease

Species (Scientific and Common Name): Margaritifera falcata (Western pearlshell)

Criteria Rank Rationale Literature Citations dissolved oxygen content (USFS 2017a). There are two active and Region. Gen. Tech. Rep. RMRS-GTR- numerous abandoned mining sites on the Forest (USFS 2017c). The 374. Fort Collins, CO: US Forest plans to have all abandoned mine sites in monitoring and Department of Agriculture, Forest maintenance status by 2018 (USFS 2017c). Of the 2.6 million acres on the Service, Rocky Mountain Research Forest open to the general public, approximately 1/100th of a percent is undergoing active mining. Station.

Increased sedimentation caused by roads, recreation, and the practice of Hastie, L. C., and K. A. Toy. 2008. clear-cutting can alter water quality in M. falcata habitat on the Forest Changes in density, age structure, (USFS 2017a). Polluted runoff from roads and logging waste can further and age-specific mortality in two impact water quality and temperature (Jepsen et al. 2010). Of the western pearlshell (Margaritifera roughly 4200 miles of roads on the Forest, about 66% are classified as falcata) populations in Washington unimproved (USFS 2017a). (1995-2006). Aquatic Conservation: Marine and Freshwater Since M. falcata can only disperse along stream and river corridors, Ecosystems: Vol. 18: pp. 671-678. activities that disrupt stream connectivity would also disrupt interpatch movement, as well as the movement of host fish for M. falcata glochidia. Hovingh, P. 2004. Intermountain M. falcata appears to be sensitive to changes in water quality and freshwater mollusks, USA temperature, so limited dispersal ability could negatively influence (Margaritifera, Anodonta, Gonidea, population trends under changing environmental conditions. Dams, Valvata, Ferrissia): Geography, diversions, culverts, livestock trampling, and other human alterations to conservation, and fish streamflow all have the potential to affect dispersal of M. falcata. management implications. Furthermore, M. falcata is a long-lived species, which when coupled with Monographs of the Western North low adult dispersal indicates that mature source populations would not American Naturalist: Vol. 2: Article be able to relocate if streamflow were altered. Dams are rare on the 4: pp. 109-135. Forest but there are numerous diversions on the Forest (USFS 2017a). Distribution of diversions is uneven, with the majority of diversions Howard, J. K., and K. M. Cuffey. occurring at lower elevations (USFS 2017a). 2006. Factors controlling the age structure of Margaritifera falcata in Changes in climate could also impact this species. Changes in climate are 2 northern California streams.

Species (Scientific and Common Name): Margaritifera falcata (Western pearlshell)

Criteria Rank Rationale Literature Citations expected to increase air temperatures and decrease snow to rain ratios Journal of the North American which will likely result in a smaller snowpacks, changes in stream flow Benthological Society: Vol. 25: No. patterns, and higher stream temperatures (IAP 2016). These changes 3: pp. 677-690. could negatively impact this species. Midwinter floods are also expected to become more common and increase in severity (IAP 2016). High IAP (Intermountain Adaption discharge years have been linked to significantly lower rates of Partnership). 2016. Intermountain recruitment in M. falcata mussel beds (Howard and Cuffey 2006), and M. Adaption Partnership: Climate falcata populations reach higher densities in low-flow areas. Riparian Vulnerability Assessment vegetation, which plays an important role in stream health, is predicted Summaries (Draft). to have a moderate to high vulnerability and a low to medium adaptive capacity to changes in climate (IAP 2016). Since the timing of breeding Jepsen, S., C. LaBar, and J. Zarnoch. and the release of glochidia are cued by water temperature changes 2010. Margaritifera falcata (Gould, (Allard et al. 2015), changes in riparian vegetation cover and increasing 1850) Western pearlshell Bivalvia: water temperatures would impact the timing of reproduction of M. Margaritiferidae. The Xerces falcata. Society for Invertebrate Conservation. Internet website: To project the future climate and impacts to resources in the https://xerces.org/western- Intermountain Region including the Salmon-Challis, the Intermountain pearlshell/. Accessed on December Adaptation Partnership (IAP) used Representative Concentration 22, 2017. Pathway [RCP] 4.5 and 8.5, which capture a moderate and high future warming, respectively (Halofsky et al. 2018). Although pathways Joyce, L.A. and M. Talbert. 2018. predicting lower warming exist, the 4.5 and 8.5 pathways were chosen by Chapter 3: Historical and projected the IAP because they are, in comparison, well studied providing a large climate. In Halofsky, J.E., D.L. set of projections that enhance our understanding of the possible range Peterson, J.J. Ho, N.L. Little, L.A. in future climate. Thus, this represents best available science for our Joyce, editors. 2018. Climate Forest with regard to a warming climate. change vulnerability and adaptation in the Intermountain Although uncertainty exists about the magnitude and rate of climate Region. Gen. Tech. Rep. RMRS-GTR- change (For a discussion of this see Behrens et al. 2018), warming 374. Fort Collins, CO: US temperatures are the most certain consequence of increased CO2 in the Department of Agriculture, Forest

Species (Scientific and Common Name): Margaritifera falcata (Western pearlshell)

Criteria Rank Rationale Literature Citations atmosphere. By 2100, median minimum and maximum temperature in Service, Rocky Mountain Research the Middle Rockies subregion, which includes the Salmon-Challis, is Station. projected to rise about 5-6˚F under the moderate warming scenario and about 10˚F under the high warming scenario. Regardless of scenario, the USFS (United States Forest Service) greatest departure from historical seasonal minimum temperatures Salmon-Challis National Forest. occurs in the summer. Annual precipitation projections are highly 2016. Forest plan monitoring and variable with no discernible trend under moderate warming and a slight evaluation report: Salmon-Challis increasing trend with high warming (Joyce and Talbert 2018). National Forest: Salmon and Challis Forest plans FY 2012, 2013, 2014, Most, if not all, of the activities and subsequent environmental changes and 2015. that could affect M. falcata on the Forest can also affect the persistence and activity of host fish parasitized by M. falcata (Gamett 2017). Local USFS (United States Department of extirpations and population declines of M. falcata in California, Utah, and Agriculture, Forest Service). 2017a. Washington have been linked to disruption in spawning and migration of Salmon Challis National Forest Data host fish (Hovingh 2004; Howard and Cuffey 2006; Hastie and Toy 2008). Assessment, Riparian Ecosystems In general, habitat quantity for fish species on the Forest remains Section (Draft a). unchanged from historic conditions, but habitat quality and connectivity vary greatly across the Forest (Gamett 2017). USFS (United States Department of Agriculture, Forest Service). 2017b. In summary, the vulnerability of M. falcata habitat to anthropogenic Salmon Challis National Forest Data influences varies across the Forest. Assessment, Rangeland Management and Grazing Section Confidence in Rank: High, Medium, or Low (Draft).

USFS (United States Department of Agriculture, Forest Service). 2017c. Assessment: Forest Plan Revision Renewable and Nonrenewable Energy and Mineral Resources Report (Draft).

Species (Scientific and Common Name): Margaritifera falcata (Western pearlshell)

Criteria Rank Rationale Literature Citations

Wagschal, A., and E. Blevins. 2017. Western pearlshell mussel impact assessment: Dr. Fine Bridge replacement project. State of California Department of Transportation District 1. 39 pp. 8 B M. falcata are relatively long-lived. Individuals commonly reach 30 to 40 Allard, D. J., T. A. Whitesel, S. Lohr, Life History and years of age (Howard and Cuffey 2006; Wagschal and Blevins 2017). The and M. L. Koski. 2015. Western Demographics estimated average lifespan for individuals that reach adulthood is 60-70 pearlshell mussel life history in years with some individuals exceeding 100 years (Jepsen et al. 2010; Merrill Creek, Oregon: Allard et al. 2015). However, M. falcata are unusually slow-growing even Reproductive timing, growth, and among freshwater mussel species, and based on growth rates observed movement. 2010 – 2014 Project in populations along Merrill Creek in Oregon, it could take up to 45 years Completion Report. US Fish and for an individual to reach reproductive size (>40 mm) (Allard et al. 2015). Wildlife Service, Columbia River Another study along Bear Creek in Washington estimated that mussels Fisheries Program Office: reach reproductive maturity in 9-12 years (Thomas 2008; Wagschal and Vancouver, WA. 29 pp. Blevins 2017). Adults are mostly sessile so dispersal in response to environmental disturbance is limited for the majority of the lifespan of Gamett, B. 2017. An assessment of M. falcata. aquatic species on the Salmon- Challis National Forest in support of Reproduction rates of M. falcata are highly variable between Forest Plan Revision. Draft 12-05- populations. Egg fertilization and release of glochidia typically occurs 2017. annually in the late spring and early summer (Allard et al. 2015). It is difficult to calculate the number of glochidia produced per reproductive Hastie, L. C., and K. A. Toy. 2008. mussel, but it is estimated that very large numbers of the small juveniles Changes in density, age structure, are produced, and mortality rates are also very high for very young M. and age-specific mortality in two falcata (Howard and Cuffey 2006; Allard et al. 2015). Mortality rates for western pearlshell (Margaritifera larger juveniles and adults appear to vary greatly between populations falcata) populations in Washington depending on environmental factors (Howard and Cuffey 2006; Hastie (1995-2006). Aquatic Conservation:

Species (Scientific and Common Name): Margaritifera falcata (Western pearlshell)

Criteria Rank Rationale Literature Citations and Toy 2008). Age structure studies of several populations suggest that Marine and Freshwater apparently stable populations may not be reproducing and are ultimately Ecosystems: Vol. 18: pp. 671-678. nonviable (Hastie and Toy 2008; Jepsen et al. 2010). In general, among Margaritifera spp. it is not uncommon for fewer than 67% of females to Howard, J. K., and K. M. Cuffey. reproduce, and for fertility rates to be lower than 50% (Allard et al. 2006. Factors controlling the age 2015). structure of Margaritifera falcata in 2 northern California streams. A 2009 genetic study of M. falcata found significant deficiencies in Journal of the North American heterozygosity at most loci (Jepsen et al. 2010). This could be a Benthological Society: Vol. 25: No. consequence of either genetic bottleneck resulting from declining 3: pp. 677-690. populations or hermaphroditic reproduction (Jepsen et al. 2010). Although rare instances of hermaphrodism have been documented in M. Jepsen, S., C. LaBar, and J. Zarnoch. falcata, sexual reproduction appears to be more common (Thomas 2010. Margaritifera falcata (Gould, 2008). In general, reduced heterozygosity reduces effective population 1850) Western pearlshell Bivalvia: size, decreases the ability of populations to respond to environmental Margaritiferidae. The Xerces change, and can result in genetic allee effects (Willi et al. 2005). Society for Invertebrate Conservation. Internet website: Glochidia of M. falcata are obligatory parasites of juvenile salmonids. A https://xerces.org/western- number of suitable host fish species, including brook trout (Salvelinus pearlshell/. Accessed on December fontinalis), bull trout (S. confluentus), Chinook salmon (Oncorhynchus 22, 2017. tshawytscha), cutthroat trout (O. clarki), steelhead/rainbow trout (O. mykiss), kokanee salmon (O. nerka kennerlyi), and speckled dace Thomas, A. C. 2008. Investigation of (Rhinichthys osculus robustus), occur on the Forest (Jepsen et al. 2010; Western Pearlshell Mussel Gamett 2017). Successful reproduction of M. falcata relies on the (Margaritifera falcata) Mortality in presence of and phenological synchrony with suitable host fish (Allard et Bear Creek, King County, al. 2015). M. falcata are therefore vulnerable to changes in the Washington: A Disease Ecology distribution, presence, and timing of migration and reproduction of Approach. MS Thesis, University of salmonid host species. Washington.

Despite their protective shells, M. falcata in mussel beds can be crushed Wagschal, A., and E. Blevins. 2017.

Species (Scientific and Common Name): Margaritifera falcata (Western pearlshell)

Criteria Rank Rationale Literature Citations by foot and boat traffic (Wagschal and Blevins 2017) and presumably Western pearlshell mussel impact livestock. assessment: Dr. Fine Bridge replacement project. State of A slow growth rate, variability in reproduction and survival, dependence California Department of on host fish in the juvenile stage, and low genetic diversity can all Transportation District 1. 39 pp. decrease the ability of M. falcata populations to respond to disturbances or changes in environmental conditions. Willi, Y., J. V. Buskirk, and M. Fischer. 2005. A threefold genetic In summary, while reproduction in this species is complex and can be Allee effect: Population size affects affected by numerous natural and anthropogenic influences, the high cross-compatibility, inbreeding quality and well connected habitat on the Forest will likely allow this depression, and drift load in the species to recover from natural and anthropogenic disturbances. self-incompatible Ranunculus reptans. Genetics: Vo. 169: pp. Confidence in Rank: High, Medium, or Low 2255-2265. Summary and recommendations: Margaritifera falcata (western pearlshell) is widely distributed across the Date: 03/30/2018 Salmon-Challis National Forest and is also widely distributed in areas adjacent to the Forest. The species has the ability to disperse across much of the Forest. There is limited abundance and trend data for M. falcata on the Forest but the species is likely doing well in many areas. Habitat on the Forest is in reasonably good condition and much of the habitat is within designated wilderness and is protected from many anthropogenic influences. Although reproduction in this species is complex and can be affected by numerous natural and anthropogenic influences, the presence of high quality and well connected habitat on the Forest will likely allow this species to recover from natural and anthropogenic disturbances. In summary, M. falcata is not recommended as an SCC due to its widespread distribution, limited anthropogenic threats to the species and habitats, and the abundance of high quality, connected habitat that will allow the species to recover from natural and anthropogenic disturbances.

Evaluator(s): Rei Scampavia and Bart Gamett

Forest Recommendation: This analysis indicates there is not substantial concern for the capability of Margaritifera falcata to persist over the long-term on the Salmon-Challis National Forest. Therefore, it is recommended that Margaritifera falcata not be designated as a Species of Conservation Concern.