The dwarf wedgemussel Alasmidonta heterodon is a federally endangered freshwater mussel species inhabiting several Atlantic Slope rivers. Studies on population demographics of this species are necessary for status assessment and directing recovery efforts. We conducted qualitative and quantitative surveys for dwarf wedgemussel in the mainstem Delaware River and in four of its tributaries (Big Flat Brook, Little Flat Brook, Neversink River, and Paulinskill River). We quantified population range, relative abundance, size, size structure, and sex ratio within each river. We estimated total dwarf wedgemussel population size for the surveyed rivers in the Delaware Basin to be 14,432 individuals (90% confidence limits, 7,961–26,161). Our results suggest that the historically robust Neversink River population has declined, but that this population persists and substantial populations remain in other tributaries. Sex ratios were generally female-biased, and small individuals (<10 mm) found in all rivers indicate recent recruitment. We most often found dwarf wedgemussel at the surface of the sediment (not buried below) in shallow quadrats (<2.00 m) comprised of small substrate (sand in tributaries; cobble in the mainstem) and minimal aquatic macrophytes. Long-term monitoring, continued surveys for new populations, and assessments of reproductive success are needed to further understand dwarf wedgemussel viability within the Delaware River basin.

Freshwater mussels (Bivalvia: Unionidae) are one of the most critically imperiled faunas worldwide and are threatened by a variety of anthropogenic stressors including impoundments, invasive species, pollution, and habitat degradation (Lydeard et al. 2004; Strayer et al. 2004). Nearly 67% of North American species have been listed by the Natural Heritage Network as vulnerable, imperiled, or extinct since their status was last reviewed nearly a decade ago (Lydeard et al. 2004). Management agencies have made freshwater mussel conservation and restoration a priority (National Native Mussel Conservation Committee 1998); however, successful conservation and restoration depends on estimates of population size and viability for both common and rare species. These data require repeated monitoring through time, often across large spatial scales.

The dwarf wedgemussel Alasmidonta heterodon inhabits rivers along the Atlantic coast (USFWS 1990) and was listed as a federally endangered species in 1990 pursuant to the US Endangered Species Act (ESA 1973, as amended; USFWS 1990, 1993). It is a small (typically <38 mm), sexually dimorphic species that generally resides in stable fine particulate (sand and gravel) substrates (USFWS 1990; Strayer and Ralley 1993; Michaelson and Neves 1995; Strayer et al. 1996). Historically, populations of dwarf wedgemussel existed in at least 70 locations extending from North Carolina north to New Brunswick in 15 different Atlantic Slope drainages (Strayer et al. 1996). At the time of listing as endangered in 1990, populations were believed to persist in 10 to 20 of the 70 historical locations and in 5 to 8 of the historical drainages ranging between the Petitcodiac River, Canada, south to the Neuse River, North Carolina (USFWS 1993).

Strayer et al. (1996) completed a range-wide assessment of dwarf wedgemussel populations between North Carolina and New Hampshire and found the least vulnerable populations residing within the Connecticut River (New Hampshire/Vermont), the Ashuelot River (New Hampshire), the Neversink River (New York), the Po River (Virginia), and Shelton Creek/Tar River (North Carolina). However, low densities, small ranges, and population patchiness was exhibited by all populations and are factors that increase the probability of local extinction. Like other freshwater mussel species, dwarf wedgemussel larvae (glochidia) are obligate ectoparasites on one or more host fish species. Laboratory-identified hosts include the tessellated darter Etheostoma olmstedi, johnny darter Etheostoma nigrum, slimy sculpin Cottus cognatus, mottled sculpin Cottus bairdi, striped bass Morone saxatilis, and Atlantic salmon Salmo salar (Michaelson and Neves 1995; Wicklow 2004; St. John White 2007). However, researchers have observed dwarf wedgemussel glochidia only on tessellated darters in the field (McLain and Ross 2005; St. John White 2007). Reliance on this nonvagile host fish species may limit dwarf wedgemussel dispersal, another factor affecting its extinction risk (Lee et al. 1998; McLain and Ross 2005).

According to the U.S. Fish and Wildlife Service (USFWS) recovery plan (USFWS 1993, 2007), at least 13 populations of dwarf wedgemussel must be shown to be viable (i.e., large populations with sufficient genetic variability and annual recruitment to be considered self-sustaining) in order to upgrade the status of the species to threatened (ESA 1973). This criterion has been partially met in the Connecticut and Ashuelot rivers, but population trends in other parts of dwarf wedgemussel's range have yet to be assessed (USFWS 2007). To remove this species from the endangered species list (ESA 1973) entirely, populations must be broadly distributed and protected from anthropogenic and natural threats (USFWS 1993, 2007). Therefore, population status assessments, identification of new populations, and long-term monitoring data are necessary for a change in status. Such information allows managers to focus efforts on populations with the highest recovery potential.

The Delaware River basin (drainage area ∼17,500 km2) was documented by Strayer et al. (1996) to support one of the largest remaining populations of dwarf wedgemussel (>10,000 animals) within one of its major tributaries, the Neversink River. Researchers discovered new populations of this species in the Paulinskill River in 1998 (J. Bowers-Altman, New Jersey Division of Fish and Wildlife, personal communication), and in the mainstem Delaware River and two additional tributaries (Big Flat Brook and Little Flat Brook) in the early 2000s (W.A. Lellis, U.S. Geological Survey, unpublished data); however, population estimates were not available at the time of status review (USFWS 2007). Additionally, severe flood events occurred throughout the entire Delaware Basin in 2005, which may have impacted existing dwarf wedgemussel populations (Cole and St. John White 2006; Suro and Firda 2006). In this study, we conducted surveys between 2000 and 2009 to assess freshwater mussel populations throughout the Delaware River basin. We assessed population trends of known dwarf wedgemussel populations, identified and established abundance estimates for newly documented populations, quantified key demographic characteristics of each population (size structure, sex ratio), and characterized microhabitat use throughout the Upper Delaware River basin. We discuss findings in light of historical population estimates for the region and provide critical data for future status assessments for this species.

Study location and design

We completed mussel surveys throughout the Delaware River basin as part of an inventory and monitoring effort for the National Park Service to document distribution, abundance, and species richness of freshwater mussels in the basin. Surveyed streams included the mainstem Delaware River, Big Flat Brook, Little Flat Brook, the Neversink River, the Paulinskill River, the Bush Kill River, Brodhead Creek, Marshalls Creek, Shawnee Creek, and Vancampens Brook. The focus of this paper is only on streams where we found dwarf wedgemussel during the Delaware Basin inventory: the upper and middle reaches of the mainstem Delaware River and its four tributaries including Big Flat Brook (drainage area ∼130 km2), Little Flat Brook (drainage area ∼40 km2), the Neversink River (drainage area ∼900 km2), and the Paulinskill River (drainage area ∼450 km2; Figure 1).

We completed qualitative and quantitative surveys (see below) over an approximately 9-y period (Table 1) as part of the efforts to survey mussel populations throughout the watershed. We completed mussel surveys in summer using a two-phase approach in which we completed continuous qualitative surveys over a large stretch of river (Table 1). We divided each river into approximately 200-m contiguous sections and each section was visually searched by 5 to 8 observers (depending on river size) using snorkel gear. We measured the reaches by targeting an object approximately 200 m downstream with range-finding binoculars; in some instances, we used nearby landmarks (bridges, boat launches, etc.) to provide additional points of reference for later GIS verification of survey distances.

We conducted quantitative surveys in a subset of sections after qualitative surveys were completed, except in the Paulinskill River. The number of sections that we chose for quantitative surveys varied according to river, resource availability, and amount of effort needed to generate accurate and precise population estimates. In the Delaware River mainstem and Little Flat Brook, we quantitatively surveyed all sites where we had identified dwarf wedgemussels in qualitative surveys. We also surveyed adjacent upstream and downstream sections where conditions were suitable for deploying quadrats. We did not survey adjacent sections if they were composed primarily of rapids or deep pools inaccessible to snorkelers.

We used an alternate study design in Big Flat Brook and the Neversink River, where dwarf wedgemussel distributions were more extensive and catch per unit effort (CPUE) varied significantly across qualitatively surveyed areas. In these rivers, we classified sections into dwarf wedgemussel CPUE categories (Neversink River: zero; low, <2.00 individuals/h; and high, >2.00 individuals/h; Big Flat Brook: zero; low, <2.00 individuals/h; medium, 2.10–7.00 individuals/h; and high, >7.00 individuals/h) based upon results from the qualitative survey, and chose sections within each category for quantitative sampling. Selection of sites to quantitatively survey included a greater proportion of high and medium CPUE sections than low and zero CPUE sections in order to facilitate a more accurate measure of overall population abundance (Thompson 2002; Strayer and Smith 2003; Villella and Smith 2005). We selected a total of 23 sections and 10 sections for quantitative surveys in Big Flat Brook and the Neversink River, respectively (Table 1). In the Neversink River, we based quantitative survey locations off of the most recent 2009 qualitative results, not earlier qualitative surveys (2006–2007) completed in the river.

Qualitative surveys

Within each ∼200 m section, observers snorkeled for a predetermined period of time corresponding to a target coverage of at least five search hours per river kilometer for each river (or 1 h per 200-m section; Table S1). Survey time per section varied depending on the number of observers, section length, and complexity of habitat: smaller sections or those with less in-stream area required less time, while more search time was required for larger or more complex sections. In general, observers snorkeled straight-line transects from the upstream to the downstream border of each section, but they also sought out and investigated unique habitats, channels, and eddies. Observers snorkeled pools up to depths of approximately 5 m in the deepest areas (mainstem Delaware River), although water depths in the surveyed reaches were generally more moderate (<2.00 m). They also spent additional survey time in sections where one or more dwarf wedgemussels were found in an effort to determine if the mussel was a lone individual or part of a cluster of animals within the section. We conducted a single qualitative survey in all streams except in the Neversink River, where we conducted two surveys, one in 2006–2007 and a second survey over a shorter river distance in 2009.

We identified dwarf wedgemussel in the field using key morphological features (Strayer and Jirka 1997). Any mussels picked up from the stream bottom for positive identification were immediately returned by snorkelers to their original locations, positions, and orientations. We did not remove any live animals from any of the rivers; however, we collected voucher shells according to permit stipulations. We converted survey results for each section to CPUE estimates. We used these CPUE values to select a subsample of sections for quantitative surveys for calculating a population estimate.

Quantitative surveys

Within the sections selected for quantitative surveys, we placed 0.25-m2 quadrats on the stream bottom in a systematic sampling design using multiple random starts according to Strayer and Smith (2003) and using the U.S. Geological Survey (USGS) Mussel Estimation Program (v. 1.5.2). We excavated one in four quadrats in both Flat Brooks and the Neversink, and one in three quadrats in the larger mainstem Delaware, to a depth of 10–15 cm in order to detect any subsurface mussels. During excavation, we collected material from the stream bottom and passed it through a 3-mm mesh sieve to detect the presence of small buried juveniles.

We measured dwarf wedgemussels collected during quantitative surveys in all rivers and determined sex of those from Little and Big Flat Brooks and the Neversink River. We plotted size distribution for each quantitatively surveyed river and used a χ2test to test for deviations from a 1:1 sex ratio. We categorized the position of all dwarf wedgemussels within a quadrat as surface (Q) or subsurface (QB) for use in population estimation. In quadrats where a dwarf wedgemussel was found on the surface, we quantified key habitat variables, including quadrat depth, predominant substrate type (or a combination of the two predominant substrate types if they were approximately equal) according to Cummins (1962; silt, <4 mm; sand, 4–16 mm; gravel, 4–64 mm; cobble, 65–256 mm; boulder, >256 mm; bedrock), and percentage of aquatic macrophyte (hereafter “plant coverage”; 0–25%; 26–50%; 51–75%; 76–100%). If a quadrat was excavated and a subsurface dwarf wedgemussel was located, we estimated habitat for that quadrat based on adjoining quadrats.

Population assessment

We used the USGS Mussel Estimation Program (v. 1.5.2; for program download contact David Smith, USGS, [email protected]; see Smith et al. 2000 for the basis and formulae used in this program) to estimate dwarf wedgemussel abundance for each quantitatively surveyed section. In brief, this program estimates abundance based on inputs of surface and corresponding subsurface species occurrences, survey area, quadrat distribution, and number of random starts. In the Delaware River mainstem and Little Flat Brook, we generated population estimates for each of the quantitatively surveyed sections and reported the sum of these values as the total population estimate for these streams. For rivers in which we surveyed only a subsection of dwarf wedgemussel sections (Big Flat Brook and Neversink River), we determined a mean population estimate for low, middle, and high CPUE sections independently. We then assumed these sections to be representative of the remaining qualitative survey sections in that category. We multiplied the mean population estimate for low CPUE sections by the total number of low CPUE sections; we completed similar calculations for middle and high CPUE sections to obtain a total population estimate for the surveyed reach using the methods for stratified sampling presented in Thompson (2002) and Villella and Smith (2005). We calculated upper and lower confidence limits according to Smith (D.R. Smith, USGS Leetown Science Center, personal communication). Because of limited time and funding, we could not complete quantitative surveys in the Paulinskill River.

Qualitative surveys

We spent a total of 2,759 h qualitatively surveying 457 km of river in the Upper Delaware River basin for dwarf wedgemussel between 2000 and 2009 as part of a larger freshwater mussel inventory of the watershed (Table 1). We counted a total of 841 dwarf wedgemussels in qualitative surveys across all five rivers, with the Paulinskill River containing the most (492 individuals) and the Delaware mainstem containing the fewest (14 individuals; Table 2; Table S1). The mean CPUE across all rivers was approximately 0.38 dwarf wedgemussels/h, again with highest CPUE in the Paulinskill River (1.02 mussels/h, with select sections >20.00 mussels/h) and the lowest in the mainstem Delaware River (0.01 mussels/h). The number of sections in which we detected dwarf wedgemussel (hereafter “prevalence”) during qualitative surveys ranged from 4 to 47 across the surveyed drainages. In general, dwarf wedgemussel was more prevalent in Big Flat Brook, the Neversink River (in 2009), and the Paulinskill River, occurring in ≥20 of the sections surveyed, and less prevalent across sections in the Delaware River, Neversink River (in 2006), and Little Flat Brook (≤11 sections surveyed; Table 2). Results of qualitative surveys also indicated that ranges of dwarf wedgemussel varied among streams (Table 2; Figure 2). The longest range (34.4 km) was observed in the Delaware River mainstem, where dwarf wedgemussel also showed a very sparse distribution, occurring in just 9 of 174 ∼200-m sections that constituted its range. Note that we found a single dwarf wedgemussel in qualitative surveys in section DE633 (Table S1), which would extend the range in the mainstem Delaware to approximately 117.0 km and prevalence to 10 of 1,095. However, this individual was located just downstream of the confluence with the Neversink River from where it may have been dislodged. To be conservative, therefore, we excluded it from the range assessment. Ranges in Big Flat Brook, the Neversink, and Paulinskill rivers were substantially smaller (12.5, 7.7, and 7.7 km respectively).

Quantitative surveys and population assessment

Between 2002 and 2009 we searched a total of 25,880 quadrats for dwarf wedgemussel (Table 1; Table S2). We calculated total dwarf wedgemussel population size for the upper Delaware River basin (excluding the Paulinskill River) to be approximately 14,432 animals (Table 3; Table S2). Big Flat Brook had the largest estimated population (7,063; 90% CI, 5,464 and 9,128) and Little Flat Brook the smallest (857; 90% CI, 531 and 1,382). Size frequency distributions were generally bell-shaped (Figure 3) with median shell length ranging from 28 mm in the Neversink River to 34 mm in Little Flat Brook (Table 3; Table S2). We found small (≤10 mm) individuals in all populations. Sex ratios were generally female-biased and ranged between 35% males in the Neversink River to 41% in Little Flat Brook (Table 3). These ratios were significantly different from expected (equal proportion of males and females) in all rivers except Little Flat Brook (Big Flat Brook: χ2 = 6.8, P = 0.009; Little Flat Brook: χ2 = 1.6, P = 0.21; Neversink: χ2 = 7.4, P = 0.007).

We primarily found dwarf wedgemussels on the surface of quadrats with only 13% found fully buried (Table 4). Mean quadrat depth ranged between 0.31 and 0.44 m, but we found individuals in water as shallow as 0.05 m and as deep as 2.00 m. We found individuals in all of the major substrate categories from silt to bedrock and various combinations of these. In the three tributaries, we found dwarf wedgemussel mostly in habitat containing sand as a predominant substrate (81–96%; Table 4); however, we found mussels in the mainstem Delaware most frequently in substrate containing cobble (Table 4). Plant cover was negligible (0–25%) in all quadrats containing dwarf wedgemussel.

Since the time the dwarf wedgemussel was listed as endangered (ESA 1973), its documented distribution in the Delaware River basin was limited to the Neversink River, which during the 1990s supported a large, recruiting population (USFWS 1993; Strayer and Ralley 1993; Michaelson and Neves 1995; Strayer et al. 1996). The objectives of this study were to assess the status and trends of population abundance, distribution, demographics, and microhabitat use of the dwarf wedgemussel in the Upper Delaware River basin. Our findings show that dwarf wedgemussel has a much broader distribution in the upper and middle Delaware River watershed, occurring across at least 71.0 river kilometers in stream reaches of the upper mainstem Delaware River and in several tributary watersheds. It also appears that dwarf wedgemussel in the Neversink River has experienced a shift in within-river distribution since the 1990s and possibly a decline in population size, as researchers have observed sections of river occupied by dwarf wedgemussel before 2005 to contain no mussels (dwarf wedgemussel or other unionid species) after severe flooding that occurred during 2005 (Strayer et al. 1996; Cole and St. John White 2006). Our results document that dwarf wedgemussel has not recovered at sites where it was present prior to 2005, as no dwarf wedgemussels were observed in these reaches during qualitative surveys in 2006 and 2009; however, it is still distributed throughout the Neversink River over a reach of similar length (8.2 km in 2006 and 7.7 km in 2009) to that documented during the 1990s (9.0 km; USFWS 1993; Strayer and Ralley 1993; Strayer et al. 1996). Our results also suggest that dwarf wedgemussel prevalence within this reach increased between 2006 and 2009, equaling 11 and 20 200-m sections respectively during these years, and that while estimated population size in the Neversink River was smaller than those in Big Flat Brook and the Delaware River, these populations had comparable densities (all <0.10). We estimated overall density of dwarf wedgemussels in the Neversink River to be 0.07 individuals/m2 in our 2009 surveys, comparable to values of 0.05 individuals/m2 cited by Strayer et al. (1996), although somewhat lower than values of 0.70 mussels/m2 documented by Smith et al. (2000).

In this study, the largest dwarf wedgemussel populations surveyed quantitatively were in Big Flat Brook. Based on qualitative survey results, another large population, potentially comparable in size or larger than that of Big Flat Brook, currently resides in the Paulinskill River; however, quantitative surveys would be necessary to develop an accurate population estimate. Dwarf wedgemussels were confirmed within the mainstem Delaware River although few individuals were found over a much larger survey area. While the smallest estimated abundances were generated for Little Flat Brook, this was likely a function of drainage area or stream size, and dwarf wedgemussels here, while few in number, occur in close proximity to areas of relatively high dwarf wedgemussel abundance in Big Flat Brook (CPUE ≥ 2.00 mussels/h; density ≥ 0.05 mussels/m2).

Although the survey methodology used in these rivers allowed us to assess distribution of the dwarf wedgemussel across the Delaware River basin, there were several limitations to the methodologies used (Strayer and Smith 2003). First, deep (>1.50 m) and high-velocity areas should have been surveyed with scuba gear, which was beyond the scope of this study. Targeted scuba surveys in deep pools would help to fill this data gap. Additionally, habitat and substrate type vary widely both within and among rivers and may have had consequences for dwarf wedgemussel detection during qualitative surveys. If individuals were undetected in qualitative surveys, those reaches were not quantitatively surveyed; therefore population estimates presented here are conservative estimates of true population size. Future studies should define a standard amount of time to determine whether single individual rare species are part of a larger cluster, as this was not standardized in this study. It should also be noted that inferring patterns of true abundance based on CPUE data can be misleading; these relationships should be verified in future studies across species.

Sex ratio, size distribution, and habitat were generally similar among all rivers. All surveyed rivers contained small individuals with shell length ≤ 10 mm. Based on growth curves for the Neversink River (Michaelson and Neves 1995) these individuals are presumably young (<1 y), indicating recent recruitment. Over 8% (2 out of 24) of mainstem Delaware River mussels fell into this size category; this was the highest percentage of young mussels found in any of the surveyed rivers despite the small population size of dwarf wedgemussel overall in the Delaware, a phenomenon that warrants further investigation. Sex-ratios were female-biased in all rivers, although not statistically different from equal in Little Flat Brook. Unequal sex ratios in mussels can be common, but extremely skewed ratios may be an indication of population decline (see Galbraith and Vaughn 2011 and references therein for a full discussion of possible explanations for skewed sex ratios). Further research on dwarf wedgemussel reproduction as well as development of length-at-age curves is necessary to fully evaluate dwarf wedgemussel demographics within the Delaware River basin. Habitat for this species tended to be shallow areas (potentially as a function of survey bias) and small substrate. Dwarf wedgemussel was found primarily in sandy substrate in the tributaries but was found in cobble in the mainstem, which may be a function of overall larger substrate sizes in the mainstem in general. The majority of mussels were not buried below the surface in surveys, but burrowing can vary seasonally and with reproductive status (Balfour and Smock 1995; Amyot and Downing 1997). Smith et al. (2000) found higher percentages of buried individuals in the Neversink, Connecticut, and Ashuelot rivers (36, 45, and 78% respectively).

The populations assessed in this survey, with the exception of the Neversink River, were undocumented at the time of recovery plan drafting and preliminarily meet several of the criteria outlined in the plan (USFWS 1993). Whether these populations are large enough to maintain genetic variability and whether recruitment is high enough to maintain a stable population has yet to be assessed. Genetic analyses of dwarf wedgemussel in the Delaware Basin indicated substantial genetic variation within populations as well as significant isolation-by-distance among populations (Playfoot 2004). Further evaluation of the relationship between genetic structure and population size, distribution, and hypothesized host fish use, and whether current populations and levels of reproduction can maintain this diversity, is warranted.

The degrees of protection and exposure to disturbance regimes vary widely for dwarf wedgemussel populations in the Delaware River basin. Big Flat Brook, Little Flat Brook, and the mainstem Delaware River contain a mixture of federal land, state game lands, and private property, offering some degree of protection from certain types of development; however, they are subject to other risk factors including highly regulated flows in the Delaware River mainstem and agriculture throughout large parts of the watershed. The Neversink and Paulinskill rivers are entirely on private land, but do receive state protection. As in the upper Delaware River, streamflow in the Neversink River is regulated by reservoir releases. Recent studies have evaluated the effects of flow management on dwarf wedgemussel populations in the mainstem Delaware and suggest that the degree of flow stability influences dwarf wedgemussel distribution (Bovee et al. 2007; Cole et al. 2008; Maloney et al. 2012). This is likely a critical consideration in protecting and restoring dwarf wedgemussel populations in the Delaware River basin, particularly in regulated reaches like the Upper Delaware River and Neversink River, and should be considered in the maintenance of current populations or in dwarf wedgemussel recovery efforts.

Caution is warranted when comparing population estimates among the five rivers studied here as data were collected over a span of nearly 10 y. Furthermore, while methodology was largely consistent among rivers, it was influenced to some extent by funding and manpower. New surveys are needed develop an updated and more comprehensive understanding of dwarf wedgemussel populations in this watershed. Although dwarf wedgemussels have been observed at known sites in the Delaware River since the original surveys in the early 2000s, new quantitative surveys of the Delaware River mainstem following the 2005 flooding event would be useful to confirm the preflood population estimates. Additionally, quantitative studies in the Paulinskill River and both qualitative and quantitative studies in the Pequest River, another dwarf wedgemussel–containing tributary, are necessary to fill data gaps. Establishing long-term monitoring sites (for both qualitative and quantitative surveys) at select locations across the entire Delaware River basin may provide useful information on population trajectories of this and other mussel species, along with changing habitat conditions, and help meet the needs addressed in the dwarf wedgemussel recovery plan.

Please note: The Journal of Fish and Wildlife Management is not responsible for the content or functionality of any supplemental material. Queries should be directed to the corresponding authors for the article.

Table S1. Results from dwarf wedgemussel (DWM) Alasmidonta heterodon qualitative freshwater mussel surveys conducted in five rivers (River) in the Delaware River basin between 2000 and 2009 (Year). The table describes the length in meters (Length) of each uniquely identified section (Section) of river; the approximate time in hours (Time) spent surveying each section; the number of individual dwarf wedgemussels found in each section (No. DWM); and the dwarf wedgemussel catch per unit effort (DWM CPUE), or number of individuals collected per hour of survey time.

Found at DOI: http://dx.doi.org/10.3996/112014-JFWM-084.S1 (130 KB XLSX).

Table S2. Results of quantitative freshwater mussel surveys for dwarf wedgemussel Alasmidonta heterodon conducted in five rivers (River) in the Delaware River basin between 2000 and 2009. The table describes the river section (Section) from the qualitative survey (Table S1) that was quantitatively surveyed; the corresponding number of quadrats surveyed (No. quadrats); dwarf wedgemussel catch per unit effort (CPUE; from the qualitative survey, Table S1); dwarf wedgemussel density in number of individuals per square meter (Density) and standard error (SE); the estimated abundance (Abundance) in number of individual dwarf wedgemussel calculated by the USGS Mussel Estimation Program (v. 1.5.2); and the number of individual dwarf wedgemussels found visible at the quadrat surface (Q) or buried below the surface (QB) in quadrats. Quadrat-scale habitat characteristics of each dwarf wedgemussel are also presented by river section including the depth in meters of each quadrat (Depth), the dominant substrate type or substrate combination in each quadrat (Substrate; SI, silt; SA, sand; GR, gravel; CO, cobble; BO, boulder; BE, bedrock; see methods for size description of each substrate category), the percentage of aquatic macrophytes observed in each quadrat (% Plant), the size in millimeters of each individual dwarf wedgemussel (Size) where XXX denotes no measurement was collected, and the sex of each individual dwarf wedgemussel (Sex) where XXX denotes the individual was not able to be sexed. Note: data presented for the Neversink River are from 2009 as quantitative surveys were not completed in 2006–2007.

Found at DOI: http://dx.doi.org/10.3996/112014-JFWM-084.S2 (130 KB XLSX).

Reference S1. Bovee KD, Waddle TJ, Bartholow J, Burris L. 2007. A decision support framework for water management in the Upper Delaware River. Open-File Report, U.S. Geological Survey, Report OF 2007-1172. U.S. Geological Survey, Reston Virginia.

Found at DOI: http://dx.doi.org/10.3996/112014-JFWM-084.S3; also available at https://www.fort.usgs.gov/sites/default/files/products/publications/21938/21938.pdf (6176 KB PDF).

Reference S2. Cole JC, Townsend PA, Eshleman KN. 2008. Predicting flow and temperature regimes at three Alasmidonta heterodon locations in the Delaware River. Technical Report NPS/NER/NRTR—2008/109. National Park Service, Philadelphia, Pennsylvania.

Found at DOI: http://dx.doi.org/10.3996/112014-JFWM-084.S4; also available at http://irmafiles.nps.gov/reference/holding/152993?accessType=DOWNLOAD (2632 KB PDF).

Reference S3. Playfoot KM. 2004. Microsatellite DNA markers detect significant population structure of Alasmidonta heterodon within the Delaware River basin. Masters thesis. State College: The Pennsylvania State University.

Found at DOI: http://dx.doi.org/10.3996/112014-JFWM-084.S5 (547 KB PDF).

Reference S4. St. John White B. 2007. Evaluation of fish host suitability for the endangered dwarf wedgemussel Alasmidonta heterodon. Masters thesis. State College: The Pennsylvania State University.

Found at DOI: http://dx.doi.org/10.3996/112014-JFWM-084.S6; also available at http://www.fwspubs.org/doi/suppl/10.3996/102012-JFWM-094/suppl_file/10.3996_102012-jfwm-094.s5.pdf (1423 KB PDF).

Reference S5. Suro, TP, Firda, GD. 2006. Flood of April 2–3, 2005, Neversink River Basin, New York. U. S. Geological Survey Open-File Report 2006-1319.

Found at DOI: http://dx.doi.org/10.3996/112014-JFWM-084.S7; also available at http://pubs.usgs.gov/of/2006/1319/ (17776 KB PDF).

Reference S6. [USFWS] U.S. Fish and Wildlife Service. 1993. Dwarf wedge mussel Alasmidonta heterodon recovery plan. Hadley Massachusetts: U.S. Fish and Wildlife Service, Region Five.

Found at DOI: http://dx.doi.org/10.3996/112014-JFWM-084.S8; also available at http://www.fws.gov/northeast/pafo/pdf/Dwarf%20wedgemussel%20Recovery%20Plan.pdf (2893 KB PDF).

Assistance in surveys and field data recording was provided by Susan Bolden, Travis Brandt, Ryan Brown, Cara Campbell, Casey Carleton, Andrew Cole, Sue Wolinsky Comlish, Angie Drummond, Heather Hammond, Kira Hawk, Vinca Krajewski, Kelly McDivitt, Jake Robinson, Renee Rogers, Cheryl Engelhardt Rossi, Kristine Shaw, Katie Staudenmeier, Shauna Stoll, Erika Tokarz, George Velez, Sebastian Velez, Nevin Welte, Sara Welte, and Nina White of USGS. Sofia Luckenbill assisted in data summarization and analysis. We thank Don Hamilton and other staff at the National Park Service for their support and assistance in the field and for comments provided on the manuscript; David Smith for assisting in survey design; David Strayer for confirming identification of voucher shells; and the anonymous reviewers and Associate Editor of the journal for their comments that greatly improved the manuscript. This work was conducted under the following permits: New York Scientific Collection/Possession License No. LCP02-138, New York Endangered/Threatened Species License No. ESP02-0074; Pennsylvania Type II Permit No. 037; New Jersey Scientific Collecting Permit Nos. SC29027, SC28034, SC27017, SC26109, SC21055, SC22056; and National Park Service Scientific Research and Collecting Permit Nos. DEWA-00-35, DEWA-2001-SCI-003, DEWA-2002-SCI-0026, DEWA-2004-SCI-0017, DEWA-2006-SCI-0013, DEWA-2008-SCI-0015, UPDE-00-01, UPDE-2001-SCI-0004, UPDE-2002-SCI-0003. This study was funded by the U.S. Fish and Wildlife Service and the National Park Service. The USGS Fisheries Program also contributed to this work.

Any use of trade, product, website, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government.

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Author notes

Citation: Galbraith HS, Lellis WA, Cole JC, Blakeslee CJ, St. John White B. 2016. Population demographics for the federally endangered dwarf wedgemussel. Journal of Fish and Wildlife Management 7(2):377–387; e1944-687X. doi: 10.3996/112014-JFWM-084

The findings and conclusions in this article are those of the author(s) and do not necessarily represent the views of the U.S. Fish and Wildlife Service.

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