[Federal Register: October 9, 2001 (Volume 66, Number 195)] [Rules and Regulations] [Page 51322-51339] From the Federal Register Online via GPO Access [wais.access.gpo.gov] [DOCID:fr09oc01-17] ======================================================================= ----------------------------------------------------------------------- DEPARTMENT OF THE INTERIOR Fish and Wildlife Service 50 CFR Part 17 RIN 1018-AF57 Endangered and Threatened Wildlife and Plants; Determination of Endangered Status for the Scaleshell Mussel AGENCY: Fish and Wildlife Service, Interior. ACTION: Final rule. ----------------------------------------------------------------------- SUMMARY: We, the U.S. Fish and Wildlife Service (Service), determine the scaleshell mussel (Leptodea leptodon) to be an endangered species under the Endangered Species Act of 1973, as amended (Act). The scaleshell mussel historically occurred in 55 rivers in 13 states in the eastern United States. Currently, the species is known to exist in 14 rivers (and may occur in 6 others) within the Mississippi River Basin in Missouri, Oklahoma, and Arkansas. Its abundance and distribution have decreased markedly due to habitat loss and adverse effects associated with water quality degradation, sedimentation, channelization, sand and gravel mining, dredging, and reservoir construction. DATES: This final rule is effective on November 8, 2001. ADDRESSES: The complete file for this rule is available for inspection, by appointment, during normal business hours at the Columbia Field Office, U.S. Fish and Wildlife Service, 608 East Cherry Street, Room 200, Columbia, Missouri 65201. FOR FURTHER INFORMATION CONTACT: Andy Roberts (at the above address or telephone 573-876-1911, ext. 110; fax 573-876-1914). TTY users may contact us through the Federal Relay Service at 1-800-877-8339. SUPPLEMENTARY INFORMATION: Background Buchanan (1980), Cummings and Mayer (1992), Oesch (1995), and Watters (1995) provide descriptions of the scaleshell mussel. The shell grows to approximately three to ten centimeters (one to four inches) in length. The shells are elongate, very thin, and compressed. The anterior (front) end is rounded. In males, the posterior (rear) end is bluntly pointed. In females, the periostracum (the outside layer or covering of the shell) forms a wavy, fluted extension of the posterior end of the shell. The dorsal (top) margin is straight and the ventral (bottom) margin is gently rounded. Beaks (the raised or domed part of the dorsal margin of the shell) are small and low, and nearly even with the hinge line. The beak sculpture is inconspicuously compressed and consists of four or five double-looped ridges. The periostracum is smooth, yellowish green or brown, with numerous faint green rays. The pseudocardinal teeth (the triangular, often serrated, teeth located on the upper part of the shell) are reduced to a small thickened ridge. The lateral teeth (the elongated teeth along the hinge line of the shell) are moderately long with two indistinct teeth occurring in the left valve (shell) and one fine tooth in the right. The beak cavity (a cavity located inside the shell that extends into the beak) is very shallow. The nacre (the interior layer of the shell) is pinkish white or light purple and highly iridescent. Life History The biology of the scaleshell mussel is similar to the biology of other bivalved mollusks belonging to the family Unionidae. Adult unionids are filter-feeders, spending their entire lives partially or completely buried in the stream bottom (Murray and Leonard 1962). The posterior margin of the shell is usually exposed and the siphons extended to facilitate feeding. During periods of activity, movement is accomplished by extending and contracting a single muscular foot between the valves. Extension of the foot also enables the mussel to wedge itself into the river bottom. Their food includes detritus (disintegrated organic material), plankton, and other microorganisms (Fuller 1974). Some freshwater mussel species are long-lived. Individuals of many species live more than 10 years and some have been reported to live over 100 years (Cummings and Mayer 1992). Unionids have an unusual and complex mode of reproduction, which includes a brief, obligatory parasitic [[Page 51323]] stage on fish. Males release sperm into the water column in the spring, summer, or early fall, and females using the incurrent water flow draw in the sperm. Fertilization takes place in the shell of the female. Fertilized eggs develop into microscopic larvae (glochidia) and are brooded within special gill chambers of the female. Once the glochidia are mature, they are expelled into the water where they must quickly attach to the gills or the fins of an appropriate fish host to complete development. Following proper host infestation, glochidia transform into juveniles and excyst (drop off). Juveniles must drop off into suitable habitat to survive. Host fish specificity varies among unionids. Some mussel species appear to require a single host species, while others can transform their glochidia into juvenile mussels on several fish species. For further information on the life history of freshwater mussels, see Gordon and Layzer (1989) and Watters (1995). Mussel biologists know relatively little about the specific life history requirements of the scaleshell mussel. Baker (1928) surmised that the scaleshell mussel is a long-term brooder (spawns in fall months and females brood the larvae in their gills until the following spring or summer). Glochidia found in the gill chambers in September, October, November, and March support that conclusion (Gordon 1991). The scaleshell mussel uses the freshwater drum (Aplodinotus grunniens) as the fish host for its larvae (Chris Barnhart, Southwest Missouri State University, pers. comm. 1998). Other species in the genus Leptodea and a closely related genus Potamilus are also known to use freshwater drum exclusively as a host (Watters 1994). Little is known about the life expectancy of the scaleshell mussel. However, recent collections from Missouri indicate that it is relatively short-lived compared to other species. A sample of 33 dead specimens and 2 living individuals collected in 2000 from a Gasconade River site did not contain any individuals exceeding seven years old (Chris Barnhart, pers. comm. 2000). Likewise, no individuals over six years old were observed out of 44 living individuals collected in 1997 from the Meramec Basin (Roberts and Bruenderman 2000). Based on these collections, it appears that the life expectancy of the scaleshell mussel may be less than 10 years. In addition, the sex ratio of the above collections are significantly different from a 50/50 ratio (Chi- Square Test, P 0.05). The Gasconade collection only contained eight females (including one living) out of 35 individuals, and the Meramec Basin collection only contained 15 females out of 44 living individuals. The reason females appear to be less common than males in the Gasconade River and Meramec Basin is unknown. Habitat Characteristics The scaleshell mussel occurs in medium to large rivers with low to moderate gradients in a variety of stream habitats. Buchanan (1980, 1994) and Gordon (1991) reported the scaleshell mussel from riffle areas with substrate consisting of gravel, cobble, boulder, and occasionally mud or sand. Oesch (1995) considered the scaleshell mussel a typical riffle species, occurring only in clear, unpolluted water with good current. Conversely, Call (1900), Goodrich and Van der Schalie (1944), and Cummings and Mayer (1992) reported collections from muddy bottoms of medium-sized and large rivers. Roberts and Bruenderman (2000) collected the scaleshell mussel primarily from mussel beds (areas with a high concentration of mussels that contain more than one species) with stable, gravel substrates. The characteristic common to these sites appears to be a stable stream bed and good water quality. These habitat observations are consistent with the current distribution of the scaleshell mussel. The scaleshell mussel is restricted to rivers that have maintained relatively good water quality (Oesch 1995) and to river stretches with stable channels (Buchanan 1980, Harris 1992). The scaleshell mussel is also usually collected in mussel beds in association with a high diversity of other mussel species. Distribution and Abundance The scaleshell mussel historically occurred in 13 states in the eastern United States. While the scaleshell mussel had a broad distribution, it appears that it was a rare species locally (Gordon 1991, Oesch 1995, Call 1900). Williams et al. (1993) reported the historical range as Alabama, Arkansas, Illinois, Indiana, Iowa, Kentucky, Missouri, Ohio, Oklahoma, South Dakota, Tennessee, and Wisconsin. Historical records also exist for the Minnesota River, Minnesota (Clarke 1996). Williams et al. (1993) also listed Michigan and Mississippi as part of the scaleshell mussel's range, but no valid records exist in these states. Therefore, its presence cannot be confirmed (Bob Jones, Mississippi Wildlife Fisheries and Parks, Museum of Natural Science, pers. comm. 2000; Szymanski 1998). Gordon (1991) included a portion of the St. Lawrence drainage in describing the distribution of the scaleshell mussel. However, the specimens that were the source of the St. Lawrence River record were later identified as wingless examples of Leptodea fragilis (fragile papershell), which are often seen in New York (David Strayer, Institute of Ecosystem Studies, New York, in litt. 1995). Given this and that no other authentic specimens have been found (David Stansbery, Ohio State Museum, in litt. 1995), the historical occurrence of the species in St. Lawrence Basin is doubtful. Within the last 50 years the scaleshell mussel has become increasingly rare and its range greatly restricted. Historically, the scaleshell mussel occurred in 55 rivers. Today, the species is known from only 14 rivers including the Meramec, Bourbeuse, Big, Gasconade, and Osage Rivers in Missouri; Frog Bayou and the St. Francis, Spring, South Fork Spring, South Fourche LaFave, and White Rivers in Arkansas; and the Little, Mountain Fork, and Kiamichi Rivers in Oklahoma. An additional six rivers (Cossatot, Little Missouri, Saline, and Strawberry Rivers, and Myatt and Gates Creeks) in Arkansas and Oklahoma may support the scaleshell mussel, but the existence of the species in these rivers is uncertain. With the exception of the Meramec, Bourbeuse, and Gasconade Rivers, all rivers listed as supporting the scaleshell mussel are based on the collection of a few or a single individual specimen. Assessment of the Presumed Health of Individual Populations For the purposes of this rule, the term ``population'' is used in a geographical sense and, unless otherwise indicated, is defined as all individuals living in one river or stream. By using this term we do not imply that a scaleshell mussel population is currently reproducing or that it is a distinct genetic unit. Using the term in this way allows the status, trends, and threats to be discussed separately for each river where the scaleshell mussel occurs, improving the clarity of the discussion. Due to the low densities of current scaleshell mussel populations, ascertaining status (an assessment of the current existence of a population) and trends (an assessment of change in a population's numbers and its probable future condition) is difficult. To facilitate population comparisons, a single classification system was devised to evaluate the probable current health of individual populations. The indicators of (or criteria for) the presumed health of scaleshell mussel populations are as follows. The [[Page 51324]] presumed health of a population is considered ``stable'' if (1) there is no evidence of significant habitat loss or degradation, and (2) there has been post-1980 collection of live or fresh dead mussels and, if surveys were thorough, evidence of recruitment was found. The presumed health of a population is considered ``declining'' if (1) habitat is limiting due to its small size, or a significant decrease in habitat quality or quantity has occurred, (2) there is no evidence of recruitment despite one or more thorough surveys, or (3) a significant decline in number of individual mussels has occurred. The presumed health of a population is considered ``extirpated'' if (1) despite one or more thorough post-1980 surveys, no scaleshell mussels, or only old dead shells, have been found, or (2) all known suitable habitat has been destroyed. The presumed health of a population is considered ``unknown'' if the available information is inadequate to place the population in one of the above categories. In a few cases, additional biological information not listed above was used to categorize a population that otherwise would have been called ``unknown'' or which appeared to fit into multiple categories. Based on the above criteria, 14 scaleshell mussel populations are considered extant. Of these populations, the presumed health of 1 is thought to be stable and 13 are believed to be declining. Six other populations may also be extant, but their health is unknown due to lack of recent collections or surveys. The 14 extant populations and 6 potentially extant populations are listed in Table 1 and included in the discussions below. Table 1.--Presumed Population Health of Extant and Potentially Extant Scaleshell Mussel Populations. S = stable, D = declining, UK = unknown ------------------------------------------------------------------------ Population Presumed health ------------------------------------------------------------------------ Big (MO)................................... D Bourbeuse (MO)............................. D Cossatot (AR).............................. UK Frog Bayou (AR)............................ D Gates Creek (OK)........................... UK Gasconade (MO)............................. D Kiamichi (OK).............................. D Little Missouri (AR)....................... UK Little (OK)................................ D Meramec (MO)............................... D Mountain Fork (OK)......................... D Myatt Creek (AR)........................... UK Osage River (MO)........................... D St. Francis (AR)........................... D Saline (AR)................................ UK South Fork Spring (AR)..................... S South Fourche LaFave (AR).................. D Spring River (AR).......................... D Strawberry (AR)............................ UK White River (AR)........................... D ------------------------------------------------------------------------ River Basin Specific Discussion of the Scaleshell Mussel Status Upper Mississippi River Basin The scaleshell mussel formerly occurred in eight rivers and tributaries within the upper Mississippi River Basin, including the Mississippi River in Illinois, Iowa, and Wisconsin; the Minnesota River in Minnesota; Burdett's Slough in Iowa; the Iowa and Cedar Rivers in Iowa; and the Illinois, Sangamon, and Pecatonica Rivers in Illinois. However, the scaleshell mussel has not been found for more than 50 years in the upper Mississippi River Basin and is believed extirpated from that basin (Kevin Cummings, Illinois Natural History Survey, in litt. 1994). Middle Mississippi River Basin Historically, the scaleshell mussel occurred in 26 rivers and tributaries within the middle Mississippi River Basin including the Kaskaskia River in Illinois; the mainstem Ohio River in Kentucky and Ohio; the Wabash River in Illinois and Indiana; the White River and Sugar Creek in Indiana; the Green and Licking Rivers in Kentucky; the Scioto, St. Mary's, and East Fork Little Miami Rivers in Ohio; the Cumberland River in Kentucky and Tennessee; Beaver Creek in Kentucky; Caney Fork in Tennessee; the Tennessee River in Alabama and Tennessee; the Clinch, Holston, and Duck Rivers in Tennessee; Auxvasse Creek in Missouri; the Meramec, Bourbeuse, South Grand, Gasconade, Big, Osage, and Big Piney Rivers in Missouri; and the mainstem Missouri River in South Dakota and Missouri. The scaleshell mussel has been extirpated from most of the middle Mississippi River Basin. Currently, the scaleshell mussel is extant in five rivers within the Meramec River basin and tributaries of the Missouri River drainages in Missouri. Ohio River Drainage--The scaleshell mussel has been extirpated from the entire Ohio River system. The most recent collection date from the Ohio River Basin is 1964 from the Greene River (Wayne Davis, Kentucky Department of Fish and Wildlife, in litt. 1994). All other records are pre-1950 (Kevin Cummings, in litt. 1994; Catherine Gremillion-Smith, Indiana Department of Natural Resources, in litt. 1994; Ron Cicerello, Kentucky Department of Fish and Wildlife, in litt., 1994; Paul Parmelee, University of Tennessee, pers. comm. 1995). Meramec River Basin (Missouri)--In 1979, Buchanan surveyed for mussels at 198 sites within the Meramec River Basin (Buchanan 1980). Of these sites, 14 had evidence of live or dead scaleshell mussels. Seven of the 14 sites were in the lower 180 kilometers (km) (112 miles (mi)) of the Meramec River, five in the lower 87 km (54 mi) of the Bourbeuse River, and two in the lower 16 km (10 mi) of the Big River. Buchanan found that the species comprised less than 0.1 percent of the 20,589 living mussels he examined in the basin. He collected live scaleshell mussels at only four sites, three in the Meramec and one in the Bourbeuse. Although the lower 174 km (108 mi) of the Meramec River had suitable habitat for many rare species, live scaleshell mussels were found only in the lower 64 km (40 mi) (Buchanan 1980). Both the Bourbeuse and Big Rivers had lower species diversity and less suitable habitat than the Meramec River. Suitable habitat occurs only in the lower 87 km (54 mi) of the Bourbeuse River and lower 16 km (10 mi) of the Big River (Buchanan 1980). The Missouri Department of Conservation (MDC) sampled 78 sites in an intensive resurvey of the Meramec River basin in 1997 (Roberts and Bruenderman 2000). Similar to Buchanan's findings (1980), scaleshell mussels represented only 0.4 percent of the living mussels. Live specimens were collected from the mainstem Meramec River (34 specimens from 9 sites), the Bourbeuse River (10 specimens from 5 sites), and the Big River (2 specimens from 1 site). In addition to the nine sites surveyed by Buchanan (1979), new sites were included in the 1997 survey. Living or dead scaleshell mussels were found at four of the five sites in the Meramec River and two of the four sites in the Bourbeuse River. The three sites where the presence of scaleshell mussels was not reconfirmed no longer support suitable mussel habitat due to stream bed degradation. Other species that were found in mussel beds at those sites in the earlier surveys were no longer present in 1997. Although portions of the Meramec River basin continue to provide suitable habitat, mussel species diversity and abundance have declined noticeably since 1980 and [[Page 51325]] significant losses of mussel habitat have occurred (Roberts and Bruenderman 2000). The number of scaleshell mussel specimens the MDC collected in 1997 is greater than that reported by Buchanan's study (Buchanan 1980); however, the small number of specimens collected, especially from the Bourbeuse and Big Rivers, indicates that the long-term viability of these populations is tenuous. Moreover, the long-term persistence of populations in the Meramec Basin is in question because of the limited availability of mussel habitat and the loss of mussel beds since 1980 from bank and channel degradation, sedimentation, and eutrophication (excessive fertilization caused by pollution of plant nutrients) (Roberts and Bruenderman 2000; Alan Buchanan, MDC, in litt. 1997; Sue Bruenderman, MDC, pers. comm. 1998). Missouri River drainage (South Dakota and Missouri)--Within the Missouri River drainage, Buchanan (1980, 1994) and Oesch (1995) reported scaleshell mussels from the Missouri, Gasconade, Big Piney, South Grand, Osage Rivers, and Auxvasse Creek. The last collection of scaleshell mussels from Auxvasse Creek was in the late 1960s (Alan Buchanan, in litt. 1997). Similarly, the last known collection date for the South Grand is the early 1970s. This collection site is now inundated by Truman Lake and is unsuitable for the scaleshell mussel (Alan Buchanan, in litt. 1997). A single, fresh dead specimen was collected from Big Piney River in 1981 (Sue Bruenderman, in litt. 1998). However, the scaleshell mussel has not been found in recent surveys of this river. Between 1994 and 1996, 70 sites were sampled in the Big Piney River from the mouth to the headwaters. While 3,331 mussels of 26 species were collected, no evidence of scaleshell mussels were found (Janet Sternberg, MDC, pers. comm. 2000). Another survey was conducted in 1998, in which 10 sites were sampled between river miles 53.6 and 96.0. Over 1,000 living mussels were collected representing 15 species, but no living or dead scaleshell mussels were found (Sue Bruenderman, pers. comm. 2000). Only two records (both single dead shells) of scaleshell mussels exist for the mainstem of the Missouri River. In 1981 and 1982, the Missouri River was surveyed from Santee to Omaha, Nebraska (Hoke 1983). A single fresh dead shell was found during this study just below Gavin's Point Dam, South Dakota. This occurrence represents the westernmost record of the scaleshell mussel in North America. However, this species has not been found in subsequent surveys on the Missouri River just below Gavin's Point dam. In 1995, Clarke (1996) found no evidence of scaleshell mussels in a survey conducted from Gavin's Point Dam to 48 river km (30 mi) downstream. However, high water conditions limited Clark's search efforts, and only 10 individual mussels were found. In 1999, the Omaha District of the U.S. Army Corps of Engineers (Corps) funded a mussel survey between Gavin's Point Dam and Ponca, Nebraska, a distance of 96 river km (60 mi). In all, 355 live and 1,709 dead individual mussels were collected representing 16 species, but no living or dead scaleshell mussels were found (Candace M. Gordon, Corps, Omaha District, in litt. 2000). The second scaleshell mussel record from the mainstem of the Missouri River is a single fresh dead individual that was collected in 1990 from Gasconade County, Missouri. This specimen was found during an extensive survey conducted from Gavin's Point Dam to St. Louis (Hoke 2000). However, the site of this collection was subsequently destroyed. Since no living scaleshell mussel has been found in the Missouri River, its habitat cannot be determined. However, both dead shells were collected from areas shielded from the main flow of the river in relatively stable, sandy bottoms with moderate current (Hoke 2000). Hoke (2000) described scaleshell mussel as ``extremely rare'' and its habitat ``very uncommon * * * and existing in only widely separated locals'' in the Missouri River. Based on the criteria used to assign presumed health to scaleshell mussel populations (Table 1), we consider this potential population to be extirpated at this time. Of the two known Missouri River records for scaleshell mussel, one locality has been destroyed and recent surveys have not found any evidence of this species at or in the vicinity of the other site. Further, no other scaleshell mussel specimens were found during Hoke's survey from Gavin's Point Dam to St. Louis. More information is needed on the existence of the scaleshell mussel and its habitat in the Missouri River. Furthermore, more information is needed on the location of sampling sites, distribution and habitat use of mussels, etc. from Hoke's survey work on the Missouri River, which is unavailable at this time. Buchanan (1994) surveyed the lower 137 km (85 mi) of the Gasconade River, and documented 36 species of freshwater mussels. He collected scaleshell mussel specimens at eight sites between river miles 6.0 and 57.7. Buchanan found only dead shells at two sites and eight live specimens from the remaining six sites. Overall, scaleshell mussels comprised less than 0.1 percent of the mussels collected. In 1998-99, the Gasconade River was surveyed at 46 sites from mile 92.0 to 256.0. At sites where scaleshell mussels were collected, living individuals represented less than 0.5 percent of the total number of mussels found. A total of 12 living scaleshell mussels were found at 9 sites, and dead shells were found at an additional 10 sites between river miles 92.0 and 230.3 (Sue Bruenderman, pers. comm. 2000). A scaleshell mussel has recently been discovered in the lower Osage River in Osage County, Missouri. On July 16, 2001, one live male specimen was found at river mile 20 (Heidi Dunn, pers. comm.). This individual was found during a mussel survey that is currently underway in the lower 80 miles of the Osage River and its tributaries. To date, 33 sites have been surveyed including 24 in the mainstem. A total of 3,904 living mussels have been found representing 29 living species. No other evidence of scaleshell mussels were found during the survey, but more intensive sampling is planned for these same sites in the near future. Until this recent discovery, the scaleshell mussel had never been reported from the Osage system in past surveys. Utterback (1917) found 34 species in the basin. No other information is available because his notes and collections have since been lost. Oesch (1995) collected mussels in the 1970s at a number of sites in the basin and reported 39 species. In 1980, a detailed study of mussel distribution was conducted by Grace and Buchanan (1981) of the Lower 80 miles of the Osage River and two tributaries below Bagnell Dam. A total of 43 sites were surveyed and 21,593 living mussels were found representing 36 species. No evidence of scaleshell mussels was found in any of these surveys. This new record of the scaleshell mussel does not significantly increase its range or lessen its risk of extinction. Similar to other records for the species, the one individual found indicates that a small population is present. No other evidence of the species was found during the 2001 survey. If a significant population of scaleshell mussels existed in the Osage River, dead shells would have been found. This is because dead shells accumulate over time, which makes them easier to detect than live specimens. Additionally, there are significant threats to scaleshell mussel in the Osage River from the operation of Bagnell Dam and instream gravel mining. Due to these habitat conditions, we categorized the Osage River [[Page 51326]] scaleshell mussel population's presumed health as declining. Middle Mississippi River Basin summary--Of the 26 rivers and tributaries in the middle Mississippi River Basin that historically supported scaleshell mussels, the species is still present in 5 including the Meramec, Bourbeuse, Big, Osage, and Gasconade Rivers. The presumed health of all of these populations is thought to be declining. Lower Mississippi River Basin The scaleshell mussel historically occupied 21 rivers and tributaries in the lower Mississippi River Basin. These include the St. Francis, White, James, Spring, Little Missouri, Middle Fork Little Red, Saline (of the Ouachita River), Ouachita, Cossatot, Saline (of the Little River), South Fourche LaFave, Mulberry, and Strawberry Rivers in Arkansas; South Fork Spring, Frog Bayou, and Myatt Creek in Arkansas; Poteau, Little, and Kiamichi Rivers in Oklahoma; and Gates Creek and Mountain Fork in Oklahoma. These rivers are organized and discussed below according to drainage (St. Francis, White, Arkansas, and Red River drainages). St. Francis River drainage (Arkansas)--Bates and Dennis (1983), Clarke (1985), and Ahlstedt and Jenkinson (1987) conducted mussel surveys on the St. Francis River in Arkansas and Missouri. Of these surveys, scaleshell mussels were only documented from two sites, both of which are single-specimen records (Clarke 1985). Records of dead shells of various species indicate that at one time freshwater mussels occurred throughout the river (Bates and Dennis 1983). Bates and Dennis (1983) determined that of the 54 sites sampled, 15 were productive, 10 marginal, and 29 had either no shells or dead specimens only; scaleshell mussels were not documented at any of the 54 sites. They identified 77 km (48 mi.) of habitat generally suitable for mussels: Wappapello Dam to Mingo Ditch, Missouri; Parkin to Madison, Arkansas; and Marianna to the confluence with the Mississippi River at Helena, Arkansas. They indicated that the remaining portions of the river were no longer suitable for mussels. If the scaleshell mussel is extant in the St. Francis River, it is restricted to the few patches of suitable habitat. White River drainage (Arkansas)--Clarke (1996) noted a 1902 collection of a single specimen from the White River near Garfield, Arkansas. A late 1970s survey of the White River between Beaver Reservoir and its headwaters failed to relocate live or dead scaleshell mussel individuals. However, in 1999, a single live specimen was collected from the White River near Newport by John Harris (John Harris, Arkansas Department of Transportation, pers. comm. 2000). Navigation maintenance activities have relegated the mussel fauna to a few refugial sites (Bates and Dennis 1983). Specimens have not been collected from the James River, a tributary of the White River, since before 1950 (Clarke 1996). An eight-mile section of the Spring River in Arkansas supports a diverse assemblage of freshwater mussels (Gordon et al. 1984, Arkansas Highway and Transportation Dept 1984, Miller and Hartfield 1986). The collections from this river total eight scaleshell mussel specimens (Kevin Cummings, in litt. 1994; Clarke 1996, Arkansas State Highway and Transportation Department, 1984). Gordon et al. (1984) surveyed the river and reported suitable mussel habitat between river miles 3.2 and 11.0, although species richness below river mile 9 had declined markedly compared to past surveys. Gordon et al. (1984), as well as Miller and Hartfield (1986), reported that the lower 5.0 km (3.0 mi) of river were completely depleted of mussels and contained no suitable habitat. Harris did not find scaleshell mussels in a 1993 survey of the Spring River (John Harris, in litt. 1997). Scaleshell mussels were collected from the South Fork of the Spring River in 1983 and 1990. During the 1983 survey, Harris (in litt. 1997) collected four specimens near Saddle, Arkansas, and one specimen and one valve north of Hunt, Arkansas. During a subsequent visit in 1990, Harris collected young adults (Harris, pers. comm. 1995). Although juveniles were not found, the presence of young adults suggests that reproduction recently occurred. Records of scaleshell mussels from the Strawberry River and the Myatt Creek are based on single specimen collections, both made in 1996 (John Harris, in litt. 1997). Harris collected a live specimen from the Strawberry River near the confluence with Clayton Creek in Lawrence County. He also collected a single relict (a weathered shell that has been dead a long period of time) specimen from Myatt Creek in Fulton County (John Harris, in litt. 1997). Comprehensive surveys have not been conducted in these rivers since 1996. The historical locality (near Shirley, Van Buren County, Arkansas) where a single scaleshell mussel specimen was collected from the Middle Fork of the Little Red River no longer provides mussel habitat. Clarke (1987) stated that suitable mussel habitat was restricted to a 9.6 km (6.0 mi) stretch from the confluence of Tick Creek upstream to the mouth of Meadow Creek. Arkansas River drainage (Oklahoma and Arkansas)--The scaleshell mussel has been collected from the following streams from the Arkansas River drainage: Poteau River in Oklahoma (Gordon 1991), Frog Bayou in Arkansas (Harris and Gordon 1987), and the South Fourche LaFave and Mulberry Rivers in Arkansas (Gordon 1991; Harris 1992). A single scaleshell mussel specimen was collected in the Poteau River (Gordon 1980). However, it has not been documented in subsequent surveys of this river (Branson 1984; Harris 1994). The existence of scaleshell mussels in Poteau River is doubtful. Gordon (1980) collected two scaleshell mussel specimens from Frog Bayou. Beaver Reservoir now inundates one of the Frog Bayou collection sites. The most recent collection was a fresh dead individual during a 1979 survey (Gordon 1980). Gordon noted that stream bank bulldozing upstream recently disturbed this site and other nearby sites. He also reported in-stream gravel mining activities at several sites. Within Frog Bayou, potential habitat is restricted to the area between Rudy and the confluence of the Arkansas River. Above Rudy, two reservoirs impact the river; one near Maddux Spring and the other at Mountainburg. Live mussels have not been found at the confluence of the Arkansas River, likely due to dredging activities (Gordon 1980). Although the current status of the scaleshell mussel in Frog Bayou is uncertain, any remaining individuals are in potential jeopardy due to limited habitat and in-stream mining activities. The only scaleshell mussel record from the South Fourche LaFave River is based on a single live specimen found in 1991 (Harris 1992). An 86-acre reservoir is approved for construction on Bear Creek approximately six miles upstream from this site. However, the effect of this impoundment on scaleshell mussels is uncertain. The potential for discovering additional scaleshell mussel sites in this river is unlikely due to the limited availability of suitable substrate. Similarly, other major tributaries of the South Fourche LaFave River provide little mussel habitat. Like Frog Bayou, the persistence of scaleshell mussels in this river is in doubt. Although Gordon (1991) reported scaleshell mussels from the Mulberry River, documentation is lacking. Recent surveys did not find the species in the Mulberry River (Craig Hilborne, U.S. Forest Service, pers. comm. 1995; [[Page 51327]] Stoeckel et al. 1995). The existence of scaleshell mussels in the Mulberry River is unlikely. Red River drainage (Oklahoma and Arkansas)--The scaleshell mussel has been documented from the following streams in the Red River drainage: the Kiamichi River, Gates Creek, Little River, Mountain Fork; and the Cossatot, Ouachita, Little Missouri, and Saline Rivers. Isley (1925) first collected scaleshell mussels from the Kiamichi River in 1925. Based on his account, the Kiamichi River historically supported a diverse and abundant mussel fauna. He collected 36 scaleshell mussel specimens at one of 22 stations visited. A single specimen was also collected from Gates Creek, a tributary of the Kiamichi River, by Valentine and Stansbery (1971). As recently as 1987, Clarke described the Kiamichi River as ``in remarkably good condition'' and a ``faunal treasure'' (Clarke 1987). However, despite extensive searches of the Kiamichi River over the last 11 years, only a single fresh dead shell of scaleshell mussel (in 1987) has been collected (Caryn Vaughn, Oklahoma Biological Survey, pers. comm. 1997; Charles Mather, University of Science and Arts of Oklahoma, in litt. 1984 and 1995). Vaughn (pers. comm. 1997) failed to find even a dead shell during three years (1993-1996) of surveys in the Red River Basin. However, the mussel habitat in the Kiamichi River is in relatively good condition above the Hugo Reservoir (Clarke 1987) and may still support a remnant population of scaleshell mussels. Although there is no evidence of scaleshell mussels persisting in the Little River, healthy mussel beds exist above the Pine Creek Reservoir (Caryn Vaughn, in litt. 1997). Below Pine Creek Reservoir, the mussel fauna is severely depleted but recovers with increasing distance from the impoundment (Caryn Vaughn, in litt. 1997). Although scaleshell mussels have not been documented during extensive surveys throughout the length of the Little River, suitable habitat remains and the species may persist (Caryn Vaughn, in litt. 1997). However, the discharge of reservoir water from Pine Creek and periodic discharge of pollution from Rolling Fork Creek may seriously impact any remaining viable scaleshell mussel populations and prohibit any future recolonization (Clarke 1987). Valentine and Stansbery (1971) reported a single specimen from Mountain Fork. Clarke (1987) hypothesized that, based on the presence of mussels at the confluence of Mountain Fork and beyond the Arkansas border, damage to Mountain Fork from the Broken Bow Reservoir has not occurred. However, Vaughn (in litt. 1997) indicated that these areas have been severely depleted with most no longer containing live mussels. If scaleshell mussels still occur in the Red River drainage in Oklahoma, extant populations are probably small and are likely restricted to isolated areas of suitable habitat in the Kiamichi and Mountain Fork Rivers. Given the extensive survey effort over the last decade, long-term survival of the scaleshell mussel in Oklahoma is doubtful. Harris collected single scaleshell mussel specimens from the Cossatot and Saline Rivers in Arkansas in 1983 (John Harris, in litt. 1997) and 1987 (John Harris, pers. comm. 1995), respectively. No other information is available for either river. The existence of scaleshell mussels in the Ouachita River and its two tributaries, the Saline River and Little Missouri River, is questionable as well. Both the Little Missouri and Saline Rivers records are based on single specimens. The Saline River specimen was collected in 1964 (Clarke 1996), and the Little Missouri River collection record is from 1995 (John Harris, in litt. 1997). Four undated museum specimens of scaleshell mussels from the Ouachita River in Arkadelphia, Clark County, Arkansas are listed in Clarke (1996), but details are unavailable. Based on the few collections and the limited habitat available, the long-term persistence of scaleshell mussel in Cossatot, Saline, Little Missouri, and Ouachita Rivers appears precarious. Lower Mississippi River Basin summary--Of these 21 rivers and tributaries in the lower Mississippi River Basin that historically supported scaleshell mussels, nine, and possibly an additional six, support the species today. Of these populations, the South Fork Spring River could possibly be stable; the St. Francis River, Kiamichi River, Little River, Mountain Fork, Spring River, Frog Bayou, South Fourche LaFave River, and White River are presumed to be declining; and the status of the Myatt and Gates Creeks and the Strawberry, Cossatot, Saline, and Little Missouri Rivers populations are unknown. Previous Federal Action We had identified the scaleshell mussel as a Category 2 candidate species in a notice of review published in the Federal Register on May 22, 1984 (49 FR 21664). The scaleshell mussel remained a Category 2 candidate species in subsequent notices including January 6, 1989 (54 FR 554), November 21, 1991 (56 FR 58804), and November 15, 1994 (59 FR 58982). Prior to 1996, a Category 2 candidate species was one that we were considering for possible addition to the Federal List of Endangered and Threatened Wildlife, but for which conclusive data on biological vulnerability and threats were not available to support a proposed rule. We discontinued designating Category 2 species in the February 28, 1996, Notice of Review (61 FR 7596). We now define a candidate species as a species for which we have on file sufficient information on biological vulnerability and threats to support issuance of a proposed rule. We designated the scaleshell mussel as a candidate species on October 16, 1998. On August 13, 1999 (64 FR 44171), we published a proposal to list the scaleshell mussel as an endangered species and opened a 60-day comment period on the proposal. On November 29, 1999 (64 FR 66600), we reopened the comment period for 39 days in order to hold a public hearing. The hearing was held in Jefferson City, Missouri, on December 8, 1999. Summary of Comments and Recommendations In the August 13, 1999, proposed rule, and through associated notifications, we requested all interested parties to submit factual reports or information that might contribute to the development of a final rule. We contacted appropriate Federal and State agencies, County governments, scientific organizations, and interested parties and requested their comments. We published notices inviting public comment in the following newspapers in 1999: The Chicago Sun Times, The Chicago Tribune, The Peoria Journal Star, State Journal-Register, The Journal Gazette Co., The Indianapolis Star, The Columbia Daily Tribune, The Kansas City Star, The St. Louis Post-Dispatch, The South Bend Tribune, The Cedar Rapids Gazette, Quad City Times, The Des Moines Register, The Cincinnati Post, The Cleveland Plain Dealer, The Columbus Dispatch, Cuba Free Press, Steelville Star-Crawford Mirror, Jefferson County Journal, Jefferson County Leader, Jefferson County News Democrat Journal, Meramec Journal, Jefferson County Watchman, TriCounty Journal, County Star Journal West, Chesterfield Journal, Clayton-St. Louis County Watchman, North County Journal-West, Florissant Valley Reporter, North County Journal-East, North Side Journal, County Star Journal-East, Concord Call, Mid-County Journal, Oakville Call, Oakville/Mehlville Journal, St. Louis Countian, South [[Page 51328]] County Journal, South County Times, Southwest County Journal, Webster- Kirkwood Times, West County Journal, Citizen Journal, Webster/Kirkwood Journal, South County News-Times, Press Journal, New Haven Leader, St. Clair Missourian, Sullivan Independent-News, Franklin County Watchman, Union Missourian, Washington Missourian, Bland Courier, Advertiser- Courier, Gasconade County Republican, Unterrified Democrat, Dixon Pilot, The Richland Mirror, Fort Leonard Wood Essayons, and The Daily Guide. The Service hosted a public hearing (December 8, 1999, in Jefferson City, Missouri) at the request of Two Rivers Levee and Drainage Association, Law Offices of John C. Franken, Howard/Cooper County Regional Port Authority, and 180 private citizens. To accommodate this request, we reopened the comment period from November 29, 1999, to January 7, 2000, to allow for consideration of, and to provide an opportunity for, further comments. A notice of the hearing and reopening of the comment period was published in the Federal Register on November 29, 1999 (64 FR 66600), and in legal notices in the newspapers listed above. We received 26 letters providing comments and information during the comment periods. Additionally, six individuals provided oral statements at the public hearing. We have updated this rule to reflect any changes in information concerning distribution, status, and threats since the publication of the proposed rule. All pertinent comments have been considered in the formulation of this final rule. Written comments received during the comment periods and written comments and oral statements presented at the public hearings are addressed in the following summary. Comments of a similar nature or point are grouped together (referred to as ``Issues'' for the purpose of this summary) below, along with the Service's response to each. Issue 1: One respondent was unsure of what this listing would accomplish beyond the recovery efforts of other mussel species already federally listed in Missouri. Response: This action will extend the Act's protection to this species. Federal listing results in an increased awareness of this species' status and its need for conservation attention. It also provides for opportunities for funding research, management activities, and conservation actions specifically targeted for this species. In addition to better funding opportunities, Federal endangered status encourages scientists and natural resource managers to focus research and conservation actions specifically for the scaleshell mussel. There are currently four federally listed mussel species in Missouri (Missouri Natural Heritage Database 1999). These are the pink mucket (Lampsilis abrupta), Curtis pearlymussel (Epioblasma florentina curtisi), Higgins' eye (Lampsilis higginsii), and fat pocketbook (Potamilus capax). We agree that where overlap of listed mussels occurs, the prohibitions of the Act will provide little additional protection of habitat. However, the current range of scaleshell mussel extends to areas where there are no federally listed species. The Act will provide protection from further habitat loss and degradation in these areas. Issue 2: One respondent was concerned that the public will not know what impacts this listing will have on activities on private property until after the recovery plan is completed. The respondent was referring to potential impacts of recovery actions on private land in particular. Response: While recovery plans are not developed until after a species is listed, there is opportunity for public input in the recovery planning stage. The purpose of the recovery plan is to set recovery objectives (goals) and identify the tasks needed to meet those objectives before a species can be downlisted or delisted. As the draft recovery plan is announced in the Federal Register, we will solicit comment from species experts, natural resource managers, and other interested parties. To ensure broad participation in the review of the recovery plan, we will notify all interested parties that were identified during the listing process (for example, those that provided comments or requested to be on our mailing list). Although actions that could be affected by the listing were identified in the proposed rule, we acknowledge that impact upon private actions cannot be fully assessed until a recovery plan is developed. However, in ascertaining whether a species warrants Federal protection under the Act, we may consider only biological factors. In accordance with 16 U.S.C. sec. 1533(b)(1)(A) and 50 CFR 424.11, listing decisions are made solely on the basis of the best scientific and commercial data available. The legislative history of the 1982 Act amendments states: ``The addition of the word ``solely'' is intended to remove from the process of the listing or delisting of species any factor not related to the biological status of the species. The Committee strongly believes that economic considerations have no relevance to determinations regarding the status of the species. * * *'' H.R. Rep. No. 567, Part I, 97th Congress, 2nd Session 20 (1982). Thus, the impact of listing on private activities, although of great interest and importance to the public, is not a factor we may consider in our listing determination. Issue 3: One respondent questioned whether the range of the scaleshell mussel, particularly in the Missouri River, is based on records that were identified correctly. Scaleshell mussels can be easily confused with the fragile papershell (Leptodea fragilis) or the pink papershell (Potamilus ohioensis), which are more common and widespread. Response: We acknowledge that scaleshell mussels may be confused with other species by the casual observer. Freshwater mussels are often difficult to identify by shell shape alone. However, to malacologists (a person who studies mollusks) and other properly trained biologists, there are no ambiguities in distinguishing scaleshell mussels from other species. Female scaleshell mussels are unique and unlikely to be mistaken with any other species. Females are small, very elongated, and the posterior edge is ruffled. Male scaleshell mussels can possibly be confused with other species, particularly the fragile papershell. However, several external characteristics distinguish male scaleshell mussels from the fragile papershell, the pink papershell, and other species. These characteristics include the presence of green rays, light brown periostracum, pointed posterior end, absence of dorsal wings, elongated shell, straight dorsal margin, and rounded ventral margin (Parmalee and Bogan 1998, Oesch 1995, Watters 1995). While it is possible that a small number of scaleshell mussel specimens have been misidentified, we are confident that the range of this species is based on valid specimens because many records are represented by voucher specimens that are housed in museums. The identification of these specimens has been verified by expert malacologists. In particular, the records of scaleshell mussel from the Missouri River were identified by Dr. David H. Stansbery, who is a leading authority in North America on freshwater mussel identification at the Ohio State Museum located at Ohio State University in Columbus, Ohio. Issue 4: The proposed rule states that gravel mining has recently become a more serious threat for scaleshell mussel range-wide because the Corps' authority to regulate instream gravel mining has been reduced. One respondent stated that this issue will probably not be [[Page 51329]] overlooked by the State agencies. In other words, gravel mining will probably be regulated by State agencies now that the Corps has less authority to regulate this activity. Response: Section 404 of the Clean Water Act of 1972 (CWA) provides regulations for discharge of dredged and fill materials in surface waters, including a permit program to ensure that such discharges comply with other State and Federal environmental regulations. The Corps is the Federal agency responsible for implementing this section of the CWA. Until 1997, instream mining was more strictly regulated, because incidental fallback of material during a dredging action was considered fill in surface waters, and thus triggered section 404 compliance. Due to a 1997 Federal court decision, however, incidental fallback of material is no longer considered fill. Consequently, only activities that result in discharge of fill material greater than incidental fallback are regulated under section 404 (see factors A and D under the ``Summary of Factors Affecting the Species'' section for further information on this issue). As discussed in Issue 1, federally listed species frequently coexist with scaleshell mussels. Section 7 of the Act requires all Federal agencies, including the Corps, to consult with the Service regarding any action that may adversely affect listed species. Through this consultation process, the Service identifies conservation measures, which minimize adverse impacts to listed species. With incidental fallback no longer requiring a Corps section 404 permit, the section 7 consultation process is no longer applicable for many instream gravel mining activities. Some State agencies have authority to regulate gravel mining within their state. In Arkansas, instream gravel mining is regulated by the Arkansas Open-Cut Mining and Land Reclamation Code, which contains guidelines to reduce impacts (Roell 1999). The Missouri Department of Natural Resources (MDNR) also has the authority to regulate gravel mining in Missouri under the Land Reclamation Act. However, their regulatory authority is limited. First, only commercial operators are required to obtain a permit to remove gravel from streams and rivers. City, county, and state operators using their own equipment and private operations are not required to obtain a permit from MDNR. Also, these operators are not obligated to comply with permit conditions that are crucial in avoiding adverse impacts to the stream environment. Second, MDNR's conditions for gravel mining permits are less stringent than those required previously by the Corps (Mike Larson, Missouri Department of Natural Resources, pers. comm. 2000). For example, the MDNR permit does not prohibit the modification of water conveyance, limit excavation to unconsolidated areas, require bank and water buffer strips, or minimize the removal of aquatic and terrestrial vegetation. All of these factors could adversely affect the scaleshell mussel and its habitat. Issue 5: Several respondents are concerned that this listing will impact activities on private property. One respondent was concerned that impoundments will be more difficult to construct after the listing. Response: This listing will protect scaleshell mussels from take under section 9 (Prohibited Acts) of the Act. Take is defined by the Act as ``harass, harm, pursue, hunt, shoot, wound, capture, collect, or attempt to engage in any such conduct.'' Take is further defined by regulation to include ``significant habitat modification or degradation that actually kills or injures wildlife,'' (50 CFR 17.3 ``Harm''). Non- Federal property owners, such as private landowners, corporations, or State or local governments, wishing to conduct activities on their land that might result in the incidental take of scaleshell mussels can obtain an incidental take permit from the U.S. Fish and Wildlife Service. Section 10 of the Act provides for the issuance of permits to conduct otherwise prohibited activities. Through section 10, there is an opportunity to provide species protection and habitat conservation for non-Federal development and land use activities that may result in incidental take of a listed species. For landowners and local governments, these incidental take permits, and their associated habitat conservation plans (HCP), provide long-term assurances that their activities will be in compliance with the requirements of the Act. Biologically, they provide the Service with a tool to offset the incidental take of listed species by reconciling species conservation with economic development. The HCP process allows private development to proceed while promoting listed species conservation. The No Surprises policy provides assurances to non-Federal landowners participating in HCP efforts through the section 10(a)(1)(B) process. Essentially, landowners are assured that if ``unforeseen circumstances'' arise, the Services will not require, without the consent of the permittee, the commitment of additional land, water or financial compensation or additional restrictions on the use of land, water, or other natural resources beyond the level otherwise agreed to in the HCP. The government will honor these assurances as long as a permittee is implementing the terms and conditions of the HCP, permit, and other associated documents in good faith. In effect, this regulation states that the government will honor its commitment as long as HCP permittees honor theirs. An activity on private land could also possibly be affected by this listing if that project (1) would need to be authorized, permitted, or funded by the Federal government, (2) would be located in habitat occupied by the scaleshell mussel or in designated critical habitat for the species, and (3) would have a direct or indirect effect on the species or its designated critical habitat. Federal programs and activities of this nature would usually require consultation with the Service under section 7 of the Act to evaluate the nature and extent of the adverse impacts and determine if project modification is necessary to reduce those impacts. Proposed impoundments within currently occupied streams and rivers are one type of activity that will require consultation. See the ``Available Conservation Measures'' section for additional examples of activities that will and will not require consultation. While certain activities may require consultation, projects are rarely terminated due to the presence of a federally listed species, and private landowners are usually not affected. The consultation process is the responsibility of the Federal agencies involved. The majority of section 7 consultations are resolved informally. For example, consultation is ended at an early stage if the potential impacts of a proposed project are expected to be discountable, insignificant, or beneficial to the species. Even if a significant adverse effect is expected, the consultation can usually be concluded by developing minor modifications to project plans or designs that avoid those impacts. If potential impacts are of such nature that a federally listed species is likely to be adversely affected and such effects cannot be removed, formal consultation would be required. However, section 7(b)(4) of the Act allows incidental take of the listed species resulting from Federal actions if such take is not likely to jeopardize the continued existence of the species and if reasonable and prudent measures are implemented to minimize the adverse impacts of such take. A General Accounting Office audit (1992), which found that 99.9 percent of all projects reviewed between 1988 and 1992 went [[Page 51330]] forward unchanged or with only minor modifications as a result of the section 7 consultation, attests to the regulatory flexibility afforded by the Act. Issue 6: One commenter stated that the same threats (i.e., water pollution, sedimentation, channelization, and impoundments) listed as impacting scaleshell mussel in the past (prior to 1950) are stated for present and future populations. The commenter stated that these conditions have improved. In Missouri, most of the channelization was established before the 1930s. Since 1950 land management practices have also evolved to more effectively control erosion and runoff, and the impacts of water pollution and sedimentation have been reduced. Response: The Service recognizes that some of these factors have improved, particularly land management practices to reduce erosion and runoff. In fact, the reason scaleshell mussels continue to persist could possibly be due to these improvements. However, the same threats that contributed to scaleshell mussels' decline before 1950, are still being observed and continue to impact scaleshell mussels. Channelization and new impoundments are currently proposed within the range of the scaleshell mussel, and water quality degradation and siltation has recently been documented as a serious threat in areas still occupied by scaleshell mussels. These threats are ongoing and qualify the scaleshell mussel for listing (See factor A in the ``Summary of Factors Affecting the Species'' section). The small number and low density of the remaining populations exacerbate threats and adverse effects of chance events on the species. Issue 7: The data cited in the notice of proposed listing provide inadequate support for listing the scaleshell mussel as an endangered species. The decline of the scaleshell mussel is not serious enough to warrant listing. The six potential additional populations (status unknown), which would increase the current number of populations by almost 50 percent, merit further investigation before the listing decision is made. Response: Under section 4(b)(1)(A) of the Act, a listing determination must be based solely on the best scientific and commercial data available regarding the species' biological status and threats to its existence. Endangered status is assigned to species which are in danger of extinction throughout all or significant portion of their range. A species may be determined to be an endangered or threatened species due to one or more of the five factors described in section 4(a)(1) of the Act. These factors include (1) the present or threatened destruction, modification, or curtailment of its habitat or range; (2) overutilization for commercial, recreational, scientific, or educational purposes; (3) disease or predation; (4) the inadequacy of existing regulatory mechanisms; and (5) other natural or manmade factors affecting its continued existence. The scaleshell mussel has undergone one of the most extensive range reductions of all the federally listed freshwater mussel species. It is considered extirpated from ten states and from 39 of the 55 rivers within its historical range. Although 14 populations, and possibly six others, persist, the long-term viability of these populations is threatened by a variety of ongoing threats (see ``Summary of Factors Affecting the Species'' discussion). Given the extent of range reduction that has occurred and the persistence of threats to the remaining populations, we believe the scaleshell mussel is in danger of extinction throughout a significant portion of its range. Issue 8: Detecting population changes by using available data for a rare species is speculative. Specifically, the proposed rule states that the long-term viability of scaleshell mussel populations in the Meramec basin is tenuous. In a recent survey on the Meramec River, more scaleshell mussels were found than in a past survey. The respondent did not understand how those data could support a conclusion that the species is declining. Response: The Service acknowledges that rare species are difficult to census, and thus, deriving population trends based on counts of individuals is difficult and sometimes impossible. It is a common problem in rare species conservation that, as numbers of a rare species continue to decline, it becomes increasingly difficult to find and count the individuals in order to ``prove'' the decline is continuing. However, reliable inferences on the status and long-term viability of individual populations, as well as for a species as a whole, can be made based on ecological principles, small population biology theory, and observations of threats and habitat loss from field investigations. For example, population stability implies that recruitment exceeds mortality. For freshwater mussels, the presence of juveniles serves as the best evidence for recruitment. Thus, failure to collect juvenile specimens suggests that the population is declining. Similarly, small populations are more susceptible to extinction due to chance events, such as disease, drought, accidental spills of contaminants, or other fluctuations in local environmental conditions. Thus, even without multiple years of survey data, we know that low density mussel populations are vulnerable. Small populations must also rely on movement of individuals among populations to remain genetically viable. Thus, mussel populations that are isolated are threatened. In addition to these biological factors, the presence of threats, regardless of population size, can substantially influence the conservation status of a population. Using these factors, the health of individual populations and the species can be determined. To ensure consistency and objectivity, Szymanski (1998) developed criteria based on the aforementioned factors to assign status and trend categories to each scaleshell mussel population. These criteria were utilized in the proposed rule. However, a discussion of status and trends using the same set of limited data was confusing and redundant to readers. Therefore, in this final rule, we devised a single classification system (i.e., combined status and trend categories) to assess population health (Table 1). The revised classification system differs only in the presentation of the data and the results of its application are similar to those derived from the Szymanski (1998) methodology. As a result of additional information that was obtained during the public comment period, the status or trends reported in the proposed rule for a few populations differs from those reported herein. For example, the status of the White River population changed from extirpated to presumed declining as new information documented a 1999 live scaleshell mussel collection from this river. A discussion of the criteria used for this classification system is provided in the ``Distribution and Abundance'' section. With respect to the recent survey work in the Meramec River, the greater number of scaleshell mussels found in the 1997 survey was likely due to two aspects of the survey, and not a result of a population increase (Roberts and Brunderman 2000). First, a special effort was made to collect this species (i.e., raking the top layer of the substrate by hand) because it often lies buried in the substrate. This method likely increased the probability of finding the species compared to past surveys. Second, lower water levels from drought conditions exposed a mussel bed at one site, causing scaleshell mussels to actively crawl on top of the substrate. The collection of only 19 scaleshell mussels, when viewed in light of the modified survey techniques and the [[Page 51331]] high visibility of individual mussels at one mussel bed, is strong evidence of the extreme rarity of this species. When attempting to monitor rare species, for which surveys usually locate only one or several surviving individuals, it is not uncommon for variations in survey methodology, weather conditions, and even time of day to affect the results of the survey. For species of extreme rarity, the effects of these factors can easily obscure the true population trend for the species. For this reason, we usually use criteria, in addition to population or density estimates, to evaluate the health of individual populations and the species as a whole. Based on the criteria described earlier, the three scaleshell mussel populations in the Meramec Basin (the Meramec, Bourbeuse, and Big Rivers) are believed to be declining at the present time. The long- term persistence of these populations is considered questionable because of marked habitat loss and other existing threats. Furthermore, the small number of individuals and low density of these populations exacerbate the magnitude and adverse impacts of threats (see ``Summary of Factors Affecting the Species''). Thus, despite the fact that more scaleshell mussels were collected from the Meramec River in a recent survey than in the past, other factors indicate that these populations are threatened and are declining. Issue 9: One respondent requested clarification of references to historical and existing distribution and abundance of scaleshell mussels. The respondent asked if the terms ``populations'' and ``occurrences'' are equivalent and if populations are equal in size and other qualities. Response: A ``historical record'' is any site where the scaleshell mussel has been documented regardless of when it was collected. The Service believes that recently discovered sites do not represent areas that have been colonized recently, but rather, they are sites that have existed historically (i.e., in historical times) and have not been previously known or sampled by collectors. A description of the historical range of the scaleshell mussel includes all known records. In contrast, a description of the existing distribution of the scaleshell mussel would include only its extant (that is, currently existing) range. An ``occurrence'' refers to a site where a scaleshell mussel specimen has been collected. An occurrence, which may be represented by one or more specimens, usually indicates the species is present or once existed in that area, depending on whether the specimen(s) is living or dead. In the context of this rule, the term ``population'' refers to all the current and historical occurrences of scaleshell mussels within a single river. It is impossible to determine if past and present scaleshell mussel populations are equal in size (in terms of number of individuals or length of stream inhabited), because many surveys conducted near the turn of the century were not thorough. However, it is believed that scaleshell mussels historically have always been rare relative to many other mussel species. Inferences regarding population trend can be made from existing data (e.g., age-structure, historical vs. current collections, habitat availability and condition, and threats). For example, scaleshell mussels were locally abundant in the Kiamichi River in the past (with 36 specimens collected from one sampling station). Today, however, no living scaleshell mussel specimens and only 1 fresh dead specimen were found during exhaustive survey efforts. It is apparent that scaleshell mussels, although always rare, occur today at lower densities than in the past in the Kiamichi River (see Issue 8 for further discussion regarding assessing conservation status). Within this final rule, populations that were assigned to the same conservation status do not necessarily have similar population size (although all populations persist at very low densities) or habitat quality. Issue 10: The proposed rule states that scaleshell mussels have not been found in the Upper Mississippi River basin in over 50 years. One respondent asked how often sampling has been conducted in the Upper Mississippi River basin, and what is the likelihood of detecting a locally rare species. Response: The historical range of the scaleshell mussel in the Upper Mississippi River basin includes the states of Illinois, Iowa, Minnesota, and Wisconsin. Natural resource agencies in these states are confident enough to consider the scaleshell mussel extirpated since it has not been collected in over 50 years despite a considerable number of surveys. Rivers with documented scaleshell mussel occurrences in the Upper Mississippi River basin include the Mississippi, Minnesota, Iowa, Cedar, Illinois, Sangamon, and Pecatonica Rivers, and Burdett's Slough of the Mississippi River (see ``Distribution and Abundance''). All of these rivers have been surveyed in the last 10-15 years. Surveys considered here are formal mussel surveys published in technical reports and scientific journals. Numerous other surveys, which are not discussed here, also have been conducted in these streams at selected sites for various Federal projects (e.g., proposed bridges, pipelines, channelization, etc.). Surveys have been conducted on the Minnesota River in 1977 and 1999 (Marian Havlik, Malacological Consultants, in litt. 2000; Tim Yager, Corps, St. Paul District, in litt. 2000). The Mississippi River mainstem, in particular, has been surveyed extensively since 1950. The Illinois, Sanagamon, and Pecatonica Rivers have also been surveyed extensively in the last 15 years (Kevin Cummings, pers. comm. 2000). The likelihood of detecting a locally rare species depends on the amount of time spent searching and the search methods employed. The most common method used for surveys is timed searches, which produce a measurement of the number of mussels collected per unit of time spent searching. Timed searches produce the most complete list of species (including rare species) at a given site (Strayer et al. 1997, Vaughn et al. 1997). Furthermore, the deficiency of suitable mussel habitat, both in quality and quantity, remaining in this drainage also suggest that scaleshell mussel persistence is highly unlikely. This is not to say individuals may not persist in the Upper Mississippi River drainage, but that the best available scientific information indicates that population viability is doubtful. Issue 11: One respondent believes that water turbulence produced by jet boat motors may be adversely affecting scaleshell mussels and other freshwater mussels in the Meramec River in Missouri. Response: The Service recognizes that jet boats, which can produce powerful water turbulence, could potentially have adverse affects on freshwater mussels including scaleshell mussels. Jet wash from motors may contribute to substrate destabilization and/or could dislodge adult and juvenile mussels from suitable habitat, particularly from shallow riffles where mussels typically occur. The magnitude and extent to which this factor may threaten populations, however, is unknown. Peer Review In accordance with our July 1, 1994, Interagency Policy on Peer Review (59 FR 34270) we requested the expert opinions of independent specialists regarding pertinent scientific or commercial data and assumptions relating to the supportive biological and ecological information in the proposed rule. The purpose of such review is to [[Page 51332]] ensure that the listing decision is based on scientifically sound data, assumptions, and analyses, including input of appropriate experts and specialists. We requested a formal scientific peer review from four malacologists who possess expertise on the scaleshell mussel. We received a written response and comments from two of these experts within the open comment periods. These experts strongly supported the listing proposal and agreed with the Service that this species is in need of Federal protection as an endangered species. One reviewer stated that the Service was thorough in reviewing this species and that the status and threats are accurately described. This reviewer felt that the threats posed by the zebra mussel to the scaleshell mussel, as discussed in the proposed rule, should not be underestimated. Additionally, more information was provided in one response regarding the extant distribution of the scaleshell mussel and threats to its existence. That information is incorporated into this final rule. Summary of Factors Affecting the Species After a thorough review and consideration of all information available, we determine that the scaleshell mussel should be classified as an endangered species. We followed the procedures found at section 4(a)(1) of the Act (16 U.S.C. 1531 et seq.) and regulations (50 CFR part 424) implementing the listing provisions of the Act. We may determine a species to be endangered or threatened due to one or more of the five factors described in section 4(a)(1). These factors and their application to the scaleshell mussel (Leptodea leptodon) are as follows: A. The Present or Threatened Destruction, Modification, or Curtailment of its Habitat or Range. Arguably, the scaleshell mussel has suffered a greater range reduction than any other unionid. The range of this species was once expansive, spanning the Mississippi River Basin in at least 55 rivers in 13 states (Szymanski 1998). Today, the range is significantly reduced with known extant populations persisting in only 14, potentially 20, rivers in three states. The scaleshell mussel has been eliminated from the entire upper and most of the middle Mississippi River drainages. Although much of the decline occurred before 1950, population declines continue in most portions of the species' range, and numerous threats are impacting the few remaining extant populations. Water pollution, sedimentation, channelization, sand and gravel mining, dredging, and impoundments contribute to the decline of the scaleshell mussel throughout its range and continue to affect existing populations. A general description of how these factors affect mussels is given below, followed by specific examples of how these threats are affecting scaleshell mussels in its extant range. Refer to Szymanski (1998) for a more detailed discussion of threats to freshwater mussels. Mussel biologists generally agree that contaminants are partially responsible for the decline of mussels (Havlik and Marking 1987, Williams et al. 1993, Biggins et al. 1996). Mussels are sedentary filter feeders and are vulnerable to contaminants that are dissolved in water, associated with suspended particles, or deposited in bottom sediments (Naimo et al. 1992). Contaminants enter streams from point and nonpoint sources. Point source pollution is the entry of material from a discrete, identifiable source such as industrial effluents, sewage treatment plants, and solid waste disposal sites. Freshwater mussel mortality from toxic spills and polluted water is well documented (Ortmann 1909, Baker 1928, Cairns et al. 1971, Goudreau et al. 1988). Decline and elimination of populations may be due to acute and chronic toxic effects that result in direct mortality, reduced reproductive success, or compromised health of the animal or host fish. Nonpoint source pollution is the entry of material into the environment from a diffuse source such as runoff from cultivated fields, pastures, private wastewater effluents, agricultural feed-lots and poultry houses, active and abandoned mines, construction, and highway and road drainage. Stream discharge from these sources may accelerate eutrophication (i.e., organic enrichment), decrease oxygen concentration, increase acidity and conductivity, and cause other changes in water chemistry that are detrimental to the survival of most mussel species and may impact host fishes (Goudreau et al. 1988, Dance 1981, Fuller 1974). Sediment is material that is suspended in the water, and is being transported, or has been moved, as the result of erosion (USSCS 1988). Although sedimentation is a natural process, agricultural encroachment, channelization, impoundments, timber harvesting within riparian zones, heavy recreational use, urbanization, and other land use activities can accelerate erosion (Waters 1995, Myers et al. 1985, Chesters and Schierow 1985). The water quality impacts caused by sedimentation are numerous. Generally, it affects aquatic biota by altering the substratum and by altering the chemical and physical composition of the water (Ellis 1936, Myers et al. 1985, USSCS 1988). Sedimentation directly affects freshwater mussel survival by interfering with respiration and feeding. Due to their difficulty in escaping smothering conditions (Imlay 1972, Aldridge et al. 1987), a sudden or slow blanketing of stream bottom with sediment can suffocate freshwater mussels (Ellis 1936). Sediment particles may carry contaminants toxic to mussels (Naimo et al. 1992). Increased sediment levels may also reduce feeding efficiency (Ellis 1936), which can lead to decreased growth and survival (Bayne et al. 1981). Channelization, sand and gravel mining, and dredging operations physically remove mussels from the water and may also bury or crush mussels (Watters 1995). Other effects of these activities extend upstream and downstream of the excavated area. Headcutting, the upstream progression of stream bed destabilization and accelerated bank erosion, can affect an area much larger than the dredging site (Hartfield 1993). In severe cases, this erosional process can extend for several miles upstream. As relatively immobile bottom-dwelling invertebrates, mussels are particularly vulnerable to channel degradation (Hartfield 1993). Accelerated erosion also releases sediment and pollutants, and in some instances, diminishes mussel diversity and habitat as documented in the Yellow and Kankakee Rivers in Indiana, the Big Vermillion River in Illinois, and the Ohio River (Fuller 1974). Gravel mining has recently become a more serious threat for scaleshell mussels range-wide. In 1997, a court ruling changed the interpretation of the CWA as it applies to the regulation of gravel mining (Roell 1999). Previously, gravel mining was more strictly regulated because ``incidental fallback'' (the incidental soil movement from excavation, such as the soil that is disturbed when dirt is shoveled, or back-spill that comes off a bucket and falls into the same place from which it was removed) was considered fill in surface waters, thus triggering section 404 of the CWA and the permitting process of the Corps. Prior to the 1997 ruling, gravel mining operators were required to obtain a Corps section 404 permit and follow several conditions outlined on the permit. Except in very small tributaries, the Corps required all operators to establish a streamside and riparian buffer and prohibited removing gravel from flowing water (i.e., no in- stream mining) or from below the water [[Page 51333]] table (Danny McKlendon, Corps, St. Louis District, pers. comm. 1998). These requirements avoided most adverse effects to mussels including headcutting, channel modification, and the physical crushing or removal of mussels. Furthermore, the Corps' permit process included consultation with the Service concerning the presence of federally listed species at each proposed mining site. However, the 1997 ruling eliminated the Corps authority to regulate most instream gravel mining activities, thereby eliminating the section 404 permit and the conditions that protected mussel beds. Therefore, the scaleshell mussel has lost much of its protection from gravel mining. Only activities resulting in discharge of fill material greater than incidental fallback (such as instream gravel stockpiling, stream crossings, and select removal methods) are regulated. However, many gravel mining operations may not fall under this category. Impoundments negatively affect mussels both upstream and downstream by inducing scouring, changing water temperature regimes, and altering habitat, food, and fish host availability (Caryn Vaughn, in litt. 1997). Impoundments permanently flood stream channels and eliminate flowing water that is essential habitat for most unionids, including scaleshell mussels (Fuller 1974, Oesch 1995). Scouring is a major cause of mussel mortality below dams (Layzer et al. 1993). Most detrimental, however, is the disruption of reproductive processes. Impoundments interfere with movement of host fishes, alter fish host assemblages, and isolate mussel beds from each other and from host fishes (Stansbery 1973, Fuller 1974, Vaughn 1993, Williams et al. 1993). The result is diminished recruitment (Layzer et al. 1993). Dams are effective barriers to fish host movement and migration that unionids depend on for dispersal. Mussels living upstream from the dam can become reproductively isolated from those living downstream causing a decrease in genetic diversity. Even small, lowhead dams can hinder fish movement and isolate mussel beds from fish hosts and from each other. For example, Watters (1996) determined that the upstream distribution of two mussel species, the fragile papershell (Leptodea fragilis) and pink heelsplitter (Potamilus alatus) stopped at lowhead dams. These species, like the scaleshell mussel, are believed to use the freshwater drum as a sole host. The same threats that caused the extirpation of historical populations of scaleshell mussel still exist and continue to threaten extant populations. This species appears to be especially susceptible to contamination and sedimentation. Historically, the species was widespread and occurred in diverse habitats. Today, scaleshell mussels no longer occur at disturbed sites that still support other endangered unionids (Szymanski 1998). This suggests that scaleshell mussels are especially sensitive to degraded water quality. Given the pervasiveness of the sources of pollution and sedimentation, it is apparent that these threats continue to be problematic for the remaining scaleshell mussel populations. Upper Mississippi River Basin The scaleshell mussel formerly occurred in eight rivers and tributaries within the Upper Mississippi Basin. However, this species has not been found in more than 50 years and is believed extirpated from this region (Kevin Cummings, in litt. 1994). We believe the same factors that have caused declines and extirpations of other mussel species including impoundments, pollution, sedimentation, and channelization and dredging activities, have caused the disappearance of scaleshell mussels from the Upper Mississippi River Basin. Middle Mississippi River Basin Similar to the Upper Mississippi River Basin, impoundments, pollution, sedimentation, and channelization and dredging activities are believed to have led to the extirpation of the scaleshell mussel from the entire Ohio River Basin. These same threats continue to adversely affect extant populations in the middle Mississippi River Basin. Scaleshell mussel habitat in the Meramec River Basin has been reduced in recent years. In 1979, Buchanan found living or dead scaleshell mussels in the lower 180 km (112 mi) of the Meramec River (Buchanan 1980). In 1997, living or dead scaleshell mussels were collected only in the lower 96 km (60 mi) of the river (Roberts and Bruenderman 2000). While portions of the lower reach continue to provide suitable habitat, mussel species diversity and abundance above mile 60 have declined noticeably in the last 20 years and 9 mussel beds are no longer present between river mile 21.5 and 145.7. Roberts and Bruenderman (2000) attributed this decline primarily to the loss of channel stability. Within the Meramec Basin, the Bourbeuse River has undergone the greatest change with respect to mussel populations. In particular, mussel populations have declined in the lower river. Whereas Buchanan (1980) found this section of the Bourbeuse River to have the greatest mussel diversity, this stretch was nearly devoid of mussels when resurveyed in 1997. Additionally, five mussel beds are no longer present between miles 0.4 and 137. Buchanan (in litt. 1997) and Roberts and Bruenderman (2000) attributed this decline to habitat loss from sedimentation, eutrophication, and substrate destabilization. The Big River has the lowest species diversity and abundance in the Meramec River Basin. Buchanan (1980) attributed this to the effects of lead and barite mining. While most mining operations have ceased, 45 dams retaining mine waste and numerous waste piles remain in the Big River Basin. Most of those dams were improperly constructed or maintained. The Corps found that only one of the 45 dams was safe and 27 received the worst possible rating and could fail during a flood. The poor condition of the dams has led to large influxes of mine waste into the Big River from dam collapse (MDC 1997). For example, since 1978, a ruptured tailings dam has discharged 63,000 cubic meters (81,000 cubic yards) of mine tailings into the Big River covering 40 km (25 mi) of stream bottom and negatively impacting the lower 129 km (80 mi) of the river (Alan Buchanan, in litt. 1995), making it less suitable for mussels. While no major impoundments exist in the Meramec River Basin, several old mill dams (low-head dams) affect the mainstem of the Big and Bourbeuse Rivers. Five dams are still in place along the lower 48 km (30 mi) of the Big River, and one dam exists in the lower Bourbeuse River. These structures are barriers to host fish movement during normal flows (MDC 1997) and thus, continue to depress reproductive rates of scaleshell and other mussels. Gravel mining poses an imminent threat to scaleshell mussel populations in the Meramec River Basin due to the high, and increasing, level of interest in gravel mining in the basin (Roberts and Brunderman 2000). For example, between 1994 and 1998, the Corps issued permits for 230 sites. Additional sites were mined without a permit, but the number of these unauthorized operations is unknown. (Danny McKlendon, Corps, St. Louis District, in litt. 1998). In 1994, several areas of the Gasconade River channel were highly unstable, possibly a result of riparian vegetation removal in conjunction with the 1993 flood. These areas had high cut mud banks with trees fallen into the river, unstable substrate, and contained very few mussels. Buchanan (1994) predicted that habitat degradation on this river would continue and [[Page 51334]] postulated that the mussel fauna would be further impacted with some species possibly disappearing. He noted that below river mile 6, only one stable gravel bar contained a diverse mussel fauna. High silt deposition from the Missouri River prohibits the formation of mussel habitat below this area. The majority of the Osage River system has been impounded and is no longer suitable for freshwater mussels. The majority of remaining mussel habitat occurs below Bagnell dam in the lower 80 miles of the Osage River proper. This river reach is affected by the operation of Bagnell dam, which alters flow and temperature regimes, lowers dissolved oxygen levels, and causes channel scouring and accelerated bank erosion. Several instream gravel mining operations currently exist in the Osage River that physically remove mussels from the water and cause headcutting and siltation. Lower Mississippi River Basin Channelization, levee construction, diversion ditches, control structures, and floodways have drastically altered much of the St. Francis River from the mouth above Helena, Arkansas, to Wa the St.