Daily Rules, Proposed Rules, and Notices of the Federal Government
This document consists of: (1) A final rule to list the Alabama pearlshell (
It is our intent to discuss in this final rule only those topics directly relevant to the listing and designation of critical habitat for the Alabama pearlshell, round ebonyshell, southern kidneyshell, Choctaw bean, tapered pigtoe, narrow pigtoe, southern sandshell, and fuzzy pigtoe under the Act (16 U.S.C. 1531
On October 4, 2011, we published the proposed rule to list and designate critical habitat for these eight mussels (76 FR 61482). Federal actions for these species prior to October 4, 2011, are outlined in the proposed rule. Publication of the proposed rule opened a 60-day comment period, which closed on December 5, 2011. On March 27, 2012 (77 FR 18173), we reopened the comment period for 30 days, from March 27 through April 26, 2012, in order to announce the availability of and receive comments on a draft economic analysis, and to extend the comment period on the proposed listing and critical habitat designation.
North American freshwater mussel fauna is the richest in the world and historically numbered around 300 species (Williams
These eight species are all freshwater bivalve mussels of the families Margaritiferidae and Unionidae. The Alabama pearlshell is a member of the family Margaritiferidae, while the round ebonyshell, southern kidneyshell, Choctaw bean, tapered pigtoe, narrow pigtoe, southern sandshell, and fuzzy pigtoe belong to the family Unionidae. These mussels are endemic to (found only in) portions of three Coastal Plain rivers that drain south-central and southeastern Alabama and northwestern Florida: the Escambia (known as the Escambia River in Florida and the Conecuh River in Alabama), the Yellow, and the Choctawhatchee. All three rivers originate in Alabama and flow across the Florida panhandle before emptying into the Gulf of Mexico, and are entirely contained within the East Gulf Coastal Plain Physiographic Region. The Alabama pearlshell is also known from three locations in the Mobile River Basin; however, only one of those is considered to be currently occupied.
Freshwater mussels generally live embedded in the bottom of rivers, streams, and other bodies of water. They siphon water into their shells and across four gills that are specialized for respiration and food collection. Food items include detritus (disintegrated organic debris), algae, diatoms, and bacteria (Strayer
Sexes in margaritiferid and unionid mussels are usually separate. Males release sperm into the water column, which females take in through their siphons during feeding and respiration. Fertilization takes place inside the shell. The eggs are retained in the gills of the female until they develop into mature larvae called glochidia. The glochidia of most freshwater mussel species, including all eight species addressed in this rule, have a parasitic stage during which they must attach to the gills, fins, or skin of a fish to transform into a juvenile mussel. Depending on the mussel species, females release glochidia either separately, in masses known as conglutinates, or in one large mass known as a superconglutinate. The duration of the parasitic stage varies by mussel species, water temperature, and perhaps host fish species. When the transformation is complete, the juvenile mussels drop from their fish host and sink to the stream bottom where, given suitable conditions, they grow and mature into adults.
Recent distributions are based on surveys conducted from 1995 to 2012. Historical distributions are based on collections made prior to 1995. Historical distribution data from museum records and surveys dated between the late 1800s and 1994 are sparse, and most of these species were more than likely present throughout their respective river basins. Knowledge of historical and current distribution and abundance data were summarized from Butler 1989; Williams
Assessing the state of a freshwater mussel population is challenging. We looked at trends in distribution (range) by comparing recent occurrence data to historical data, and we examined recent abundance (numbers). One difficulty of investigating population trends over time in these species is the lack of historical collection data within the drainages. Athearn (1964, p. 134) noted the streams of western Florida were inadequately sampled, particularly the lower Choctawhatchee, Yellow, and the lower Escambia Rivers. Blalock-Herod
Another difficulty is the lack basic information for some historical collections, including specific locality, total number of species or individuals collected, or collection date. For these reasons, the only accurate comparison that can be made of so many different sources of historical and recent collection data is whether a particular species was detected (present) or not (absent) during the survey. When examining occurrence data, we considered sampled areas in close proximity as the same sight. Generally, areas sampled that are within 2 river km (1.2 mi) (approximately) of each other are considered the same site, and sampled areas that are more than 2 km apart are considered different sites. Occurences are based on live animals and shell material. The occurrence data we examined using GIS mapping software. A summary historical and recent occurrence data, and current abundance is presented in Table 1.
We also considered each species' relative abundance in comparison to other mussel species with which they co-occur. In addition, we relied on various published documents whose authors are considered experts on these species. These publications either described the status of these species or assigned a conservation ranking, and include Williams
Most of the eight species have experienced a decline in populations and numbers of individuals within populations, but not all have experienced a decline in range. Recent, targeted surveys for the Alabama pearlshell and southern kidneyshell show a dramatic decline in historical range. The Choctaw bean, narrow pigtoe, fuzzy pigtoe, southern sandshell, and tapered pigtoe still occur in much of their historical range; however, they no longer occur at many locations at which they were historically known, and their numbers appear to be declining. The round ebonyshell's current range is larger than its historical range, but this is attributed to the use of dive equipment in recent surveys that allowed access to the species' deep, main channel habitat. Despite this range extension, the species still has a very limited distribution and is considered to be extremely rare.
The Alabama pearlshell (
The Alabama pearlshell is one of five North American species in the family Margaritiferidae. The family is represented by only two genera,
The Alabama pearlshell typically inhabits small headwater streams with mixed sand and gravel substrates, occasionally in sandy mud, with slow to moderate current. Very little is known about the life-history requirements of this species. However, Shelton (1995, p. 5 unpub. report) suggests that the Alabama pearlshell, as opposed to the Louisiana pearlshell, which occurs in large colonies, typically occurs in low numbers. The Alabama pearlshell is also believed to occur in male-female pairs. Of the 68 Alabama pearlshell observed by Shelton (1995, p. 5 unpub. report), 85 percent occurred in pairs. Males were always located upstream of the females and were typically not more than 1 meter (m) apart, and juveniles were usually found just a few inches apart. The species is believed to be a long-term brooder, where gravid females have been observed in December. The host fish and other aspects of its life history are currently unknown.
Historically, the Alabama pearlshell occurred in portions of the Escambia River drainage, and has also been reported from two systems in the Alabama River drainage. The Alabama pearlshell's known historical and current occurrences, by water body and county, are shown in Table 2 below.
The Amos Mill population, discovered in 2010, represents a new record, and possibly the only known surviving population in the Sepulga River drainage. The Burnt Corn and Otter Creek populations reaffirm historical records that had not been reported in nearly 30 years. Two of the Sandy Creek locations, discovered in 2011, are new populations. Since the late 1990s, more than 70 locations within the Alabama River Basin were surveyed for mollusks (McGregor
Recent data suggest that, of the nine remaining populations, the largest may occur in Little Cedar and Otter Mill creeks. In 2011, Fobian and Pritchett reported new populations at two locations in an unnamed tributary to Sandy Creek. Although this is not the first report from the Sandy Creek basin, it is the first for the two unnamed tributaries. In 2010, Buntin and Fobian (2011 pers. comm.) reported 10 live individuals from Otter Creek. This is the first time since 1981 that the pearlshell has been reported from this drainage. Also in 2010, Powell and Ford reported three live individuals, and several relic shells, from Amos Mill Creek, in Escambia County, AL. This is the first report of the pearlshell from this drainage, and county, and the first live individual from the Sepulga River system in nearly 50 years. Little Cedar Creek supported good numbers of Alabama pearlshell in the late 1990's (54 individuals reported in 1998). However, during a qualitative search of the same area in 2005, only two live pearlshell were found (Powell 2005 pers. obs.), and in 2006, three live pearlshells were observed (Johnson 2006 in litt.). Live Alabama pearlshell have not been observed in Hunter Creek since 1998, when eight live individuals were reported (Shelton 1999 in litt.). During two visits to the stream in 1999, Shelton found no evidence of the species (Shelton 1999
Evidence suggests that much of the rangewide decline of this species has occurred within the past few decades. Specific causes of the decline and disappearance of the Alabama pearlshell from historical stream localities are unknown. However, they are likely related to past and present land use patterns. Many of the small streams historically inhabited by the Alabama pearlshell are impacted to various degrees by nonpoint-source pollution.
The round ebonyshell (
Very little is known about the habitat requirements or life history of the round ebonyshell. It occurs in small to medium rivers, typically in stable substrates of sand, small gravel, or sandy mud in slow to moderate current. It is believed to be a short-term brooder, and gravid females have been observed in the spring and summer. The fish host(s) for the round ebonyshell is currently unknown (Williams
The round ebonyshell is known only from the main channel of the Escambia-Conecuh River and is the only mussel species endemic to the drainage (Williams
The round ebonyshell has a very restricted distribution (Williams and Butler 1994, p. 61), with its current range (based on live individuals and shell material) confined to approximately 144 km (89 mi) of the Escambia-Conecuh River main channel. The round ebonyshell is also considered to be extremely rare (Williams
The southern kidneyshell (
Very little is known about the habitat requirements or life history of the southern kidneyshell. It is typically found in medium creeks to small rivers in firm sand substrates with slow to moderate current (Williams
The southern kidneyshell is endemic to the Escambia, Choctawhatchee, and Yellow River drainages in Alabama and Florida (Williams
Since 1995, the southern kidneyshell has been detected at only 10 locations within the Choctawhatchee River drainage. The species appears to have been common historically (in 1964, H. D. Athearn collected 98 individuals at one site on the West Fork Choctawhatchee), but it is currently considered one of the most imperiled species in the United States (Blalock-Herod
The Choctaw bean (
Very little is known about the habitat requirements or life history of the Choctaw bean. It is found in medium creeks to medium rivers in stable substrates of silty sand to sandy clay with moderate current. It is believed to be a long-term brooder, with females gravid from late summer or autumn to the following summer. Its fish host is currently unknown (Williams
The Choctaw bean is known from the Escambia, Yellow, and Choctawhatchee River drainages in Alabama and Florida (Williams
The Choctaw bean persists in most of its historic range. However, it has experienced localized extirpations and its numbers are low, particularly in the Escambia and Yellow river drainages. Of 7 historical sites known to support the species within the Escambia River drainage, 1 location currently supports the species. Also, its numbers within the drainage are very low; a total of 14 individuals have been collected since 1995. Within the Yellow River drainage, the Choctaw bean is currently known from 4 locations which yielded 15 individuals total. In the Choctawhatchee River drainage, 3 of 10 historical sites examined recently continue to support the species. The Choctaw bean continues to persist in most areas and is currently known from a total of 37 locations throughout the drainage.
Heard (1975, p. 17) assessed the status of the Choctaw bean in 1975 and stated that it was formerly abundant in the main channel of the Choctawhatchee River in Florida, but has become quite rare. McGregor (2004, p. 103) considered the Choctaw bean vulnerable to extinction due to its limited distribution and habitat degradation, and classified it as a species of high conservation concern in Alabama. Williams
The tapered pigtoe (
The tapered pigtoe is found in medium creeks to medium rivers in stable substrates of sand, small gravel, or sandy mud, with slow to moderate current (Williams
The tapered pigtoe is endemic to the Choctawhatchee River drainage in Alabama and Florida (Williams
The tapered pigtoe appears to be absent from portions of its historic range and found only in isolated locations (Blalock-Herod