Arcidens wheeleri

Inoue et al. (2014) determined that the genus Arcidens has priority over Arkansia, thus arguing for the acceptance of this species' name as Arcidens wheeleri (accepted as such by Williams et al. 2017).

There is but one viable population of this species. Three to four other populations, all highly isolated, are known to still be extant. The current range extent is at most <12,000 km² with an area of occupancy for 5-9 1-km2 grid cells; a loss of a least half of but perhaps as high as 87% of the species’ historical range. Historical declines in population numbers and loss of viability have been documented. IUCN considers the species’ population trend to be declining. Threats are persistent and at a high to very high level.

The species is currently known primarily from the Kiamichi River but small populations are also found in the Little and Ouachita Rivers, in Oklahoma and Arkansas. The current status of purported populations in Pine and Sanders Creeks in Texas (records from early 1990s) is unknown. Cummings and Cordeiro (2011), in their IUCN assessment, estimated the species’ current range extent as 1000–5000 km². Data from NatureServe plots at 11,891 km² using records from 1993 to 2013 or at 3369 km² if just plotting records from 2002-2013. Historically, the species is thought to have occupied an area >25,000 km²; indicating a 53-87% loss in the species’ range.

Information is largely derived from USFWS (2004): The small, closely situated Red River tributary portions likely are incompletely isolated from each other (in terms of larval dispersal between populations), and are regarded here as parts of a single area of occurrence, i.e., inhabited by a single metapopulation. The four major areas are as follows: the species still occurs in the Ouachita River in Arkansas (Harris and Gordon, 1987; Posey et al., 1996), but in very low abundance; it occurs in the Kiamichi River; Gordon and Harris (1983) collected relict shells from the Little River in Arkansas and Clarke (1987) found a small number in a 1-km reach of the Little River while in the Arkansas portion, Vaughn et al. (1995) found an A. wheeleri shell east of the Oklahoma-Arkansas state line in 1994; Mather (pers. comm. 1993, in litt. 2001) and Bergmann found shells in the Little River, McCurtain Co., Oklahoma, in 1991. Follow-up surveys in 1992 and 1993 produced additional shells (Vaughn, 1994, Mather, in litt. 2001). Although most Oklahoma shells were weathered, one collected in 1991 and 1993 appeared to have died recently. In 1994, Vaughn et al. (1995) discovered living A. wheeleri in the Little River, McCurtain Co.; also relict shells downstream in Oklahoma and Arkansas. It was recently found in the Little River, Oklahoma (Vaughn and Taylor, 1999). Vaughn (2000) cites occurrences in the Kiamichi River in Oklahoma. All recent records suggest the species exhibits a range of approximately 153 km in the Little River. However, significant parts of that range are unsuitable, thus 111 km is more accurate but high quality prevails in only a limited section (24 km) upstream of the Mountain Fork River confluence. In 1992, Bergman found a shell in Pine Creek, Lamar Co., Texas (Mather pers. comm., 1993; Howells et al.. 1996; 1997); and a second specimen in Sanders Creek in 1993. Galbraith et al. (2008) summarized the current status in southeastern Oklahoma as the Kiamichi River (3 spms. from one site in Moyers, relict shell south of Clayton, a live specimen from 1993 upstream of Rattan), Little River (one site in 1990s but not recently, 2 live at another site above Mountain Fork River confluence).

Information is largely derived from USFWS (2004):
Impoundment, channelization, and water quality degradation have been identified as principal factors causing the decline of the Ouachita rock pocketbook (Clarke, 1987; Mehlhop and Miller, 1989; Martinez and Jahrsdoerfer, 1991). As highly influential factors, impoundment, channelization, and water quality degradation are recognized as major modifications that embrace many smaller modifications and reactions. Commonly observed evidence of effects in actual environments include reduced communities of only tolerant species, dead mussels or shells positioned naturally in the substrate, or populations containing no or reduced numbers of juvenile mussels. Continued growth and activity of human populations portend that these major factors, at least impoundment construction and water quality degradation, will continue and expand in influence. Within portions of this species' range, recent proposals to withdraw and transport large quantities of water for human consumption have raised an additional threat, related essentially to reservoir development, and with similar bearings on stream organisms. Moreover, various other factors, mostly secondary in significance, have been identified as potential future threats to A. wheeleri.

Specific details of generalized threats are outlined in USFWS (2004) under the following threat categories: impoundment, channelization, and flow modification; water quality degradation; other factors (gravel excavation, construction of road and utility crossings, and vehicle/livestock activities; changes in landscape condition and introduction of unmitigated human activities; the introduced Asian clam, Corbicula. fluminea, and exotic zebra mussel, Dreissena polymorpha, which is not yet sympatric with Arkansia wheeleri; accidental harvest).