Truncilla macrodon

The species is endemic to Texas and has, historically and currently, a small geographic range. It has been extirpated from perhaps as much as 85% of its historic range. There are 2-3 viable populations. The overall population “may already be below the minimum viable population requirement,” as per USFWS’ (2016) assessment. Threats are considered very high and imminent and are “likely to result in the extinction of the Texas Fawnsfoot in the foreseeable future” (USFWS 2016).

This species is currently known from portions of the Brazos, Colorado, and San Saba Rivers. Isolated/remnant populations appear to persist in the Clear Fork Brazos River and Deer Creek. Reports from the Trinity River are considered to actually be of Truncilla donaciformis (USFWS 2015). The species is not known from Oklahoma.

USFWS (2016) estimated that there are five extant populations with only three that “are likely to be stable and recruiting; the remaining populations are disjunct to short stream reaches.” Historically, Strecker (1931) listed several localities: Llano River in Mason Co., Colorado River in Burnet and Colorado Cos., Bosque River in McLennan Co., Aquilla Creek in McLennan Co., Brazos River in McLennan Co., Leon River in Coryelle Co., Brazos River in Robertson Co. Since 1980, living or recently dead specimens have been found on the Clear Fork of the Brazos River and in the main channel of the Brazos River (Howells et al., 1996; 1997). However, no specific centers of population or beds have been located with the exception of possibly the Brazos River in Washington Co.. A single undocumented specimen reportedly taken in the San Angelo area is the only recent evidence of continued survival anywhere in the Colorado River system (Howells et al., 1996; 1997). Seven live individuals were also found in the Brazos River in Washington Co. (Reimer and Linam 2005). The second largest population in Texas was recently found on the San Saba River (Agrilife Today 2011).

USFWS (2015, 2016) considered the primary threat to this species to be habitat loss and degradation from impoundments, contributing to scouring of riverbeds, sedimentation, modified stream flows, and decreased water quality. Concern was also expressed about dewatering and the restriction of “fish host migration and distribution of freshwater mussels.” Additional threats include the many sand and gravel mining operations found in the region, pollution of waterways, and the high probability that climate change will exacerbate threats. The species is considered “highly vulnerable to stochastic events” (USFWS 2015). Additionally, there is concern about contaminants, including, but not limited to, ammonia, nitrogen, phosphorus, copper, mercury, pharmaceuticals, hormones, and oil spills. Three non-native invasive species, golden algae, zebra mussel, and the black carp, have been identified as threats or potential threats.