Texas Fawnsfoot (Truncilla macrodon)
There are more than 50 mussel species in Texas, and they play an important role in our waterways. The presence of diverse and reproducing populations of mussels indicates a healthy aquatic system, which means good fishing and good water quality. When the populations are at risk, there will be problems for other fish and wildlife species, and people, too.
One of those species, the Texas Fawnsfoot, or Truncilla macrodon, is in trouble.
The Texas fawnsfoot is a state-listed threatened species. However, it’s currently under review for federal protection under the Endangered Species Act. The Brazos River Authority’s Environmental Services Department regularly monitors different fish and wildlife species, including freshwater mussels, as a way of tracking the health of the Brazos River basin ecosystem.
Freshwater mussels are an indicator of a healthy aquatic system. They are filter feeders and thus contribute to water clarity and quality by removing plankton and pollutants from the water.
The sudden disappearance of mussels in an area not recently subject to prolonged drought often indicates water pollution problems.
Historically, freshwater mussels were collected commercially for food, pearls and button making. Commercial harvesting is now regulated by the Texas Parks and Wildlife Department and requires a license and annual reporting to the department.
The Texas fawnsfoot is most commonly observed in riffles within streams and rivers but has been identified in a variety of habitats.
Within the Brazos River basin, the Texas fawnsfoot has been found in multiple locations, including the Clear Fork of the Brazos River, the Brazos River between Possum Kingdom Lake and Lake Granbury, the Brazos River below Waco, the Navasota River and the Little River.
However, after the 2011 drought, the status of the population in the Clear Fork of the Brazos River is in question (Bonner et al. 2018).
Little is known regarding the life history requirements of the Texas fawnsfoot. They are presumed to have a similar reproductive cycle to other Truncilla species, which are long-term brooders that parasitize solely on Freshwater Drum Aplodinotus grunniens to complete their life cycle (Howells 2014; Barnhart et al. 2008).
Like all freshwater mussels, the Texas fawnsfoot is relatively inactive and capable of moving only small distances. Their primary mode of moving or colonizing new areas is accomplished by the movement of the fish hosts or by high flow events that scour adult mussels from their current location and move them downstream.
The breeding season of the Texas fawnsfoot has not been definitively documented. Still, it is presumed to follow the primary breeding season of other freshwater mussels, which most frequently occurs from February to June.
A significant amount of research is done on freshwater mussels. Agencies across the state are researching them, including the U.S. Fish and Wildlife Service, the Texas Comptroller of Public Accounts, the TPWD, and the Brazos River Authority.
Several universities also are researching freshwater mussels, including Texas A&M University, Texas State University, Baylor University, the University of Texas at Tyler, and Auburn University. These studies include surveys to identify new populations, genetic investigations, and tolerance studies.
The TPWD also maintains the Texas Mussel Watch Program, where members of the public can submit their observations of mussels to help gain a better understanding of the distribution and status of mussels.
In addition to regulating commercial harvesting of mussels, the TPWD also regulates the taking of mussels by individuals by requiring a fishing license and freshwater fishing endorsement.
In August 2020, the Brazos River Authority submitted a Candidate Conservation Agreement with Assurances to the U.S. Fish and Wildlife Service for consideration, in which the BRA commits to performing voluntary conservation activities aimed at reducing threats to the Texas fawnsfoot in the Brazos basin. It is anticipated that this agreement will be executed sometime in 2021.
For more information, go to:
- Barnhart, M.C., W.R. Haag, and R.N. Williams. 2008. Adaptations to host infection and larval parasitism Unionoida. Journal of the North American Benthological Society. 27:370-394.
- Bonner, T.H., E.L. Oborny, B.M. Littrell, J.A. Stoeckel, B.S. Helms, K.G. Ostrand, P.L. Duncan, and J. Conway. 2018. Multiple freshwater mussel species of the Brazos River, Colorado River, and Guadalupe River basins. Final Report to Texas Comptroller of Public Accounts.
- Howells, R.G., 2014. Field Guide to Texas Freshwater Mussels. BioStudies, Kerrville, TX.