programs Natural Resources

Freshwater Mussels - Central Texas

smooth pimpleback, Texas pimpleback, Texas fatmucket, Texas fawnsfoot, false spike


Researchers wade into the Upper Guadalupe River to search for mussels.

Until recently, the mussels of central Texas were mostly a mystery. Their distribution, life cycle and habitat needs and threats to the species were not known.

On Dec. 15, 2009, the U.S. Fish and Wildlife Service (FWS) issued a 90-day finding that listing the mussels as endangered may be warranted based on evidence of threats from loss and modification of habitat, reduction in abundance and the impact of rare-shell collectors.

The next phase, a 12-month review, was completed in 2011 and concluded that listing the smooth pimpleback, Texas pimpleback, Texas fatmucket and Texas fawnsfoot species was warranted but precluded by other higher priority actions. Since then FWS has conducted a series of reviews of the species.

FWS is now completing a more thorough assessment, which should produce a report and proposed listing recommendation by the end of 2019.

Research Description

In 2016, the Texas Comptroller of Public Accounts (CPA) contracted with Texas State University (TxState) to quantify ecological and biological information to determine the distribution, abundance, population structure, habitat associations and occurrence of the species in the Colorado, Brazos and Guadalupe river basins.

In these Central Texas areas, researchers searched for the mussels using snorkels and scuba equipment to assess presence/absence, abundance, density, distribution, population structure and mussel habitat associations. Researchers also evaluated the mussels’ tolerance levels and responses to environmental factors such as temperature, oxygen levels, suspended sediment and salinity. In addition, the researchers conducted analyses to see what level of flows benefited and harmed the species and established sites where they could mark individual mussels to track their growth and movement over time via multiple surveys.

The researchers have completed these studies and submitted final reports and data to CPA and FWS.

Ongoing work is focused on figuring out how to raise mussels in hatcheries. The final stage of the research will compare long-term growth, health and survival of mussels in both artificial and natural water systems.

All of the deliverables are due at end of contract on Feb. 28, 2020, and will be made available to the public.

Why This Research Matters

Freshwater mussels play an important role in aquatic ecosystems. At different life stages, they are food for fish, mammals, birds and turtles. As filter feeders, they help clean the water they live in by collecting organic particles, bacteria and algae, as well as accumulating contaminants in their soft tissues. Because they have limited mobility and are typically long lived, freshwater mussels are sensitive to changes in their environment and can serve as bio-indicators of water quality and overall ecological health.

Research during the past several years indicates that these Central Texas mussels are in decline; however, there were significant knowledge gaps including a limited understanding of the species’ range and biology. A federal listing of some or all of these species could affect water users, landowners and businesses that rely on freshwater sources or conduct activities in or adjacent to mussel habitat.

The work by TxState expanded the available data and analysis about the species to ensure listing decisions are based on accurate and up to date science. The regular updates on this work and CPA-hosted meetings gave stakeholders a way to learn about the species and engage with the FWS about possible conservation actions. Now many of those stakeholders are working on formal conservation plans to help protect the long-term survival of the species and ensure regulatory certainty for their operations in and along the rivers of central Texas.

2017 Mussel Survey Data

The size of the dots on the map represent the number of mussels found at each survey site, not the size of the survey site. All surveys were conducted on public waters via public access sites or with the permission of the landowner.

View map of mussel locations across Texas