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Nov. 5, 2009
15 Texas Freshwater Mussels Placed on State Threatened List
AUSTIN, Texas — Despite the colloquial poetry of their names, Texas mussels like the golden orb, Louisiana pigtoe, sandbank pocketbook and Texas fatmucket are not well known to most people. Yet, their placement on the state threatened species list may benefit many people by putting a bit more muscle behind efforts to protect rivers, water quality and freshwater habitats that sustain many other fish and wildlife species.
The Texas Parks and Wildlife Commission on Nov. 5 acted to place 15 of the 50 known Texas species of freshwater mussels on the state threatened list. Currently, state fisheries regulations allow harvest of most of these mussels, though practically none of them ever get large enough for harvest. The listing makes it a Class C misdemeanor to kill or collect them.
The state listing comes as the U.S. Fish and Wildlife Service is pondering whether to list some of the 15 as threatened or endangered under the U.S. Endangered Species Act, which would carry more weight and higher penalties. Federal biologists already consider one of the 15, the Texas hornshell, a candidate for listing, and this winter they are expected to issue findings for 12 other species among the 15. The sandbank pocketbook and Texas pigtoe are the only two of the 15 not currently under federal listing review.
Freshwater mussels (unionids) are an important component of healthy aquatic ecosystems, both as a food source for many other aquatic and terrestrial creatures, and as key indicators of water quality and habitat health. In early life stages, mussels are food for a variety of aquatic insects, small fishes, and water birds; as they mature they become significant food sources for larger fishes, waterfowl, and terrestrial animals. Ultimately, their protection helps preserve and enhance the hunting, fishing, and outdoor recreation opportunities that are part the Texas heritage.
Like frogs and other amphibians that are sensitive to water quality problems, freshwater mussel populations have declined throughout North America. They are sensitive to disturbance because they are relatively immobile, sometimes staying in a single spot their entire lives. Mussels are also very long-lived, some living over 100 years, and are very slow-growing. They have a complex life cycle that is easily disrupted, causing reproductive failure. Habitat alteration and loss, illegal and over harvesting, and competition from introduced or invasive species are some of the factors in their decline.
Nationwide, more species of freshwater mussels are listed as threatened and endangered than any other group of animals. Of the nearly 300 species known to have lived in the U.S., 18 are believed to be extinct, and 60 are currently listed as federally endangered or threatened, including one species that may occur in Texas, the Ouachita rock-pocketbook.
Volunteers can play an important role to help conserve understand freshwater mussels through Texas Mussel Watch, one of several Texas Nature Trackers volunteer programs run by Texas Parks and Wildlife Department. To find out more about Texas Nature Trackers or to sign up for a Texas Mussel Watch monitoring workshop, contact TPWD’s Wildlife Diversity Program at firstname.lastname@example.org or (800) 792-1112, ext. 8062.
All of the 15 mussels listed as state-threatened Nov. 5 live in very limited habitats and are sensitive to water quality degradation, and thus are now known to occur only in a few highly specific geographical areas. Below is a listing of the 15 species.
- False spike (Quadrula mitchelli) — known from only two disjunct populations, one in central Texas and the other in the Rio Grande drainage.
- Golden orb (Quadrula aurea) — endemic to the Guadalupe-San Antonio and Nueces-Frio systems. Only seven extant populations of this mussel have been noted from the upper and central Guadalupe River, central San Antonio River, lower San Marcos River, and Lake Corpus Christi.
- Louisiana Pigtoe (Pleurobema ridellii) — ranged from eastern Texas drainages into Louisiana, but has been exceptionally rare in recent decades. Since the mid-1990s, small numbers of living specimens have been found in the Neches River and some of its tributaries and the Angelina River.
- Mexican fawnsfoot (Truncilla cognata) — endemic to the central Rio Grande drainage. Extensive historical and current environmental modifications along the Rio Grande of Texas and Mexico suggest any surviving populations are likely at risk.
- Salina mucket (Potamilus metnecktayi) — endemic to the central Rio Grande drainage, has potentially been extirpated from its range in New Mexico and Mexico and undergone dramatic declines in Texas.
- Sandbank pocketbook (Lampsilis satura) — known from southern portions of the Mississippi interior basin and western Gulf drainages of Arkansas, Mississippi, Louisiana, and Texas, considered rare in all states from which it has been recorded.
- Smooth pimpleback (Quadrula houstonensis) — endemic mussel restricted to the Colorado and Brazos River drainages. Surveys conducted from 1980 to 2006 have noted steep declines in the number of extant populations in both river systems.
- Southern hickorynut (Obovaria jacksoniana) — considered rare and a species of conservation concern in seven states. If the species still occurs in Texas at all, it may only persist on Village Creek.
- Texas fatmucket (Lampsilis bracteata) — historically occurred in the Colorado and Guadalupe basins of Central Texas. In the past 30 years, natural and human-induced stressors have lead to the dramatic decline of this species in both rivers. Remaining populations are at risk from scouring floods, dewatering, and poor land management.
- Texas fawnsfoot (Truncilla macrodon) — historically occurred in the Colorado and Brazos drainages of Central Texas. A recently discovered population in the Brazos River between Possum Kingdom and the mouth of the Navasota River represents the only known surviving population.
- Texas heelsplitter (Potamilus amphichaenus) — restricted to the Sabine, Neches, and Trinity rivers of Texas.
- Texas hornshell (Popenaias popeii) — a regional endemic known only from discrete sections of the Rio Grand River in Texas and a short segment of the Black River in New Mexico.. The discovery of 30 individuals in a Webb County portion of the Rio Grande River in 2003 provides the only evidence of an extant population in Texas. Currently listed as a candidate for protection under the U.S. Endangered Species Act.
- Texas pigtoe (Fusconaia askewi — a regional endemic limited to a relatively small area in Texas and Louisiana, including the Trinity River above Lake Livingston, a tributary of the West Branch San Jacinto River, and the Sabine River above Toledo Bend Reservoir.
- Texas pimpleback (Quadrula petrina) — an endemic species confined to the Colorado and Guadalupe drainages. The only confirmed significant population in the Concho River persists, but has been badly reduced by dewatering.
- Triangle pigtoe (Fusconaia lananensis) — endemic to the Neches and San Jacinto Rivers and Village Creek in eastern Texas, but extant populations are limited and the ecological security of most occupied sites is marginal.
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