Tampico Pearlymussel

Cyrtonaias tampicoensis tecomatensis

Description

The Tampico pearlymussel is a large, bivalve (two-shelled) mussel with an oblong shell. The shell-length of the Tampico pearlymussel can be as long as 5 in (13 cm). The color of the outside of the shell ranges from a dull yellowish-brown to dark brown and black. The inside of the shell (or nacre) is lustrous, and can be colored purple, lavender, pink, salmon, or white. If the mussel contains a pearl, it is the same color as the nacre. About three to four percent of mature individuals contain a pearl in their soft tissue, and a similar percentage have a less-valuable pearl attached to the shell. Gem-quality pearls can exceed 0.4 in (10 mm) in length, but these are exceedingly rare.

Behavior

The Tampico pearlymussel lives on the bottom of slow-moving rivers and streams, partly buried in fine-sediment. It feeds by filtering fine organic detritus and algae from the water. It breeds by releasing male and female gametes (ova and sperm) into the water, where external fertilization occurs. After a short time, the larvae settle to a suitable bottom habitat, where they spend the rest of their lives.

Habitat

The Tampico pearlymussel occurs in slow-moving rivers and streams, in relatively stable, soft-bottom habitat. Although its natural habitat does not include lakes, the species does well in artificial impoundments in Texas. In fact, these reservoirs now support some of the largest populations of the Tampico pearlymussel. They typically occur in water less than about 20 ft (7 m) deep, but may occur in deeper places in reservoirs.

Distribution

The Tampico pearlymussel ranges from northeastern Mexico to the Colorado and Brazos Rivers of Central Texas, with an important center of abundance in the watershed of the Rio Grande (a binational river). The Concho River in western Texas, or the "river of shells," was named by early Spanish colonists in reference to a great historical abundance of the local population of this species. The endangered subspecies Cyrtonaias tampicoensis tecomatensis occurs in northeastern Mexico. Some populations in Texas are still relatively healthy, and the native Tampico Pearlymussel is not listed as an endangered species in the United States.

Threats

The habitat of the Tampico pearlymussel has been degraded by siltation and other disturbances, by pollution with nutrients, sewage, industrial chemicals, and pesticides, and by other factors associated with human activities in the watersheds of their streams and rivers (such as dewatering due to excessive water withdrawals for irrigation during times of drought). It has also been excessively harvested as a source of freshwater pearls.

Conservation and Recovery

The habitat in northeastern Mexico of the endangered subspecies, Cyrtonaias tampicoensis tecomatensis, is not protected. Although collecting of the endangered subspecies is illegal, as is any international trade (it is listed by the Convention on International Trade in Endangered Species—CITES), the rare Tampico pearlymussel is still being poached in its Mexican range, and its habitat is still subject to degradation. Active recovery efforts have not been undertaken.

Contact

Instituto Nacional de Ecología
Av. Revolución, 1425
Col. Campestre, C.P. 01040, Mexico, D.F.
http://www.ine.gob.mx/

Reference

Howells, Robert G. 1996. "The Tampico Pearly-mussel (Cyrtonaias tampicoensis ) Shades of the Old West." Academy of Natural Sciences. http://coa.acnatsci.org/conchnet/how696.html. [Date Accessed: 3 August 2000].