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Listing Proposed for Last Freshwater Mussel in NM

WASHINGTON (CN) - The last of eight native species of freshwater mussel in New Mexico has been proposed for listing as an endangered species under the Endangered Species Act. The other seven mussel species are now extinct in the state, according to the New Mexico Department of Game and Fish.

The four and a half inch long Texas hornshell mussel, historically found in New Mexico, Texas and Mexico, has lost 85 percent of its range in the United States due to water diversion, water contamination from the oil and gas industry, increased salinity from agriculture runoff, sedimentation from grazing, loss of native species and the introduction of exotic species.

Native fish species are crucial to the life-cycle of freshwater mussels. "Fertilized hornshell eggs develop into larvae and are released from the adults into the water where they are consumed by fish. The larvae then form parasitic cysts in the host fish's gills, face or fins where they transform into the juvenile form and are released. If they are released in a suitable area, they can attach to a substrate and complete their development, becoming reproductive adult mussels," the agency said. Those mussels that survive to adulthood can live up to 20 years.

The hornshell is still found in small populations in the Rio Grande, Pecos River and Devil's River in Texas. The species' status in Mexico is unclear, the Service said in their announcement.

"We have low confidence in the species' current condition throughout most of the Mexican range. One or more of these populations may still be extant, or they may all be extirpated. We have no recent data on the species' occurrence in Mexico; the last live recordings are from the mid-1980s. Because of this uncertainty, we did not rely on the Texas hornshell's distribution in Mexico when evaluating the viability of the species," the agency said in the listing proposal.

"The Texas hornshell and other mussels across the Southwest are struggling because the waterways they call home are being altered and impacted by declining water quality and quantity," Dr. Benjamin N. Tuggle, the Service's Southwest Regional Director, said. "Declining freshwater mussel populations are signs of an unhealthy aquatic system, which has negative implications for the fish, wildlife and communities that depend upon those rivers and streams."

The hornshell was first recognized as a candidate species for federal listing in 1989, but it has languished in listing limbo for 27 years due to higher listing priorities.

In 2011, the Center for Biological Diversity (CBD) conservation group and its allies secured a settlement with the U.S. Fish and Wildlife Service to speed listing decisions for hundreds of species under a court-mandated multi-year work plan.

"This is the final year of the 757 species settlement agreement between the Center and the Fish and Wildlife Service. To date 147 species have been granted endangered species protection under the agreement, and another 35, including the hornshell, have been proposed for protection," the CBD said in response to the Service's listing proposal, published Wednesday.

Under the ESA, the listing process is mandated to take no more than two years. A study published in the international scientific journal Biological Conservation found that the average listing period is 12 years, and that vertebrate species were listed faster than plants or invertebrates, such as the mussels. The study further noted that, in addition to the effects of policy choices, lawsuits and taxonomy on listing, presidential administrations also have a significant effect on the listing process.

"Presidential administration, in particular, had a major impact on listing of species, with only 62 species listed under the second Bush administration compared to 268 under the Obama administration and 522 under the Clinton administration," the CBD said. Meanwhile, 42 species became extinct while waiting for protection between 1973 and 1995, according to the study.

Comments and information regarding the listing proposal are due Oct.11.

Photo caption: Adult Texas hornshell from the Black River, New Mexico. Photo by Joel Lusk, U.S. Fish and Wildlife Service.

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