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A species of freshwater mussel found in pockets of the Allegheny River might soon be protected under the Endangered Species Act, as proposed by the U.S. Fish and Wildlife Service.

Salamander mussels are relatively small: their dark brown, oval shells grow to just two inches. Some biologists liken the ecological role of salamander mussels — and other freshwater mollusks — to a river’s liver as they filter bacteria, algae, detritus and even heavy metals from the water. Though perhaps the invertebrates could be considered a river’s spine — mussels provide structure to a river’s bottom as their colonies burrow into sand and gravel beds, which prevents silt, clay and sand from shifting.

Map of Pennsylvania rivers

Colonies of salamander mussels, shown in dark green, are found in pockets of the Allegheny River, along with French Creek and its tributary, Cussewago Creek. The mussels were found in Dunkard Creek, shown in red along the PA-WV border, before being wiped out in 2009 by a toxic algae bloom caused by mine discharge. Image from the Pa. Fish And Boat Commission: Species Action Plan, June 2023

There are just 66 known salamander mussel populations in the U.S. across 14 states. In Pennsylvania, they’ve been identified at several spots in the Allegheny River, including near Freeport and Cheswick. And they’ve been found farther north in French Creek and its tributary, Cussewago Creek.

The salamander mussel’s limited range is partly due to environmental impacts, said Nevin Welte, a non-game biologist for the Pennsylvania Fish and Boat Commission. “On the Allegheny, for example, that river’s dredged for maintaining barge traffic, commercial sand and gravel dredging, historically.”

Salamander mussel populations have declined by approximately 40% from historic levels, which is why the U.S. Fish and Wildlife Service has proposed listing it as an endangered species, said Jessica Pruden, a wildlife biologist for the federal agency.

U.S. range of salamander mussel.

The salamander mussel is critically imperiled in states shaded red, including Pennsylvania. Image from Pennsylvania Fish And Boat Commission: Species Action Plan, June 2023

The mudpuppy connection

The salamander mussel’s unique life cycle further contributes to its danger of extinction. All freshwater mussels rely on a host to reproduce: During the larval stage, a mussel attaches itself to the gills of a fish. Once big enough, it leaves the fish and drifts down to the river bottom. However, salamander mussels attach themselves to the gills of mudpuppy salamanders — they’re the only freshwater mussel in North America to use an amphibian host.

“Of course, mudpuppies are also vulnerable to man of the same threats that salamander mussels are vulnerable to,” said Pruden, who notes that while some species of mussels can hitch a ride to multiple types of fish, the salamander mussel only uses the mudpuppy as a host.

A person holding a mudpuppy

A mudpuppy found in the Allegheny River. Julie Grant / The Allegheny Front

Much remains a mystery about freshwater mussels, said Arthur Bogan, the Research Curator of Mollusks for the North Carolina State Museum of Natural Sciences. For example, it’s possible that various mussel species specialize in filtering different pollutants from rivers and lakes — researchers are just starting to study those questions.

Surveying Salamanders in Hopes of Finding an Endangered Mussel

In the meantime, freshwater mussels and their habitats continue to be threatened: Of the more than 300 species in North America, Bogan estimates that at least 30 have gone extinct.

“It would have been really neat to be able to snorkel in the Allegheny in 1500 to see what was there, what the river looked like at that time,” he said.

The public comment period on whether the salamander mussel should be categorized as endangered closes on Oct. 23.