Unique mussel found in St. Croix River proposed for endangered species designation

Salamander mussels have been widely wiped out, but the St. Croix remains a stronghold.




4 minute read

Salamander mussels, St. Croix River (Noah Berg/iNaturalist)

Another mussel species found in the St. Croix River has been nominated for protection under the federal Endangered Species Act. If approved, the salamander mussel (Simpsonaias ambigua) would become the sixth St. Croix mussel species designated as endangered.

As part of the proposed listing, fifty-two miles of the St. Croix River from the St. Croix Falls dam to the mouth at Prescott would be designated as “critical habitat” for salamander mussels. It would be part of 2,012 miles of river across 14 states proposed for the designation.

“We worked with species experts to conduct a species status assessment for the salamander mussel,” the agency said. “Our species status report includes the best scientific and commercial data available concerning the status of the salamander mussel, including the impacts of past, present and future factors affecting the species. Based on the report and other information, we determined that the species faces extinction and meets the definition of endangered under the Endangered Species Act.”

The organism is already listed as threatened by both the states of Minnesota and Wisconsin. Federal designation provides a higher level of protection and a coordinated recovery effort.

The St. Croix is the only river in Minnesota where the salamander mussels are found today. In Wisconsin, they’re found in the Chippewa, Wisconsin, and Black Rivers. But the St. Croix has the most widespread population, according to Lisie Kitchel, a biologist with the Wisconsin Department of Natural Resources who has conducted mussel surveys throughout the state.

“[The] St. Croix has good habitat for them throughout, whereas the other rivers have more localized habitat,” Kitchel said.

The Fish and Wildlife Service says salamander mussel live in fairly swift rivers and streams with slabs of rock or bedrock crevices that are dark, with a solid surface to provide stability and protection from the current. Hiding out in the river’s nooks and crannies means most people never see a salamander mussel throughout its typical ten-year lifespan.

Reciprocal relationship

The salamander mussel is unique as the only member of its family is that it doesn’t use fish as its means of reproduction. The mussel instead relies on mudpuppy salamanders to host the mussel’s young for three to four weeks before the larvae are big enough to survive on the river bottom. Like all mussels, reproduction requires a host where the larvae can cling to gills while they grow into their adult forms.

It’s believed that the mussels may infest the salamanders with their young when the amphibians eat the adult mussels, representing a mutually beneficial relationship between the species, and an ultimate sacrifice by the mussel to perpetuate its genetics.

Thus, the future of the salamander mussel is tied to the fate of mudpuppies, which are declining in many places due to pollution and other factors. The St. Croix River seems to be a stronghold for both the mussel and the amphibian.

“The St. Croix has lots of rock outcrops with piles of boulders at the base and ledgey rock wall habitat the extends into the water,” Kitchel said.

Both the salamander mussel and its mudpuppy host prefer such places. Their shared habitat preference brings the two creatures in contact with each other, maintaining a fragile relationship over thousands of years.

Mudpuppy salamanders are placed in a container during laboratory efforts to infest them with salamander mussel glochidia. (Megan Bradley/USFWS)

Today, the mussel has been lost from at least 50 percent of its historic range, and the decline continues.

The U.S. Fish and Wildlife Service has found that the species is now at high risk of extinction. It points to threats such as water contaminants, changes in flow, landscape alteration, invasive species, and risks to mudpuppies. Its experts found that the greatest threat to the species is habitat destruction. Increased silt and sediment flowing into rivers because of dams, land use, climate change, or other reasons can easily bury the rocky habitat the mussels and their mudpuppy hosts require.

Another worrying risk is invasive zebra mussels. The non-native mussels are found in the St. Croix beginning near the Boom Site downstream to the Mississippi. They can cover native mussels, ultimately suffocating them.

Extinction warning

The Center for Biological Diversity, a nonprofit conservation organization based in Arizona, petitioned the Fish and Wildlife Service to list the Salamander Mussel and four other species as endangered in 2010. The recent announcement is a result of that request.

“Freshwater animals are at the forefront of the extinction crisis in the United States and the Endangered Species Act is the most powerful tool we have to make sure they aren’t lost forever,” said Tierra Curry, a senior scientist for the group. “Protecting these five little-known species will make sure they have a future and will also help keep rivers cleaner for wildlife and for people.”

Forty-one species of mussels live in the St. Croix River and its tributaries, making it one of the most prized mussel systems in the world. Scientists believe that, while mussels were wiped out from rivers across the country during the 19th and 20th centuries, the St. Croix did not lose any of its native mussel species.

Today, five mussel species found in the river are already designated as endangered: Higgins Eye (Lampsilis higginsii), Sheepnose (Plethobasus cyphyus), Snuffbox (Epioblasma triquetra), Spectaclecase (Cumberlandia monodonta), and the Winged Mapleleaf (Quadrula fragosa). The Salamander Mussel would be the sixth.

Designation of salamander mussels under the Endangered Species Act would make it a high priority for restoration by the U.S. Fish and Wildlife Service and partners. The Genoa Hatchery in Wisconsin is already working to propagate salamander mussels, hoping it can help provide more specimens to return to its native range.

Endangered Species Act protection and the designation of the lower river as critical habitat for the Salamander Mussel will not increase regulations of private activities. Instead, the determinations put requirements in place for projects conducted by the federal government, or with federal funding.

The proposal to list the salamander mussels under the Endangered Species Act is now open to public comment until October 23.

Comments can be submitted online or by mail at Public Comments Processing, Attn: FWS-R3-ES-2023-0058, U.S. Fish and Wildlife Service, MS: PRB/3W, 5275 Leesburg Pike, Falls Church, VA 22041–3803. Commenters are encouraged to research the proposal before commenting: “Please note that submissions merely stating support for, or opposition to, the action under consideration without providing supporting information, although noted, do not provide substantial information necessary to support a determination.”


4 responses to “Unique mussel found in St. Croix River proposed for endangered species designation”

  1. Alex Franzen Avatar
    Alex Franzen

    Really cool read! However, mudpuppies like other salamanders are amphibians rather than reptiles.

    1. Greg Seitz Avatar
      Greg Seitz

      Thank you! Don’t know how I screwed that up. Fixed now.

  2. Cyndi Avatar

    Wouldn’t you have to protect the Mud Puppies also in order to protect the mussels?

  3. Gary Sololmonson Avatar
    Gary Sololmonson

    Great article and thank you mudpuppies!!!


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Unique mussel found in St. Croix River proposed for endangered species designation