Rare Mussels Stage a Comeback in the St. Croix

Government scientists are helping an endangered mussel return to its native waters.

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The author works for the U.S. Fish and Wildlife Service Midwest Region. The article was originally published on the agency’s website.

U.S. Fish and Wildlife Service Midwest Regional Director, Tom Melius, holds up an endangered winged mapleleaf mussel. The mussel was found during a routine check of underwater lines in the St. Croix River.
U.S. Fish and Wildlife Service Midwest Regional Director, Tom Melius, holds up an endangered winged mapleleaf mussel. The mussel was found during a routine check of underwater lines in the St. Croix River. (USFWS photo)
This winged mapleleaf mussel lives in the St.Croix River between Minnesota and Wisconsin. The turquoise tag indicates that it is part of the U.S. Fish and Wildlife Service's project to restore the endangered species.
This winged mapleleaf mussel lives in the St.Croix River between Minnesota and Wisconsin. The turquoise tag indicates that it is part of the U.S. Fish and Wildlife Service’s project to restore the endangered species. (USFWS photo)

Nestled in the gravel beneath the waves of many rivers there live small endangered species that at first glance appear to be no more than oddly shaped rocks. Silent and unassuming, many freshwater mussels are fighting their way back from the brink of extinction with help from the U.S. Fish and Wildlife Service.

Service staff from the Genoa National Fish Hatchery in Genoa, Wisconsin and the Twin Cities Ecological Services Field Office in Bloomington, Minnesota, are working with state and federal partners to restore the winged mapleleaf mussel to the Mississippi River and its tributaries. The winged mapleleaf was once prominent in the many waterways that lead into the Mississippi River. Today, the mussel’s existence is threatened by pollution and invasive species.

Complicating the recovery of the species is its unique approach to reproduction. Like most freshwater mussels, the successful reproduction of the winged mapleleaf depends on a host fish. Fertilized winged mapleleaf larva must successfully attach to the gills of a host fish, normally a channel catfish, to grow. Eventually the larva will fall off the host fish into the river bottom, where it will continue its journey to adulthood if the habitat is suitable where it falls.

Unlike a bear or eagle, a winged mapleleaf can fit in the palm of your hand. So how do Service staff find these small creatures year after year? Luckily, mussels tend to stay in one place. Divers place mussels along a fixed underwater line at a recorded location. Before mussels are placed along the line, they are marked with an identifying tag. By placing mussels together on a collection of lines located in the St. Croix River, divers can quickly locate winged mapleleaf mussels during their short breeding period.

Throughout late summer and early fall, Service employees check the lines to see if the mussels are reproducing, referred to as brooding. Winged mapleleaf mussels that are brooding are collected and transported to Genoa National Fish Hatchery where their larva are exposed to host channel catfish. The host catfish are kept at the hatchery until the spring, when they are then placed into cages in the wild for the young mussels to detach from their gills.

Reintroduction of the winged mapleleaf to the Mississippi and other rivers will take time, but with the help of the U.S. Fish and Wildlife Service and partners, the little mussel now has a fighting chance.


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One response to “Rare Mussels Stage a Comeback in the St. Croix”

  1. Willy53 Avatar
    Willy53

    Understanding the reproductive cycles of these various endangered mussel species gives a clear picture of how difficult it is to facilitate their comeback. It is hard for me to understand how the new St. Croix Bridge crossing was approved despite the existance of the Endangered Species Act. Not only has the bridge displaced thousands of native endangered mussels but it is highly likely that the presence of construction equipment and machinery will facilitate an invasion of the invasive zebra mussel which will destroy the ecological zone in which the native mussels exist. To expect the entire construction process associated with the bridge pier installation to be completed without one zebra mussel escaping cleaning and detection on heavy construction equipment is a pipe dream. This will be a double whammy to the preservation of river habitat since the pier sites were home to the largest collection of native mussels in the country. Indeed, much was lost with the legislation that provided the exemption necessary to ignore the Wild and Scenic Rivers Act. Not only here on the St. Croix but all over the country each and every designated Wild and Scenic River is now subject to the template provided by Senator Klobuchar and Representative Bachmann that is a roadmap for encroachment on one of the formerly most effective environmental laws ever written. The US Fish and Wildlife Service performs critical work to save endangered species but the future of river mussels all over the US has just been cloudied by this unfortunate legislation.

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Rare Mussels Stage a Comeback in the St. Croix