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More Higgins eye reintroductions into the Chippewa River

Higgins eye pearlymussel. Photo by Gary Wege/USFWS.

Higgins eye pearlymussel. Photo by Gary Wege/USFWS.

By Tamara Smith
Minnesota-Wisconsin Ecological Services Office

In August, biologists from the Minnesota-Wisconsin Field Office, Regional Office and the Wisconsin Department of Natural Resources assisted biologists from Genoa National Fish Hatchery in releasing 3,000 Higgins eye pearlymussels in the Chippewa River in Wisconsin -- marking the second year of this exciting effort!

The Higgins eye pearlymussel was listed as endangered in 1976. Since then, the known range has expanded, along with increased monitoring efforts, improvements in sampling and propagation techniques, reintroductions and greater emphasis on research throughout the range. For the past 15 years, the partners have been developing techniques to propagate Higgins eye. Studies focused first on identifying a suitable reproductive host fish, among them largemouth bass, smallmouth bass, walleye and yellow perch. Biologists then began developing, testing and refining techniques to facilitate efficient collection of brooding females, to maximize the likelihood of successful juvenile transformation, and to maintain juveniles in cages as they grew large enough for eventual release. To date, this program has produced more than 5 million juvenile mussels, with releases of subadults throughout six streams in four states. The capability to propagate and reintroduce Higgins eye into habitats that it occupied historically has helped this species along its path toward recovery.

Since the early 2000s, the Chippewa River in Wisconsin has been considered a potential reintroduction location for Higgins eye. The Chippewa River contains high quality mussel habitat, contains the fish hosts, and is likely part of Higgins eye’s historical range. Further, there is a diverse mussel assemblage in the river, including another endangered mussel, sheepnose, suggesting that the water quality is suitable for sensitive species. Additionally, the federally endangered winged mapeleleaf mussel was reintroduced to a nearby site on the Chippewa River in 2016.

The following year marked the first successful reintroduction of Higgins eye into the Chippewa River. In addition to this year and last year’s releases, we and our partners intend to release sub-adult Higgins eye from the St. Croix River (deemed ‘Northern Strain’) into several more sites on the Chippewa River to form a series of nearby reintroduction sites, that over time will become an interconnected, reproducing population spanning several miles of the river. To obtain our target density, we estimate that about 3,000 individuals will need to be released at each location.

Young Higgins eye are reared in cages in the St. Croix River until they are large enough to be tagged and released. Before releasing, each mussel was marked with a black glue dot to indicate it was raised at Genoa. Some also received a unique shellfish tag to help track survival and growth. To eliminate the spread of invasive zebra mussels, these animals are held in quarantine at Genoa for at least 30 days before release. We and our partners plan to monitor these reintroduction sites over time to assess survival, growth and to look for signs of reproduction.

Last updated: June 8, 2020