Lampsilis higginsii (I. Lea, 1857)
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Lampsilis higginsii, Lampsilis higginsi
Basis for Listing
The Higgins eye was the first freshwater mussel to receive federal protection, which took effect in 1972. Degradation of the Mississippi River in the form of navigation improvements and pollution severely restricted the range of this species. Today, the lower St. Croix River has one of the largest remaining Higgins eye populations throughout the species' range. It has been extirpated from the Minnesota River, and is rare in the Mississippi River. The Higgins eye was afforded state endangered status in 1984.
The shell of the Higgens eye is up to 15 cm (6 in.) long, and is inflated, with thick valves and a beak that is pointed forward. The outside of the shell is yellow, greenish, reddish, or brown, often with green rays. This species is sexually dimorphic, with the females having a shell that is rounded and truncate posteriorly, while the males have a shell that is oval. The beak sculpture in both sexes is obscure, and the pseudocardinal and lateral teeth are well developed. The inside of the shell is white, and sometimes pink or salmon in the beak cavity. The Higgens eye resembles the hickorynut (Obovaria olivaria), mucket (Actinonaias ligamentina), and plain pocketbook (Lampsilis cardium) mussels.
The Higgins eye occurs only in the Mississippi River and the lower portion of some of its large tributaries (Havlik 1980). It occupies stable substrates that vary from sand to boulders, but not firmly packed clay, flocculent silt, organic material, bedrock, concrete or unstable sand. Water velocities should be less than 1 m/s (3.3 ft./s) during periods of low discharge. The species is usually found in mussel beds that contain at least 15 other species at densities greater than 0.01 individual/m² (U.S. Fish and Wildlife Service 2004).
Biology / Life History
Mussels are long-lived animals. Members of many species may live for several decades and in some instances a century or more. They spend most of their lives buried in the bottom sediments of permanent water bodies, and often live in multi-species communities called mussel beds (Sietman 2003).
Conservation / Management
The Higgins eye is rare or extirpated throughout most of its former range. The viability of remaining populations in the Mississippi River is jeopardized by the continuing decline in habitat conditions associated with management of the river as a navigation canal; with non-point and point source water and sediment pollution; and by the infestation of non-native zebra mussels (Dreissena polymorpha) in the Mississippi River and its tributaries. Zebra mussels can attach themselves in large numbers to the shells of native mussels, eventually causing death by suffocation.
Conservation Efforts in Minnesota
In the early 1980s, a recovery team consisting of biologists from the U.S. Fish and Wildlife Service, Minnesota and Wisconsin DNRs, the U.S. Geological Survey, U.S. Army corps of Engineers, University of Minnesota, Macalaster College, and Western Wisconsin Technical College drafted the first Higgins Eye recovery plan. The plan identified actions necessary for the recovery of this rare mussel species (U. S. Fish and Wildlife Service 1983). The recovery team subsequently reconvened in the early 2000s to review all Higgins eye research conducted since 1980, and to review the status of the species. A revised recovery plan, taking into account new information and threats, such as the infestation of zebra mussels, was completed in 2004 (U. S. Fish and Wildlife Service 2004).