Higgins Eye Pearlymussel
Higgins Eye Pearlymussel
|Listed||June 14, 1976|
|Family||Unionidae (Freshwater mussel)|
|Description||Tan or brown shell with fine black rays.|
|Habitat||Major rivers and tributaries.|
|Reproduction||Fertilized larvae are released in the spring.|
|Threats||Dam construction, dredging, siltation, pollution.|
|Range||Illinois, Iowa, Minnesota, Missouri, Wisconsin|
The Higgins eye pearlymussel (Lampsilis higginsii ) averages 2.4 in (6.1 cm) in length, with females slightly smaller than males. Fine black rays are present along the growth lines against a background shell of tan to brown.
The Higgins eye is a long-term breeder, holding fertilized glochidia (larvae) over winter and releasing them in spring. The larval host fish is thought to be the sauger or freshwater drum. Females reach sexual maturity by their third year.
This species inhabits major rivers and tributaries in depths of up to 15 ft (4.6 m). It has been found on mud-gravel bottoms in areas of swift current.
The Higgins eye is endemic to the Mississippi River and its major tributaries. It was found in the mainstream of the Mississippi River from north of St. Louis, Missouri, to the Twin Cities, Minnesota. Population centers have been documented near Prescott, Minnesota; La Crosse and Prairie du Chien, Wisconsin; and Muscatine and Davenport, Iowa.
Populations were found in the Illinois River from Mason County to the confluence of the Mississippi; in the Sangamon River near Chandlerville, Illinois; in the St. Croix River near Hudson, Wisconsin; in the Wapsipinicon River near Dixon, Iowa; in the Cedar River near Cedar Bluff, Iowa; and in the Iowa River near Gladwin, Iowa.
Although widely distributed, this mussel occurred in discrete localities and was never considered numerous. In the late 1970s and early 1980s the Mississippi River was heavily surveyed for occur-rences of the Higgins eye. Scattered populations were found to survive in sections of river near La Crosse, Wisconsin; from the Minnesota state line south to Prairie du Chien, Wisconsin; from Clayton downstream to Dubuque, Iowa; and from Clinton south to West Burlington, Iowa. Except for a remnant population near the confluence of the Missouri River, population centers south of West Burlington in the mainstream appear to have been largely extirpated. The St. Croix River still supports several populations upstream from Hudson (St. Croix County), Wisconsin.
Biologists estimate that the Higgins eye has been eliminated from nearly 55% of its historic range.
Construction of major dams for flood control and electricity generation have created conditions along portions of the upper Mississippi River that are no longer conducive to the survival of the Higgins eye. River impoundments have inundated habitat upstream and contributed to erratic water flows, altered water temperatures, and increased siltation downstream. Degradation of water quality caused by municipal, industrial, and agricultural effluents has also contributed to this mussel's decline.
A major research study on the mussel, completed in 1989, found that habitat characteristics of adult Higgins eye mussels do not vary noticeably from those of many common species of mussels in the upper Mississippi River. Adult Higgins eye mussels were found in a wide range of main channel border habitats with various current velocities and sediment types. However, the mussel was most common at sites where summer currents ranged from 0.5-0.7 ft per second (15-21.3 cm per second) and where there were medium-fine to fine sand substrates. These are common habitats in the main channel border area throughout much of the upper Mississippi River. Therefore, it appears unlikely that a lack of suitable hosts or habitat is responsible for the observed sparse distribution of this species. How host fish distribution relates to the distribution of the Higgins eye is still unknown, but it may be that there is an insufficient overlap of the range of the mussel and its needed hosts. This hypothesis remains untested and is difficult to study directly in the large Mississippi River system, but it may be supported by the abundance of the pocketbook mussel, which has similar hosts but prefers coarser substrates. It is also possible that habitat requirements for juveniles may be limiting factors for many species.
Conservation and Recovery
Seven sites have been designated as habitat essential to the survival of the Higgins eye pearly-mussel. These are 1) the St. Croix River above Hudson, Wisconsin; 2-4) the Mississippi River at Whiskey Rock, Prairie du Chien, and McMillan Island, Wisconsin; 5) Harpers Slough, Iowa; and 6-7) Cordova and Arsenal Island, Illinois.
Relocation of mussels to existing mussel beds not currently populated with Higgins eye is recommended in the U. S. Fish and Wildlife Service Recovery Plan for this species. Research is ongoing to determine practical methods of propagation and reintroduction.
Havlik, M. E. "The Historic and Present Distribution of the Endangered Mollusk Lampsilis higginsii (Lea, 1857)." Bulletin of the American Malaco-logical Union (1980): 19-22.
"Recovery Plan for the Higgins Eye Pearly Mussel."1982. U. S. Fish and Wildlife Service, Twin Cities, Minnesota.
"Relocation of Freshwater Mussels in Sylvan Slough of the Mississippi River near Moline, Illinois." 1981. Shappert Engineers/Ecological Analysts, Belvidere and Northbrook, Illinois.
"Survey of Freshwater Mussels at Selected Sites in Pools 11 through 24 of the Mississippi River." 1981. Ecological Analysts, Northbrook, Illinois.