The Higgins eye, Lampsilis higginsii (I. Lea, 1857), is a federally endangered freshwater mussel found in the upper Mississippi River, lower St. Croix River, Wisconsin River, and Rock River in North America. It occupies sand and gravel riverbeds, where it partially buries itself. The portion of the mussel that is left above the river bed contains the apertures, which are used during filter feeding. Filter feeding involves drawing water into the incurrent aperture, the mussel uses cilia on its gills to filter out food particles, bacteria, and algae, and water leaves through the excurrent aperture. Though most of the Higgins eye's life is spent partially buried in the river bed, they spend their larval stage of development parasitically attached to a fish host. Higgins eye mussels spawn in the summer and release their larvae (glochidia) usually in May, June, July and September. The Higgins eye shell is rounded to slightly elongate in outline, smooth-surfaced, and yellowish brown in color with green rays. Due to the endangered status of Higgins eye a recovery plan was created in 1983 and revised in 2004 by the Higgins Eye Pearlymussel Recovery Team.
endemic to a single nation
Regularity: Regularly occurring
Type of Residency: Year-round
Global Range: (1000-5000 square km (about 400-2000 square miles)) The historic distribution before 1965 was given as the main stem of the Mississippi River from just north of St. Louis, Missouri, to just south of St. Paul, Minnesota; in the Illinois, Sangamon, and Rock Rivers in Illinois; in the Iowa, Cedar, and Wapsipinicon Rivers in Iowa; in the Wisconsin and St. Croix rivers in Wisconsin; and, in the Minnesota River in Minnesota (based on Havlik, 1980; USFWS, 1983). A questionable report of this species in the lower Ohio River was also given (Havlik, 1980). A study by Cawley (1996) extended the reported range of Lampsilis higginsii 98 miles to the south and 82 miles to the north based on the collection of dead specimens. As such, current distribution in the upper Mississippi River is between La Crosse, Wisconsin, and Muscatine, Iowa, as well as the St. Croix, and Wisconsin Rivers (Miller and Payne, 2007).
U.S.A. (IA, IL, MN, MO, NE, WI)
The current range of the Higgins eye has declined to 4 rivers: Mississippi River (North of Lock and Dam 19 at Keokuk, Iowa), lower portions of the St. Croix River between Minnesota and Wisconsin, Wisconsin River in Wisconsin, and lower Rock River between Illinois and Iowa (USFWS 2004).
Baker (1928) described Higgins eye general shell morphology as, "Oval or elliptical, somewhat inflated, solid, with gaping anterior base; beaks placed forward of the center of the dorsal margin, much elevated, swollen, their sculpture consisting of a few feeble ridges slightly looped; anterior end broadly rounded; posterior end truncated in the female, bluntly pointed in the male; ventral and dorsal margins slightly curved, almost parallel; posterior ridge rounded, but well marked; surface shining, marked by irregular growth lines which are better developed at rest periods where they are usually dark colored; epidermis olive or yellowish green with faint green rays. Hinge massive; pseudocardinals erect, triangular or pyramidal, divergent, serrated, two in the left and one in the right valve, with sometimes indications of additional denticles on either side of the single right pseudocardinal; interdentium narrow, flat; laterals short, thick, slightly curved, almost smooth; cavity of the beaks deep, containing the dorsal muscle scars; anterior adductor scar deeply excavated, posterior scar distinct; nacre silvery white, iridescent, often tinged with pink.”
This species has been confused with Lampsilis abrupta from the Ohio River System. Higgin's eye has lower umbo and a lighter periostracum (Havlik, 1981). This species exhibits marked sexual dimorphism with the posterior end in the females sharply truncated with a post-basal swelling. The posterior end in the males is more roundly pointed. A number of species can be confused with L. higginsii. Those cited as most similar are Obovaria olivaria, L. cardium, L. siliquoidea, L. abrupt and Actinonaias ligamentina (Baker, 1928; Cummings and Mayer, 1992). Although nothing has been published specifically on the internal anatomy of L. higginsii, Baker (1928) indicates it is most likely similar to that of other lampsilines.
The Higgins eye is a medium sized freshwater mussel (10-15 cm in length). Its shell is rounded to slightly elongate, thick, with a smooth surface. The shell is usually yellowish brown with green rays. Higgins eye is sexually dimorphic. Female's shells are more rounded and truncate posteriorly, while male's shells are more broadly pointed (MN DNR, USFWS, Baker 1928, Cummings and Mayer 1992, Sietman 2003).
Habitat Type: Freshwater
Comments: This species is found in substrates of mud with a mixture of gravel and stones. It prefers rapidly flowing water (USFWS, 1982). Lampsilis higginsii is characterized as a large river species occupying 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/second during periods of low discharge. They are usually found in mussel beds that contain at least 15 other species at densities greater than 0.01 individual/square meter. In the Mississippi River, the density of all mussels in the bed typically exceeds 10/square meter (USFWS, 1982; Hornbach, 2004). Although historical distribution includes tributaries with a wide range in average mean discharge, current recruiting populations now inhabit rivers with mean annual discharge greater than 500 cubic feet per second suggesting Lampsilis higginsii inhabits large rivers, not small tributaries (Miller and Payne, 2007).
Habitat and Ecology
Higgins eye is a freshwater mussel that lives in large rivers. They are most commonly found in stable sand or gravel but may occur in more coarse substrates with rocks or boulders, or in firmly packed clay, silt, organic material, or occasionally in unstable sand. They occupy areas with moderate current (less than 1 meter per second during moderate discharge. They are commonly found in high quality mussel beds containing at least 15 other mussel species (MN DNR, USFWS, USFWS 2004, Cummings and Mayer 1992, Sietman 2003).
Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.
Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).
Locally Migrant: No. No populations of this species make annual migrations of over 200 km.
Higgins eye is dispersed through its parasitic relationship with fish. The mussel releases its glochidia into the water in order for them to attach to a fish host. The fish host serves as a place to transform and develop into a juvenile mussel, as well as a means for dispersal. Once the glochidial transformation has taken place, they detach from the fish and fall to the riverbed, likely in a different area than their parent mussels. This method of dispersal allows mussels to widely disperse when mussels are otherwise sedentary (Barnhart et al., 2008, MN DNR).
Comments: From USFWS (2004): Among the few published studies on unionid feeding mechanisms are recent studies by Tankersley and Dimock (1992, 1993a, 1993b) who used endoscopic techniques to examine feeding in Pyganodon cataracta. There have been no studies focusing specifically on L. higginsii but generally unionids are filter-feeders, removing small suspended food particles from the water column utilizing the large lamellibranch gills as feeding organs. Feeding rate in bivalves is known to be greatly influenced by temperature, food concentration, food particle size and body size (Jørgensen 1975; Winter 1978).
There have been no studies specifically focused on the feeding habits of Higgins eye, but mussels are generally filter feeders (USFWS 2004). They draw water, and associated suspended particles, in through their incurrent aperture, remove food particles with their gills, and expel the filtered water through their excurrent aperture. The food particles (bacteria, protozoans, algae, and other organic matter) are transported to the mouth by cilia on the gills. Post digestion, waste is released through the excurrent aperture (McMahon 1991).
The sauger has been shown to be a Higgins eye glochidia host (evidence of glochidia metamorphosis and natural fish infestation). Northern pike, black crappie, green sunfish, smallmouth bass, largemouth bass, walleye, sauger, bluegill, and yellow perch have been shown to facilitate glochidial metamorphosis in the laboratory (Waller and Holland-Bartels 1988, Hove 2004). Freshwater drum and sauger are known to be naturally infested with Higgins eye (Surber 1913, Wilson 1916).
Natural predators of adult Higgins eye are likely general mussel predators including river otters, muskrats, striped skunks, mink, raccoons, turtles, and fish (Convey et al., 1989, Pennak 1989, Williams et al., 1993).
Number of Occurrences
Note: For many non-migratory species, occurrences are roughly equivalent to populations.
Estimated Number of Occurrences: 6 - 20
Comments: This species is restricted to a few sites in the following drainages: Copperas-Duck, Flint-Henderson, Lower Rock, Grant-Little Maquoketa, Coon-Yellow, Lower Wapsipinicon, Lower St. Croix, Twin Cities, Rush-Vermillion, La-Crosse-Pine (see USFWS, 1982 and USFWS, 2004). The latest recovery plan lists 10 (up from 7 in previous plan) locations as primary habitats (6 in Mississippi River between river miles 489 and 656, 1 in Wisconsin River, 3 in St. Croix River) and 9 (same as previous plan) as potential secondary habitats, with reintroductions since 2000 into 4 rivers from which it had previously been extirpated (USFWS, 2004), including pool 4 and the Twin Cities region nof the Mississippi River below St. Anthony Falls, Minnesota (Sietman, 2003). Miller and Payne (2007) summarize the distribution following the latest recovery plan (USFWS, 2004) as: upper Mississippi River is between La Crosse, Wisconsin, and Muscatine, Iowa, as well as the St. Croix, and Wisconsin Rivers.
100,000 - 1,000,000 individuals
Comments: Mathiak (1979) reported collecting 45 specimens from the Mississippi River in Wisconsin in 1975 prior to the species' listing as an endangered species in 1976; mostly from a commercial clamming operation. Cawley (1996) noted that 510 specimens of Lampsilis higginsii had been collected since 1980. Hornbach et al. (1995) examined populations in the St. Croix River and estimated populations to be 4,000 mussels at Franconia, 4,000 to 10,000 mussels at Prescott, Minnesota, and 238,000 to 260,000 mussels at Hudson, Wisconsin (all listed as Essential Habitat Areas in the initial recovery plan). Heath (in litt. 1998), and Heath et al. (1999) collected almost 90 L. higginsii from 1987-1999 in the area of the St. Croix river, extending upstream of Franconia, MN to the Interstate Park Area (Taylor's Falls, MN) - about 3 river miles. They estimate L. higginsii population densities of approximately 0.01 individuals/m2. In 2000, mean density estimates of L. higginsii at Interstate Park and Hudson were 0.01 and 0.09, respectively (Heath et al., 2001); these estimates did not reflect a statistically significant change in abundance at either site. Estimates of population size were 9,224 (95% CI = 4,192 - 14,255) at Hudson and 4,212 (95% CI = 358 - 7,886). Hornbach et al. (1995) estimated that there were 4000 live individuals in the St. Croix River at RM 50.2 and as many as 260,000 at RM 17.6. In a recent re-evaluation of the species in the Upper Mississippi River (Miller and Payne, 2007), the number of L. higginsii at Essential Habitat Areas (EHAs) ranged from several thousand to more than 500,000. The species is much less abundant in the Wisconsin River and St. Croix River EHAs. In 2001 this species was found alive at four sites in the Upper Mississippi River National Wildlife and Fish Refuge (formerly Savanna Army Depot) in Illinois/Iowa between RM 544.5 and 558.4 in relative abundance from 0.9 to 2.6% (Sietman et al., 2004).
Higgins eye is a river mussel endemic to the upper Mississippi and lower portions of the St. Croix River, Wisconsin River, and the Rock River. The species used to occur more widely in these rivers as well as the Illinois and Sangamon Rivers in Illinois, Iowa, Cedar, and Wapsipinicon Rivers in Iowa, and Minnesota River in Minnesota (USFWS 2004). It lives partially buried in the riverbed substrate comprised usually of stable sand or gravel. Higgins eye filter feeds, removing organic particles, algae, bacteria, and other particles from the water, in turn cleaning the water of these particles. Mussel larva, glochidia, attach to their fish host's gills or fins, where they complete their development into juvenile mussels. Higgins eye are probably preyed upon by a variety of natural predators (see 'Associations' section for list of predators) (MN DNR, USFWS, USFWS 2004).
Life History and Behavior
Mussels are primarily sedentary, living most of their lives partially buried into the sediment of the riverbed (McMahon 1991). Although they are mostly sedentary, they are able to move small distances with the use of their muscular foot, a hatchet shaped muscle that extends out from between the valves. Relaxation and contraction of the foot allows the mussel to move short distances and to burrow into the sediment (MN DNR).
Freshwater mussels, and presumably Higgins eye, reproduce and brood young regularly. Male mussels release sperm into the water, which are taken up by females, and fertilization occurs in the female’s gills. Embryos develop into larvae (glochidia), which require a fish host in order to metamorphose into juvenile mussels (McMahon 1991). The Higgins eye has evolved a ribbon-like mantle flap that serves as a lure to attract a potential fish host (see 'Associations' section for a description of fish hosts). The mantle flap is described as being minnow-like in appearance, even possessing a dark eye-spot. Mantle flaps in other mussel species may be colored and shaped like a fish food item (Barnhart et al., 2008). A fish will strike at the lure and the glochidia are released into the water. Glochidia attach themselves to the gills or fins of their fish host by pinching onto the tissue with their valves. The glochidia remain attached to their fish host as parasites for approximately a month, at which time they have transformed into juvenile mussels. The juvenile mussels are released from their fish host and fall to the stream or riverbed as free-living mussels (McMahon 1991).
The Higgins eye mussel is bradytictic, or long-term brooding, meaning that females brood their young for an extended period of time before they are released (MN DNR). Spawning occurs in the summer and the glochidia are retained in the gills of the female through the winter. Higgins eye have been reported brooding glochidia between May-July and September (Coker et al., 1921Waller and Holland-Bartels 1988). It is unknown if Higgins eye brood young annually.
See 'Reproduction and Life History' section for information regarding reproductive life cycle.
Generally speaking mussels are long lived animals, often living for several decades (McMahon 1991).
The exact breeding season is unknown, but the closely related Lampsilis abrupta is gravid from September to June (Ortmann, 1919). Sexual maturity is reached in 6-12 years and an individual may live up to 50 years. From USFWS (2004): Early studies indicated that the sauger (Stizostedion canadense) and freshwater drum (Aplodinotus grunniens) were fish hosts for glochidia of L. higginsii (Surber, 1912; Wilson, 1916; Coker et al., 1921). These identifications were based on examination of natural infestations, but field identifications are not robust (Waller and Holland-Bartels, 1988; Waller and Mitchell, 1988); Hove and Kapuscinski (2002), however, confirmed sauger as a suitable host. Based on laboratory infestations of fish with L. higginsii glochidia, Waller and Holland-Bartels (1988) indicated that four species of fish were suitable hosts: largemouth bass (Micropterus salmoides), smallmouth bass (M. dolomieu), walleye (Stizostedion vitreum vitreum) and yellow perch (Perca flavescens). There was some transformation of glochidia to juveniles on green sunfish (Lepomis cyanellus), whereas two species, bluegill (Lepomis macrochirus) and northern pike (Esox lucius), were considered marginal hosts, because each produced only one juvenile. The common carp (Cyprinus carpio) and fathead minnow (Pimephales promelas) were unsuitable hosts. Studies by Waller and Holland-Bartels (1988) and Waller and Mitchell (1988) supported those by Sylvester et al. (1984) that walleye and largemouth bass were hosts for L. higginsii, but Sylvester et al. (1984) indicated that the green sunfish and bluegill were not suitable hosts. Hove and Kapuscinski (2002) confirmed largemouth bass as suitable hosts and found that sauger and black crappie also facilitated metamorphosis of L. higginsii glochidia. Lampsilis higginsii is a long-term brooder (bradytictic). Glochidial release has been reported during June and July and May and September. Glochidia of L. higginsii are morphologically similar to those of several other species of lampsilines in the Upper Mississippi River. Waller and Mitchell (1988) have shown that Lampsilis higginsii glochidia can be differentiated from L. cardium, L. siliquoidea, and Ligumia recta by electron microscopy; they could not be differentiated by light microscopy or morphometric measures.
Higgins eye reproduction is probably very similar to other native freshwater mussels. Male mussels release their sperm into the water, often in packets known as volvocoid bodies, which are taken by females through their incurrent apertures. Fertilization occurs and the fertilized eggs are brooded in the water tubes of the female's gills (McMahon 1991).
Molecular Biology and Genetics
There are 10 total barcode sequences available from GenBank (as of now BOLD has no entries for L. higginsii). Of the 10 barcode sequences 8 are of the cytochrome oxidase subunit 1 (CO1) barcode sequence and 2 are of the NADH dehydrongenase subunit 1(ND1) barcode sequence.
Following are the GenBank accession numbers for the CO1 region:
Following are the GenBank accession numbers for the ND1 region:
Barcode data: Lampsilis higginsii
No available public DNA sequences.
Download FASTA File
Statistics of barcoding coverage: Lampsilis higginsii
Public Records: 6
Specimens with Barcodes: 6
Species With Barcodes: 1
National NatureServe Conservation Status
Rounded National Status Rank: N1 - Critically Imperiled
NatureServe Conservation Status
Rounded Global Status Rank: G1 - Critically Imperiled
Reasons: Although never a common species, range has been reduced to a few remaining sites on the Mississippi River (a decline of over 50% recently and likely over 80% historically) and two tributaries (from 9 historically). Recent reintroduction and new populations have been discovered but zebra mussels (not a threat during initial conservation assessment of 1982) now pose a serious threat to many of the most viable populations and predictive models indicate futher decline, although some evidence of recovery in the presence of zebra mussels has been shown.
Intrinsic Vulnerability: Highly vulnerable
Comments: This species was never abundant to begin with plus has experienced some decline (USFWS, 2004), however, it has been shown to be adapted as a rare species even historically and, despite some early occurrences in smaller tributaries, is a large-river species and recently has shown some potential for recovery even in the presence of zebra mussels (Miller and Payne, 2007).
Environmental Specificity: Very narrow. Specialist or community with key requirements scarce.
Comments: The species is restricted to high flow conditions only primarily in large rivers (difficult to survey) and early occurrences in slower flowing smaller tributaries was represented by very small populations with poor or no viability (Miller and Payne, 2007).
Other Considerations: Zebra mussels are a serious threat now.
IUCN Red List Assessment
Red List Category
Red List Criteria
- Needs updating
- 1994Endangered(Groombridge 1994)
- 1990Endangered(IUCN 1990)
- 1988Endangered(IUCN Conservation Monitoring Centre 1988)
- 1986Endangered(IUCN Conservation Monitoring Centre 1986)
Date Listed: 06/14/1976
Lead Region: Great Lakes-Big Rivers Region (Region 3)
Where Listed: Entire
Population location: Entire
Listing status: E
For most current information and documents related to the conservation status and management of Lampsilis higginsii , see its USFWS Species Profile
Higgins eye was the first freshwater mussel to be granted protection as a federally endangered species in 1976. It has become rare or extirpated throughout its former range. It is estimated that the current range of the Higgins eye is half as large as its former range. Whereas it is used to be found in the Mississippi River as far south as Missouri, it's southern boundary is now the Lock and Dam 19 at Keokuk, Iowa (USFWS, USFWS 2004). Its range has also declined in many of the other rivers where it was found (Illinois, Sangamon, and Rock Rivers in Illinois, Iowa, Cedar, and Wapsipinicon Rivers in Iowa; Wisconsin and St. Croix Rivers in Wisconsin; and Minnesota River in Minnesota) (USFWS 2004).
Conservation efforts began in 1980 by a recovery team consisting of biologists from the U.S. Fish and Wildlife Service, Minnesota and Wisconsin Departments of Natural Resources, the U.S. Geological Survey, U.S. Army corps of Engineers, University of Minnesota, Macalester College, and Western Wisconsin Technical College. The group, named the Higgins Eye Pearlymussel Recovery Team, wrote the first recovery plan in 1983 and reconvened in 2004 to update the plan (USFWS, MN DNR). Parts of the plan involve protecting known Higgins eye locations, propagation and reintroduction of juvenile mussels, development of standardized sampling protocols to evaluate status of populations, determination and measurement of water quality criteria needed to sustain Higgins eye, and retrieving mussels from zebra mussel infested locations (USFWS 2004). Higgins eye is currently listed as endangered in Illinois, Iowa, Minnesota, Missouri, Nebraska, South Dakota, and Wisconsin.
Global Short Term Trend: Decline of 30-50%
Comments: It has been eliminated from approximately 45% of its original range. Thiel (1987) reported mid-1980's die-offs of mussels in the Mississippi River that were most noticeable in areas of Lampsilis higginsii occurrence. Cummings and Mayer (1997) noted it is extirpated from all other (5 total) drainages where it was historically found in Illinois except a few sites on the Mississippi River. Blodgett and Sparks (1987) noted a decline in the unionid community near the Sylvan Slough Essential Habitat Area and Havlik (1987) noted a die-off near Prairie du Chien, Wisconsin, another Essential Habitat Area. Havlik (1987) also indicated an unusual number of fresh-dead Lampsilis higginsii at this site in 1985. Few papers presented at a workshop examining die-offs (Neves, 1987) gave concrete reasons for the cause of the die-off, however Scholla et al. (1987) indicated that a gram-negative rod bacterium, which forms yellow colonies was associated with sick mussels from the Tennessee River. Latest recovery plan lists 10 (up from 7 in previous plan) locations as primary habitats (6 in Mississippi River between river miles 489 and 656, 1 in Wisconsin River, 3 in St. Croix River) and 9 (same as previous plan) as potential secondary habitats, with reintroductions since 2000 into 4 rivers from which it had previously been extirpated (USFWS, 2004). Data from Miller and Payne (2007) suggest the species may not be in imminent danger of extinction, has always been rare, and is not adapted to small rivers.
Global Long Term Trend: Decline of 70-90%
Comments: The Higgins eye pearlymussel was never abundant and Coker (1919) indicated that it was becoming increasingly rare even at the end of the 1800s. The fact that there were few records of live specimens from the early 1900s until the enactment of the Endangered Species Act in 1973 was a major factor in its listing in 1976; and historical and archaeological sites indicate the species has consistently been a rare component of the river fauna (Miller and Payne, 2007). Pre-1965 range was from Prescott, Wisconsin (RM 811) to Louisiana, Missouri (RM 283), a distance of 850 km (Havlik, 1981); as well as 9 tributaries (Minnesota River, Minnesota; St. Croix and Wisconsin Rivers, Wisconsin; Rock, Illinois, and Sangamon Rivers, Illinois; Wapsipinicon, Iowa, and Cedar Rivers, Iowa). After 1965, 196 and 248 km were lost from the northern and southern part of its range, respectively (overall decline of > 50%) and tributary occurrences declined from 9 to 2 (St. Croix and Wisconsin Rivers) (Havlik, 1981). Data from Miller and Payne (2007) suggest the species may not be in imminent danger of extinction, has always been rare, and is not adapted to small rivers.
Degree of Threat: High
Comments: Fuller (1978) suggested that overfishing may be at least in part responsible for the decline of this species. Based on collecting efforts with a commercial clamming operation in Prairie du Chien, Wisconsin, Mathiak (1979) estimated that hundreds were harvested in the years prior to the species' listing as an endangered species in 1976, likely leading to its eventual listing as an endangered species. Although zebra mussels are currently the most important threat (in all areas) to Lampsilis higginsii, habitat alteration (construction activities, channelization, sedimentation, dredging), environmental contaminants (spills, seasonal runoff flushings, sediments, agricultural runoff), other invasive species (black carp, round goby, and poor water quality may also pose significant threats (USFWS, 2004). Commercial harvest has been identified as a small historical threat only. Both recovery plans (USFWS, 1983; 2004) suggest the reduced range of the species could be attributed to anthropogenic impacts: increased sedimentation, river modifications, and poor water quality; as well as impact from zebra mussels, although it does have some capability of recovering from such infestations. Historical data do not provide clear evidence that stable, recruiting populations ever existed in the 7 tributaries where it has not been collected recently (Miller and Payne, 2007).
Restoration Potential: This species has received more conservation aid than any other mussel and is the subject of a federal recovery plan. It has been transplanted with at least initial success. Since the inception of the recovery plan, additional populations have been discovered, some containing numerous individuals. It has been suggested by some workers that it be delisted from the endangered status. Because of this attention, this species may be a good candidate for man-mediated recovery and conservation within its remaining range.
Management Requirements: Refer to the General Freshwater Mussel ESA.
Monitoring Programs: Oblad (1980) and Nelson (1982) reported on a relocation effort for L. HIGGINSI. That species was recovered by brail in an area scheduled for the construction of a new bridge at Moline, IL. Some 7,000 mussels were collected by divers and marked with monofilament tags and/or paint. Of these 7,000, three were individuals of L. HIGGINSI, two males and one female. All mussels were transplanted 1/4 mile upstream into the same mussel bed along a transect line. A year later, all three L. HIGGINSI were recovered alive and apparently healthy. It is unknown if the mussels have, or will, reproduce or if the fish host (unknown) is present. It is felt that at least 8-10 years of monitoring would be necessary to determine if the transplant was a success in the long term. There are no such plans to continue the project.
Stern (1982), leader of the U.S. Fish and Wildlife Higgin's Eye Recovery Plan, has outlined the project. The aims of the project are to establish a minimum of five viable, reproducing populations and to minimize environmental impacts. He defines a viable, reproducing population as one having equal or greater recruitment than mortality. Of the 17 initially potential sites, seven were suitable for transplanting. Because so little is known concerning the habitat requirements of this species, the sites were chosen in part because of associated naiads. Nelson and Freitag (1980) noted that in over 50% of the collection records, Higgin's eye was associated with 17 more common species. The ongoing project will monitor the species for 1) viable glochidia; 2) presence of host fish, believed to be the Sauger and Freshwater drum; 3) successful establishment of metamorphosed juveniles; and 4) presence of several age classes.
Management Research Programs: Refer to the General Freshwater Mussel ESA.
Biological Research Needs: Relocation and translocation away from zebra mussels. Develop propagation techniques.
Global Protection: Few (1-3) occurrences appropriately protected and managed
Comments: Since 2000, a propagation program has been rearing this species in the Genoa National Fish Hatchery in Wisconsin for release into the wild (22,000 individuals scheduled for fall 2007 release) and 3500 host fish (walleye, largemouth bass, and smaillmouth bass) have been reared annually and released into the Wisconsin, Iowa, and Wapisipincon Rivers (Springer, 2007). The species has been recently released (2000-2003) in approximately 37 sites in 7 rivers (Upper Mississippi River, St. Croix, Wisconsin, Wapsipinicon, Cedar, Iowa, and Black Rivers) (USFWS, 2004). In 2001 this species was found alive at four sites in the Upper Mississippi River National Wildlife and Fish Refuge (formerly Savanna Army Depot) in Illinois/Iowa between RM 544.5 and 558.4 in relative abundance from 0.9 to 2.6% (Sietman et al., 2004).
Needs: The removal of zebra mussels in a manner and scale necessary to benefit L. higginsii is evidently not currently feasible. Therefore, the plan focuses on developing methods to prevent new infestations, monitoring zebra mussels at Essential Habitat Areas, and developing and implementing contingency plans to alleviate impacts to infested populations. Based on recent activities, the latter may consist largely of removing L. higginsii from areas where zebra mussels pose an imminent risk to the persistence of the population and releasing them into suitable habitats within their historical range where zebra mussels are not an imminent threat. Because this is a species that is widespread but uncommon, it can be best protected by implementing conservation strategies that safeguard rich and diverse mussel assemblages and the habitats upon which they depend, as opposed to conservation at the species level (Miller and Payne, 2007).
Federal management of the species follows the Recovery Plan for the species (USFWS 2004).
Relevance to Humans and Ecosystems
Stewardship Overview: This species was listed as federally endangered in the U.S. in 1976 and a recovery plan (USFWS, 2004) created. Reintroductions have occurred since 2000 into 4 rivers from which it had previously been extirpated (USFWS, 2004), including pool 4 and the Twin Cities region nof the Mississippi River below St. Anthony Falls, Minnesota (Sietman, 2003). The first recovery plan (USFWS, 1983) included six locations in the Upper Mississippi River and one in the St. Croix River as essential habitats because they supported viable reproductive populations and the second recovery plan (USFWS, 2004) identified 3 more (1 in the Wisconsin River and 2 in the St. Croix River), identifying these regions as "Essential Habitat Areas (EHA). EHAs are those sites with at least 0.25% of the mussel fauna identified as Lampsilis higginsii, a dense assemblage (>10/ square meter), and contained at least 15 species (each > 0.01/square meter). The plan recommended downlisting to threatened if populations in 5 EHAs were reprducing, self-sustaining, and not threatened by zebra mussels; and delisted if populations in 5 EHAs met the above criteria and were sufficiently secure to assure long-term viability.
Higgins' eye pearly mussel
Lampsilis higginsii is a rare species of freshwater mussel known by the common name Higgins' eye pearly mussel. It is native to the United States, where it occurs in the Mississippi River and the drainages of some of its tributaries. It is threatened by the introduced zebra mussel (Dreissena polymorpha). It is a federally listed endangered species of the United States.
This bivalve mollusc is in the family Unionidae, the river mussels. It is oval in shape with a thick, heavy shell which is yellowish or brown, sometimes with greenish rays. It reaches up to 10.2 centimeters in length (between 4-5 inches). The nacre is white, sometimes tinged pink and partly iridescent.
The historical range of this species stretched along 850 kilometers (about 520 miles) of the Mississippi River from Prescott, Wisconsin, to Louisiana, Missouri, as well as nine tributaries of the Mississippi. Today it can be found in the Mississippi from La Crosse, Wisconsin, to Muscatine, Iowa, and two tributaries, the St. Croix and Wisconsin Rivers. It has always been rare, but it experienced a large reduction in population after 1965, when it began to lose the northernmost and southernmost reaches of its distribution, a total of over 50% of its range. One cause of the drop in population was pollution. The mussel is now extirpated from the Illinois River because of pollution. The habitat has been altered by impoundments, including dams and locks. Sedimentation may also have negatively affected the mussel. Overfishing may have reduced the population, as well.
Today the worst threat to the species is the invasive species invasion of the zebra mussel. Zebra mussels attach to the shells of this and other native mussels, deforming them, preventing them from moving, and preventing their filter feeding. The zebra mussels can use up all the food in the vicinity and deplete the oxygen, and may also consume the native mussels' larvae and sperm, preventing reproduction. Deposits of waste products degrade the habitat. Other invasive species include the Asian clam (Corbicula fluminea), which competes with the native mussel and consumes its sperm, larvae, and juveniles. Some introduced species of fish may eat juvenile mussels.
During breeding, the male releases sperm and the female siphons it and keeps the fertilized eggs in her gills until they hatch. The glochidia, or mussel larvae, are released and enter the bodies of host organisms, which are fish. Some fish hosts for the mussel are largemouth bass (Micropterus salmoides), smallmouth bass (M. dolomieu), walleye (Sander vitreus), and yellow perch (Perca flavescens).
This mussel has been propagated in captivity and released into appropriate habitat in areas where it has been extirpated.
References[edit source | edit]
- Lampsilis higginsii. The Nature Conservancy.
- Miller, A. C. and B. S. Payne. (2007). A re-examination of the endangered Higgins eye pearlymussel Lampsilis higginsii in the upper Mississippi River, USA. Endang Species Res 3 229-37.
- Lampsilis higginsii. Illinois Natural History Survey.
- USFWS. Lampsilis higginsii Five-year Review. May 2006.
- USFWS. Lampsilis higginsii Life History.