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Recovery Strategy For Northern Riffleshell, Snuffbox, Round Pigtoe, Mudpuppy Mussel and Rayed Bean in Canada [Proposed]

4. Species Information: Mudpuppy Mussel

Common Name1: Mudpuppy Mussel

Scientific Name: Simpsonaias ambigua

Assessment Summary

 Status: Endangered

Reason for designation: The Mudpuppy Mussel has suffered declines in their range and the population is extremely fragmented. In Canada, there are only three extant sites remaining, all of which are in the Sydenham River.  The Mudpuppy Mussel is host specific, using only the mudpuppy (Necturus maculosis) as host. Any threats to the mudpuppy are also threats to mussels.

Occurrence: Ontario

Status history: designated endangered in 2001

 1This species is also known as the Salamander Mussel.

Figure 10. The mudpuppy Mussel (Simpsonaias ambigua). Photo credit : D. Zanatta, University of Toronto

The Mudpuppy Mussel is a small freshwater mussel that is distinguished from other mussels by its elongate elliptical shell shape, incomplete hinge teeth, double-looped beak sculpture, and rayless, brown periostracum. The shell is thin, fragile, and compressed in males to slightly inflated posteriorly in females.  It is much thicker anteriorly than posteriorly.  The anterior and posterior ends are rounded; the dorsal and ventral margins are nearly straight and parallel.  The posterior ridge is rounded.  The beaks are located approximately one-quarter of the distance from anterior to posterior, and are slightly elevated above the hinge line and somewhat compressed.  Beak sculpture consists of four to five double-looped ridges.  The periostracum (shell surface) is smooth, yellowish tan to dark brown in colour, and rayless.  Pseudocardinal teeth are very small, low, and rounded - one in each valve.  Lateral teeth are absent (Watson et al.2001b).

Historically, the Mudpuppy Mussel was known from Arkansas, Illinois, Indiana, Iowa, Kentucky, Michigan, Minnesota, Missouri, New York, Ohio, Pennsylvania, Tennessee, West Virginia, Wisconsin, and Ontario (TNC 2000a).  It was found in the Lake St. Clair, Lake Huron, and Lake Erie drainages as well as the Ohio, Cumberland, and upper Mississippi river systems (Clarke 1985).  In Ontario, only three historical records exist for this species, two from the Sydenham River in the 1960s and one from the Detroit River in 1934.

In the United States, the Mudpuppy Mussel is now thought to be extant in only 32 of the 80 rivers and streams for which historical records are available.  It is believed to be extirpated from Iowa, New York and Tennessee. The Nature Conservancy has assignedthis species a global rank of G3 (rare and uncommon globally), and an SRANK of S1 in six states and S2 in four others (TNC 2000a).  The species is listed as endangered in Illinois, Michigan, and Tennessee; threatened in Minnesota, Ohio, and Wisconsin; and of Special Concern in Indiana.

In Ontario, the Mudpuppy Mussel had been ranked SH (historical; no occurrences verified in the past 20 years) until the late 1990s by the Ontario Natural Heritage Information Centre.  Intensive surveys conducted on tributaries to Lake Erie, Lake St. Clair and lower Lake Huron in 1997-1999 (Metcalfe-Smith et al. 1998, 1999) produced a total of 90 specimens from 8 different sites on the Sydenham River and one site on the Thames River. The current distribution of the Mudpuppy Mussel in Ontario is likely restricted to the middle reach of the East Sydenham River, although a single fresh valve was reported from the Thames River in 1998.  Based on these findings, the Mudpuppy Mussel was downlisted from SH to S1 in Ontario.

The Mudpuppy Mussel occurs in the most heavily populated and intensively farmed region of Canada, notably southwestern Ontario. Agricultural, urban, and industrial impacts have likely resulted in a loss of habitat forthis species in the Sydenham and Thames rivers.  Urban impacts on the East Sydenham River are less than in other southwestern Ontario rivers, and water quality may have improved in recent years due to an improvement in sewage treatment.  Agricultural activities have increased, however, and run-off of silt and agricultural chemicals may continue to limit the distribution of the Mudpuppy Mussel in this system (Dextrase et al. 2003). 

Distribution

GlobalRange: The Mudpuppy Mussel currently occurs in Arkansas, Illinois, Indiana, Kentucky, Minnesota, Missouri, Ohio, Pennsylvania, West Virginia, Wisconsin, and Ontario.

CanadianRange: There are only three historical records for the Mudpuppy Mussel in Canada, two from the Sydenham River in the mid 1960s and one from the Detroit River in 1934. The Mudpuppy Mussel currently occurs only in the East Sydenham River in Ontario, although a single fresh valve was found on the Thames River in the city of London in 1998. It has been suggested that the Mudpuppy Mussel isat the northern most limit of its range in the Great Lakes region and may be naturally rare here.

Figure 11. Global distribution of the Mudpuppy Mussel.

Figure 11. Global distribution of the Mudpuppy Mussel.

Figure 12. Distribution of the Mudpuppy Mussel in Canada.

Figure 12. Distribution of the Mudpuppy Mussel in Canada.

Percent of Global Range in Canada:Less than 5% of the species’ global distribution is currently found in Canada.

Distribution Trend:The Mudpuppy Mussel is no longer found in 60% of formerly occupied rivers and streams in the United States and is extirpated from Iowa, New York, Tennessee, and Michigan. In Canada, it was historically known from the Detroit and Sydenham rivers, but recent surveys in both rivers show that it now occurs only in the Sydenham River. Live animals were collected from eight different sites within a 50-km reach of the East Sydenham River in 1997-1999. The broad range of sizes of live specimens and fresh shells indicated that there is ongoing recruitment.

Population Abundance

Global Range: In the United States, extant populations are known from 11 states and its range appears to be declining in most jurisdictions. The     Mudpuppy Mussel is thought to be present in only 32 of the 80 rivers and streams for which historical records are available.

CanadianRange: Intensive surveys conducted at 66 sites on tributaries to Lake Erie, Lake St. Clair and lower Lake Huron in 1997-1998 (Metcalfe-Smith et al. 1998, 1999), and additional collections at some of these sites in 1998 and 1999, yielded a total of 90 specimens from 8 different sites on the Sydenham River and one site on the Thames River.

Percent of Global Abundance in Canada:  Less than 5% of the species’ global distribution is currently found in Canada. Population abundance estimates are not available.

Population Trend: The Mudpuppy Mussel is no longer found in 60% of formerly occupied rivers and streams in the United States and is extirpated from Iowa, New York, Tennessee, and Michigan. In Canada, it was historically known from the Detroit and Sydenham rivers, but recent surveys in both rivers show that it now occurs only in the Sydenham River. Live animals were collected from eight different sites within a 50-km reach of the East Sydenham River in 1997-1999. The broad range of sizes of live specimens and fresh shells indicated that there is ongoing recruitment.

Biological Limiting Factors

Reproductive Attributes: Although the reproductive biology of the Mudpuppy Mussel follows the general reproductive biology of most mussels, this species is unique in the fact that it is the only species to use a host other than a fish. During spawning, male mussels release sperm into the water column and females filter it out of the water with their gills. Fertilization is then able to occur in specialized regions of the gills known as marsupia and are released by the female into the water column to undergo a period of parasitism on a suitable host species. Further development to the juvenile stage can not continue without a period of encystment on the host. The glochidia of the Mudpuppy Mussel have hooks that likely ensure a firm attachment to the external gills of their host. After they have attached to a host, the glochidia become completely encysted within 36 hours.  Once encystment on a suitable host occurs, it may take from 6 days to over 6 months to complete the transformation from glochidium to juvenile mussel (Kat 1984).  During this period, the glochidium is parasitic. Once metamorphosis is complete, the juvenile mussel ruptures the cyst by extending its foot (Lefevre and Curtis 1910).  The mudpuppy, Necturus maculosus, is the only known host for the Mudpuppy Mussel. The mudpuppy is broadly distributed in lakes and rivers throughout Quebec, Ontario and Manitoba. The mudpuppy inhabits areas with flat rocks, submerged logs, wooden slabs and other debris. The habitat requirements of the mudpuppy host correspond with the habitat characteristics typically assigned to the Mudpuppy Mussel.

Dispersal: Like most freshwater mussels, the Mudpuppy Mussel has very limited dispersal abilities. The Mudpuppy Mussel adults are essentially sessile with movement limited to only a few meters on the river/lake bottom. Although adult movement can be directed upstream or downstream, studies have found a net downstream movement through time (Balfour and Smock 1995; Villella et al.2004). The primary means for large scale dispersal, upstream movement, and the invasion of new habitat or evasion of deteriorating habitat, is limited to the encysted glochidial stage on the host species.