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Recovery Strategy for the Northern Riffleshell, Snuffbox, Round Pigtoe, Mudpuppy Mussel and Rayed Bean in Canada (Final)


2. Species Information – Snuffbox


Common Name: Snuffbox

Scientific Name: Epioblasma triquetra

COSEWIC Status: Endangered

COSEWIC Reason for designation1: This species has been lost from 60% of its former range in North America. Remaining populations are fragmented, and most are in decline. In Canada, it is now restricted to a 50-km reach of the East Sydenham River. This population represents one of only about 50 extant occurrences in North America.

Occurrence: Ontario

COSEWIC Status history: Designated Endangered in 2001

1 A small, reproducing population has been confirmed in the Ausable River since the time of listing.

The Snuffbox does not closely resemble any other mussel in Canada (Clarke, 1981). The shell is solid, thick, and triangular in males, somewhat elongate in females. The anterior end is rounded and the posterior end is truncated in males, expanded in females. The ventral margin is slightly curved in males and almost straight in females. The dorsal margin is short and straight. The posterior ridge is high and sharply angled, extended posterioventrally in females. The posterior slope is wide, expanded and sculptured with radial, wavy ribs. The umbos are swollen and elevated above the hinge line, and they turn inward and anteriorly. The beaks are located anterior to the middle of the shell and have a sculpture consisting of three or four faint, double-looped ridges The shell is yellowish to yellowish green, and is marked with numerous dark green rays that are often broken, appearing as triangular or chevron-shaped spots. The shell surface is smooth (excluding the posterior slope), except for occasional concentric growth rests. Each valve has two pseudocardinal teeth that are ragged, compressed and relatively thin. There two lateral teeth in the left valve and one in the right are short, straight, elevated and serrated (Watson et al. 2001a).

Figure 4. The Snuffbox mussel Epioblasma triquetra. Photo courtesy S. Staton, Environment Canada.
Figure 4. The Snuffbox mussel Epioblasma triquetra. Photo courtesy S. Staton, Environment Canada.

Historically it was known to occur in 18 states throughout the Ohio-Mississippi River drainage and in the Great Lakes drainage in Lake Erie, Lake St. Clair, and tributaries to lakes Erie, St. Clair, Huron and Michigan. In Canada, the Snuffbox was only ever known from Ontario in the Ausable, Grand, Niagara, Sydenham and Thames rivers, Lake St. Clair, and Lake Erie. The distribution of the Snuffbox has become significantly reduced throughout its range. In the United States, it is no longer found in 60% of formerly occupied streams. Remaining populations are small and geographically isolated from one another, and not all of them are healthy and reproducing. The species has probably been extirpated from Iowa, Kansas, New York and Mississippi. Although it is not federally listed in the United States, it is listed as endangered or threatened in many states. The Nature Conservancy has assigned it a Global Rank of G3 (rare and uncommon globally), and it has an SRANK of S1 (very rare) in 10 states and Ontario. In Canada, there are 31 known historical records for the Snuffbox. Intensive surveys were conducted in 1997-1998 throughout its historical range and only seven live animals were found within a 50 km reach of the East Sydenham River between Alvinston and Dawn Mills (Metcalfe-Smith 1999). From 2001 – 2004, sections of the East Sydenham River were intensively surveyed again and the total number of live animals captured was 116 (McNichols and Mackie2004). In July 2003, a single live juvenile was found in the lower reaches of the main Ausable River below the Arkona Gorge. Ongoing surveys in 2006 have uncovered 14 live specimens, including numerous juveniles, from the area of the 2003 discovery. Densities at this site average 0.3 animals/m² ranging from 0-4 /m². These surveys have also detected a single live immature animal at a site well upstream near the town of Nairn (pers. comm. S. Staton, Fisheries and Oceans Canada). These recent findings suggest that the Ausable River still supports a reproducing population.

Agricultural, urban, and industrial impacts have likely resulted in a loss of habitat forthis species in the Ausable, Grand, 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 Snuffbox in this system (Dextrase et al. 2003).

Distribution

Global Range

The Snuffbox currently occurs in Alabama, Arkansas, Illinois, Indiana, Kentucky, Michigan, Minnesota, Mississippi, Missouri, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia, Wisconsin, and Ontario. In the United States, the Snuffbox is thought to be extant in only 37 of the 99 streams for which historical records are available (Watson et al. 2001a).

Canadian Range

In Canada, the Snuffbox was historically known from the Province of Ontario in the Ausable, Grand, Niagara, Sydenham and Thames rivers, Lake St. Clair, and Lake Erie (Watson et al. 2001a). Until recently, it was thought the only remaining population of the Snuffbox was in the East Sydenham River. However, a live juvenile was found in July 2003 by a Fisheries and Oceans Canada biologist in the lower reaches of the main Ausable River below the Arkona Gorge (ARRT 2005). Detailed sampling at this site in 2006 has demonstrated reproduction is occurring in the lower Ausable watershed and also produced evidence of recent reproduction at an additional site in the upper watershed near Nairn.

Percent of Global Range in Canada

Less than 5% of the species' global distribution is found in Canada.

Figure 5. Global distribution of the Snuffbox.
Figure 5. Global distribution of the Snuffbox.

 

Figure 6. Distribution of the Snuffbox in Canada
Figure 6. Distribution of the Snuffbox in Canada.

Distribution Trend

The range of the Snuffbox has been significantly reduced as it has been extirpated from Iowa and Kansas and probably New York. It is also believed to be extirpated from the Grand, Niagara and Thames rivers, Lake Erie and Lake St. Clair. The rate of change in geographical distribution is not available, but it has been lost from 60% of formerly occupied streams.

Population Abundance

Global Range

No abundance estimates are available for the global population (Dextrase et al. 2003). The Snuffbox typically occurs in low numbers in mussel communities where it is found, but it can be locally abundant. The Snuffbox is typically found at very low densities, representing <1% of the mussel assemblage. The largest remaining population in North America is found in the Clinton River, Michigan, where it was the dominant species in 1992. It is estimated that there are fewer than 50 reproducing, extant occurrences of the Snuffbox in North America (TNC 2000b). Most populations have become small and geographically isolated from one another. The Snuffbox has been extirpated from Iowa, Kansas and New York.

Canadian Range

The Snuffbox is currently known to occur only in a 50 km reach of the Sydenham River as well as at three sites within a 60 km reach of the Ausable River. It has likely been extirpated from the Grand, Thames, Detroit and St. Clair Rivers and Lakes Erie and St. Clair. Metcalfe-Smith et al. (1998, 1999) surveyed 17 sites on the Sydenham River in 1997-1998. Since 1997 123 live animals have been found in the Sydenham River (Metcalfe-Smith et al. 1998; Metcalfe-Smith et al. 1999; McNichols and Mackie 2004) while 15 live animals have been found in the Ausable (pers. comm. S. Staton, Fisheries and Oceans Canada).

Percent of Global Abundance in Canada

Global population abundance estimates are not available but the Canadian populations likely represent less than 5% of the global abundance.

Population Trend

It is difficult to determine if there have been changes over time in the abundance of Snuffbox in the Sydenham River, because so few live animals have ever been collected. Current and historical catch rates show a decline between 1963-1973 and 1997-1999 (Watson et al. 2001a). No data are currently available for the Ausable River population.

Biological Limiting Factors

Reproductive Attributes

The reproductive biology of the Snuffbox follows the general reproductive biology of most mussels. 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. Immature juveniles, known as glochidia, develop in the gill marsupia and are released by the female into the water column to undergo a period of parasitism on a suitable host fish species. The Snuffbox is a long-term brooder as fertilization occurs in late summer and glochidia are held by the female over winter for release the following spring or summer. Development to the juvenile stage can not continue without a period of encystment on the host. Female Snuffbox have developed specialized structures including a mantle lure and shell denticles which permit a unique method of host capture increasing the likelihood of successful encystment.

Until recently, the blackside darter and logperch (Percina caprodes) have been considered as the only fish hosts for the Snuffbox in Ontario (Watson et al. 2001a). To positively determine host fishes for the Snuffbox, sixteen host species underwent infestation experiments in the laboratory at the University of Guelph from 2002 – 2005. The Snuffbox successfully transformed on six of these: the Iowa darter, logperch, rainbow darter, mottled sculpin, largemouth bass (Micropterus salmoides) and brook stickleback (Culaea inconstans) although the logperch is considered to be the primary host (McNichols and Mackie 2002; McNichols et al. 2004).

Glochidia of all members of the genus Epioblasma, are morphologically depressed (where valve height is equal to or less than valve length). These glochidia are less likely to make initial contact with a host than elongate glochidia due to a smaller valve gape, but are better adapted to holding on tightly once contact has been made (Hoggarth 1993). It is likely that species with morphologically depressed glochidia have a lower rate of recruitment, and be more at risk of extinction once numbers of breeding adults reach a critical threshold level. Species of the genus Epioblasma have hookless glochidia and are gill parasites.

Dispersal

Like most freshwater mussels, the Snuffbox has very limited dispersal abilities. The Snuffbox 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 fish.