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Recovery Strategy for the Round Hickorynut (Obovaria subrotunda, Rafinesque 1820) and Kidneyshell (Ptychobranchus fasciolaris, Rafinesque 1820) in Canada [Proposed]


I. Background

  1. Species Information – Round Hyckorynut
  2. Species Information – Kidneyshell
  3. Threats
  4. Habitat – Round Hyckorynut
  5. Habitat – Kidneyshell
  6. Habitat Trend
  7. Habitat Protection
  8. Ecological Role
  9. Importance to People
  10. Knowledge Gaps
  11. Biological and Technical Feasibility of Recovery

1. Species Information – Round Hickorynut

COSEWIC Assessment Summary: May 2003

Common Name: Round Hickorynut

Scientific Name: Obovaria subrotunda

COSEWIC Status: Endangered

COSEWIC Reason for designation: This species has been lost from 90% of its former range in Canada. Populations in the Grand and Thames rivers are extirpated and populations in the Sydenham River are declining, all due to the combined effects of pollution and agricultural impacts. Most of the Great Lakes populations have been lost due to impacts of the zebra mussel, and the remaining population in the St. Clair delta near Walpole Island may be at risk. If the Eastern Sand Darter were the host of this species, then the decline of this threatened fish would affect the mussel's survival.

Occurrence: Ontario

COSEWIC Status history: Designated Endangered in 2003.

The Round Hickorynut is one of only 6 species in the genus Obovaria. Only two of these species, O. subrotunda, and O. olivaria, have distributions which extend into Canada where both species are restricted to the Lower Great Lakes/St. Lawrence River drainage. The Round Hickorynut is considered globally secure (G4) and nationally secure (N4) within the United States although the American Fisheries Society has listed it as a species of special concern. The species is beginning to show declines across its entire American distribution. It is considered endangered within Michigan and is believed to be extirpated from Illinois (G. Kruse, Illinois Department of Natural Resources, pers. comm. February, 2004)) and New York (D. Strayer, Institute of Ecosystem Studies, pers. comm., February 2004). In Canada, the Round Hickorynut is considered critically imperiled (N1) and was designated as endangered by the Committee on the Status of Endangered Wildlife in Canada in 2003. The Canadian distribution of this species has always been restricted to southwestern Ontario where it was once found in the Welland, Grand, Sydenham, Thames, St. Clair and Detroit Rivers as well as the waters of Lake St. Clair and western Lake Erie. Declining water quality and the introduction of dreissenid mussels have resulted in a sharp decline in the Canadian distribution of the Round Hickorynut and it is now only found in the waters of the Lake St. Clair delta and a small portion of the East Sydenham River.

The Round Hickorynut is a small mussel reaching a maximum size of 60 - 65 mm in Canada. The mussel is readily recognized by its round shape and prominent centrally located, inward curving beaks that are elevated well above the hinge line. Beak sculpture is slight, consisting of 4 to 5 weak double bars which are sinuous centrally and angled posteriorly (Parmalee and Bogan 1998). The shell is generally dark in colour ranging from olive-brown to dark brown and is relatively smooth except for prominent growth rests. The posterior slope is often distinctly lighter than the rest of the shell (COSEWIC 2003a) (Figure 1). The hinge teeth of this species are heavy and strong. The left valve has two thick, roughened, triangular pseudocardinal teeth and two slightly curved, short, strong lateral teeth. The right valve has one large, massive serrated triangular pseudocardinal tooth, usually with a small, low compressed tubercular tooth on either side. There is one short, curved, thick, roughened lateral tooth and often an incomplete secondary lateral tooth in the right valve (Parmalee and Bogan 1988).

Figure 1: Two Round Hickorynut specimens from the Lake St. Clair delta. Note the characteristic lightening of the posterior slope. Photo credit: D. McGoldrick, Environment Canada.
Figure 1: Two Round Hickorynut specimens from the Lake St. Clair delta. Note the characteristic lightening of the posterior slope. Photo credit: D. McGoldrick, Environment Canada.

Distribution

Global Range

The global distribution of the Round Hickorynut is restricted to eastern North America (Figure 2). In the United States the Round Hickorynut is considered nationally secure but is showing declines across its range. This species is historically known from the Ohio, Tennessee, Cumberland and Mississippi River systems as well as the St. Lawrence, Lake Erie and Lake St. Clair drainages. It is currently found in Alabama, Indiana, Kentucky, Michigan, Mississippi, Ohio, Pennsylvania, Tenessee and West Virginia and is believed to have been extirpated from New York and Illinois. In Canada the Round Hickorynut is considered critically imperiled, classified as endangered by COSEWIC and found only in southwestern Ontario.

Figure 2: Global distribution of the Round Hickorynut (modified from Parmalee and Bogan 1998)
Figure 2: Global distribution of the Round Hickorynut (modified from Parmalee and Bogan 1998)

Canadian Range

In Canada, the Round Hickorynut is historically known from the waters of western Lake Erie, Lake St. Clair and the Welland, Grand, Thames, Sydenham and Detroit Rivers (COSEWIC 2003a). Since 1996, live specimens have only been reported from the Sydenham River and Lake St. Clair (Figure 3).

Figure 3: Distribution of the Round Hickorynut in Canada. Current distribution reflects surveys since 1996.
Figure 3: Distribution of the Round Hickorynut in Canada. Current distribution reflects surveys since 1996.

Percent of Global Range in Canada

Approximately 1% of the global range of this species occurs in Canada.

Distribution Trend

Since the invasion of the Great Lakes by dreissenid mussels the Canadian geographical distribution for this species has been reduced by 90%.

Population Abundance

Global Range

In the United States the Round Hickorynut is seldom a significant component of the mussel community, typically representing between 0.1 and 1.4% of the species present (COSEWIC 2003a).

Canadian Range

The largest Canadian population of the Round Hickorynut occurs in the delta region of Lake St. Clair where it comprises 0.011% of the overall mussel community and occurs at a density of 0.0006/m². In the Sydenham River the Round Hickorynut represents approximately 0.0024% of the mussel community.

Percent of Global Abundance in Canada

Less than 1% of the global abundance of this species occurs in Canada.

Population Trend

It is estimated that the population of Round Hickorynut in Canada has declined by 90% since the invasion of the Great Lakes by dreissenid mussels. This estimate is based on the number of historical records that occur in waters that now contain dreissenid mussels.

Biological Limiting Factors

Reproductive Attributes

The reproductive biology of the Round Hickorynut follows the general reproductive biology of most unionid 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. Further development to the juvenile stage can not continue without a period of encystment on the host. The hookless glochidia become encysted on the gills of the host and are encapsulated in a fluid filled sac where they are nourished by the host until they metamorphose and break free, settling to the substrate to begin life as free-living juveniles. The host fish species for the Round Hickorynut has not been confirmed for Canadian populations although 5 host species have been identified in the United States. These 5 species include: varigate darter (Etheostoma variatum); frecklebelly darter (Percina stictogaster); speckled darter (E. stigmaeum); greenside darter (E. blennioides); and emerald darter (E. baileyi) (M. McGregor, Kentucky Department of Fish and Wildlife Resources, pers. comm., January 2004). Only the greenside darter is found in Canada where its range appears to be expanding. Interestingly, the known current and historic range of the greenside darter does not completely overlap with the historic range of the Round Hickorynut (i.e., greenside darters are not known from the Grand River prior to 1990 and no records exist for this species from the Welland River or Lake Erie (A. Dextrase, Ontario Ministry of Natural Resources, Peterborough, pers. comm.)) suggesting the existence of an additional host. Round Hickorynuts are known to be gravid between September and June and may be using host fish during this time.

Dispersal

Like most native freshwater mussels, Round Hickorynut 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.

2. Species information – Kidneyshell

COSEWIC Assessment Summary: May 2003

Common Name: Kidneyshell

Scientific Name: Ptychobranchus fasciolaris

COSEWIC Status: Endangered

COSEWIC Reason for designation: This species has been lost from about 70% of its historical range in Canada due to impacts of the zebra mussel and land use practices. It is now restricted to the East Sydenham and Ausable rivers. Although both populations appear to be reproducing, there is evidence that abundance has declined in the East Sydenham River. Agricultural impacts, including siltation, have eliminated populations in the Grand and Thames rivers, and threaten the continued existence of this species in Canada.

Occurrence: Ontario

COSEWIC Status history: Designated Endangered in 2003.

The Kidneyshell (Figure 4) is one of 5 members of the genus Ptychobranchus that occur in North America, however, it is the only member of the genus with a distribution that extends into Canada. The species is considered globally secure (G4) and is listed by the American Fisheries Society as being stable within the United States although, in Canada, the Kidneyshell was designated as endangered by COSEWIC in 2003. The Kidneyshell has always had a Canadian distribution limited to southwestern Ontario where it was once found in lakes St. Clair and Erie, as well as the Detroit, Sydenham, Thames, Ausable, Grand, Welland and Niagara rivers. Recent surveys have shown that this distribution has been reduced and the Kidneyshell is now limited to the Sydenham and Ausable rivers with a few scattered specimens in the Lake St. Clair delta.

The Kidneyshell is a medium to large freshwater mussel that is readily distinguished by its elongate, elliptical shell and yellowish-brown periostracum with wide, interrupted green rays that look like squarish spots (Figure 4). The type locality is the Muskingham River, Ohio. The following description of the species, reported in COSEWIC (2003b), was adapted from Clarke (1981), Strayer and Jirka (1997) and Parmalee and Bogan (1998). The shell is solid, heavy and compressed, and may have a humped shape in old individuals. The anterior end is rounded and the posterior end is bluntly pointed. Beak sculpture is poorly developed, consisting of several fine, indistinct wavy ridges. The surface of the shell (periostracum) ranges in colour from yellowish to yellowish-green, yellowish-brown, or medium brown, with generally distributed broad, interrupted green rays; the shells of old specimens may be a dark chestnut brown and rayless. The periostracum is unsculptured except for coarse growth rests and a roughened posterior slope. The nacre is generally white or bluish white, but may be pinkish in young specimens. The hinge teeth are heavy. The left valve has two low, thick, serrated triangular pseudocardinal teeth and two lateral teeth that are short, nearly straight, and usually widely separated. The right valve has one somewhat compressed and pyramidal elevated tooth and one wide, elongated and serrated lateral tooth. The lateral teeth are almost pendulous distally, which is a good distinguishing feature. The interdentum is wide and the beak cavity is shallow. Females have a conspicuous groove on the inside of the shell that runs diagonally from the beak cavity towards the posterioventral end; this groove corresponds to the marsupium (COSEWIC 2003b).

Figure 4: Two kidneyshell specimens from the Sydenham River. Note the characteristic squarish spots. Photo credit: T. Morris, Fisheries and Oceans Canada.
Figure 4: Two kidneyshell specimens from the Sydenham River. Note the characteristic squarish spots. Photo credit: T. Morris, Fisheries and Oceans Canada.

Distribution

Global Range

In the United States, the Kidneyshell is currently found in Ohio, Tennessee, Kentucky, Michigan, New York, Pennsylvania, West Virginia, Virginia, Alabama, Mississippi and Illinois.

Figure 5: Global distribution of the Kidneyshell (modified from Parmalee and Bogan 1998)
Figure 5: Global distribution of the Kidneyshell (modified from Parmalee and Bogan 1998)

Canadian Range

In Canada, the Kidneyshell is found only in southwestern Ontario. Since 1997, live specimens have only been reported from the Ausable River, Sydenham River, and Lake St. Clair.

Figure 6: Distribution of the Kidneyshell in Canada. Current distribution reflects surveys since 1997.
Figure 6: Distribution of the Kidneyshell in Canada. Current distribution reflects surveys since 1997.

Percent of Global Range in Canada

Less than 5% of the global range of this species occurs in Canada.

Distribution Trend

Since the invasion of the Great Lakes by dreissenid mussels the Canadian geographical distribution for this species has been reduced by 70%.

Population Abundance

Global Range

In the United States the Kidneyshell is seldom a significant component of the mussel community but may be locally abundant. It usually represents on average 2.5% (0.2-8.0%) of the mussel community in rivers but at individual sites where it is found the Kidneyshell may account for more than 10% of the community.

Canadian Range

The largest Canadian population of the Kidneyshell occurs in the Ausable River where it comprises 1.5% of the overall mussel community. In the Sydenham River it occurs in an average estimated density of 0.12/m² at sites where it was found alive. In the Lake St. Clair delta Kidneyshells comprised only 0.3% of the overall mussel community (COSEWIC 2003b).

Percent of Global Abundance in Canada

Less than 5% of the global abundance of this species occurs in Canada.

Population Trend

It is estimated that the population of Kidneyshell in Canada has declined by 70% since the invasion of the Great Lakes by dreissenid mussels. This estimate is based on the number of historical records that occur in waters that now contain dreissenid mussels.

Biological Limiting Factors

Reproductive Attributes

The reproductive biology of the Kidneyshell follows the general reproductive biology of most unionid 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. Further development to the juvenile stage can not continue without a period of encystment on the host. Members of the genus Ptychobranchus have evolved a specialized method of delivering glochidia designed to increase the likelihood of encountering a suitable host. The glochidia are released in mucous encased packages termed conglutinates which have been shown to resemble fish fry complete with eye spots, or benthic invertebrates such as chironomids. These two forms represent prey items of the host species and stimulate the feeding instincts of the host resulting in an active uptake into the mouth where the conglutinates rupture, releasing glochidia in close proximity to the gills of the host. The hookless glochidia become encysted on the gills of the host and are encapsulated in a fluid filled sac where they are nourished by the host until they metamorphose and break free, settling to the substrate to begin life as free-living juveniles. Three glochidial host fishes have been identified for the Kidneyshell in Canada: blackside darter (Percina maculata); fantail darter (Etheostoma flabellare); johnny darter (E. nigrum) (McNichols and Mackie 2004). In Canada, Kidneyshells are known to be gravid between September and November and encystment has been shown to last up to 60 days resulting in the potential for encysted glochidia on the host fishes anytime between September and January (McNichols and Mackie 2004).

Dispersal

Like most native freshwater mussels, Kidneyshell 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.

3. Threats

The Round Hickorynut and the Kidneyshell, like most mussel species, are sensitive to a wide variety of stressors including exotic species, poor water quality resulting from point (industrial and residential discharge) and non-point (herbicide, pesticide and surface run-off) sources, loss of host fish species, impoundments, siltation/sedimentation, predation and urbanization. The following discussion of threats focuses on those threats which are specific to the two remaining populations of the Round Hickorynut (St. Clair delta, Sydenham River) and three remaining populations of the Kidneyshell (St. Clair delta, Sydenham River, Ausable River) although it is likely that all of the stressors listed previously have contributed to the decline of these species in Canada.

Threats to Extant Populations

St. Clair Delta Population

The introduction and spread of the exotic zebra and quagga mussels throughout the Great Lakes basin has resulted in steep declines of native mussel species (Schloesser et al. 1996). These invasive mussels are known to attach to the shells of unionids and can cause death by interfering with feeding, respiration, excretion and locomotion (Haag et al. 1993; Baker and Hornbach 1997). COSEWIC (2003b) reported that 64% of the Canadian sites where the Round Hickorynut was historically found are now infested with zebra mussels rendering much of the habitat unsuitable for unionids. The St. Clair delta population occurs in waters inhabited by zebra mussels and Round Hickorynuts were found in areas with relatively high zebra mussel infestation rates (D. McGoldrick, National Water Research Institute, Environment Canada, pers. comm., October 2003). It is not known why the mussels of the St. Clair delta have survived when other areas in Lake St. Clair have been devastated by the zebra mussel invasion (Nalepa et al. 1996) nor is it known if this population will persist (Zanatta et al. 2002). The St. Clair delta Round Hickorynut and Kidneyshell populations are very small with only 9 Round Hickorynuts and 1 Kidneyshell detected during sampling of nearly 15,000  in 2003 (Metcalfe-Smith et al. 2004)). These populations are dominated by relatively large, older individuals indicating poor reproductive success with the possibility of frequent year-class failure (COSEWIC 2003b).

Sydenham and Ausable River Populations
Water Quality

The Sydenham River flows through an area of prime agricultural land in southwestern Ontario and over 85% of the land in the watershed is in agricultural use with 60% of land in tile drainage (Staton et al. 2003). Large areas of the river have little to no riparian vegetation as only 12% of the original forest cover remains. Strayer and Fetterman (1999) identified high sediment and nutrient loads and toxic chemicals from non-point sources, especially agricultural activities, as the primary threat to riverine mussels. Agricultural lands, particularly those with little riparian vegetation and large amounts of tile drain, allow large inputs of sediments to the watercourse. In the case of tile drained land, the sediment input is often of a very fine grain which can clog the gill structures of mussels resulting in decreased feeding and respiration rates and reductions in growth efficiency. The Sydenham River has historically shown high nutrient levels with total phosphorus levels consistently exceeding provincial water quality levels over the last 30 years while chloride levels have shown recent inclines due to an increased use of road salt (Staton et al. 2003).

Agriculture is also the dominant land-use within the Ausable River basin with over 80% of the land in agricultural use and 71% of the land area in tile drainage (Nelson et al. 2003). Suspended sediment levels are high throughout the river with levels in the lower main channel consistently exceeding those required to maintain good fisheries (Nelson et al. 2003). Nutrient levels (N, P, un-ionized ammonia) regularly exceed provincial Water Quality Objectives for the protection of wildlife and Canadian Council of Ministers of Environment guidelines. Recent evidence has shown that juvenile mussels are among the most sensitive aquatic organisms to ammonia toxicity (Mummert et al. 2003; Newton 2003; Newton et al. 2003).

Dissolved oxygen (DO) levels in the East Sydenham River typically average about 10 mg/L however levels at all four Provincial Water Quality Monitoring Stations in this basin have dropped as low as 5 mg/L during the last 35 years (Jacques Whitford Environment Ltd. 2001). Over the same time period, DO levels in the Ausable River have on occasion fallen to comparable levels (2-3 mg/L) (Nelson et al. 2003). Johnson et al. (2001) have found mussel survival rates are closely related to DO levels while Tetzloff (2001) reported massive mussel die-offs in Big Darby Creek, Ohio, following a low oxygen event resulting from a chemical spill. Kidneyshells were one of the most sensitive species to these conditions with greater than 95% mortality, much of it coming rapidly after the onset of low oxygen conditions. Three years after the low O2 event many of the affected species have still not recovered to pre-event levels (pers. comm., J. Tetzloff, Darby Creek Association Inc., March 2004).

Water Quantity

Hydrologic regimes can affect mussels in a number of ways. High flow conditions can cause dislodgement and passive transport of mussels from areas of suitable habitat into areas of lesser or marginal habitat. Neither the Round Hickorynut nor the Kidneyshell show the typical shell adaptations associated with resistance to scour and shear stress associated with hydrologically flashy rivers (pustules, ridges, fluting) (Watters 1994). In contrast to the dislodgement associated with high flows, low flows can result in depressed dissolved oxygen levels, desiccation, and elevated temperatures. In a study of drought conditions in relation to mussel survival, Johnson et al. (2001) identified the need for instream flow protection as a critical issue for mussel conservation and protection in the southwestern U.S. Low flow events in the Ausable River often result in the stranding of mussels.

Host Fish

The Round Hickorynut is an obligate parasite unable to complete its early life stages without a suitable host. The host species for the Round Hickorynut has not yet been confirmed in Canada although evidence indicates the greenside darter (see Reproductive Attributes section) likely functions as a Canadian host. Clark (1977) also noticed an association between the Round Hickorynut and the eastern sand darter (Ammocrypta pellucida) suggesting a possible host relationship although this species has not been formally tested (M. McGregor, Kentucky Department of Fish and Wildlife Resources, pers. comm., January 2004). The greenside darter is considered a species of special concern in Canada where it is found in both the Sydenham River and Lake St. Clair although it is believed to be relatively abundant and stable in the Sydenham River (Dextrase et al. 2003).The eastern sand darter is listed as a threatened species in Canada but can be found in the East Sydenham River in areas where the Round Hickorynut persists. Siltation resulting from agricultural activities has been cited as one of the main reasons for the decline of the eastern sand darter (Holm and Mandrak 1996).

Three species have been identified as hosts for the Kidneyshell: blackside darter; fantail darter; johnny darter (McNichols and Mackie 2004). Recent surveys have shown that johnny darters and blackside darters are abundant throughout the Ausable (Nelson et al. 2003) and Sydenham rivers (N. Mandrak, Department of Fisheries and Oceans, Burlington, pers. comm., March 2004) while fantail darters are neither abundant nor widespread in either system. If johnny darters or blackside darters are acting as a host for wild populations in the Ausable or Sydenham rivers then host limitation should not be a primary cause of the observed declines. Only a heavy reliance on the fantail darter as the host would appear to place these species in danger of being host-limited.

Any threats that affect the host species' abundance, movements, or behaviour during the period of glochidial release must be considered as threats to these mussels as well. For example, the invasive round goby has been implicated in the following declines of native benthic fish species in the lower Great Lakes: 1) logperch (Percina caprodes) and mottled sculpin (Cottus bairdi) populations in the St. Clair River (French and Jude 2001); 2) johnny darter (Etheostoma nigrum), logperch, and trout-perch (Percopsis omiscomaycus) in Lake St. Clair (Thomas and Haas 2004); and, 3) channel darter (P. copelandi), fantail darter (E. flabellare), greenside darter (E. blenniodes), johnny darter, and logperch in the Bass Islands, western Lake Erie (Baker 2005). Index trawling data from 1987 to 2004 (unpublished data, Lake Erie Fisheries Assessment Unit MNR) indicate that similar declines have occurred in the Inner Bay of Long Point Bay and the western basin of Lake Erie. Potential causes include goby predation on eggs and juveniles, competition for food and habitat, and interference competition for nests (French and Jude 2001, Janssen and Jude 2001). The round goby poses a real threat to host fish populations and could seriously impact the future survival and recovery of Round Hickorynut and Kidneyshell populations.

Table 1: Assessment of threats to extant populations of the Round Hickorynut and Kidneyshell.
St. Clair delta and Sydenham River threats apply to Round Hickorynut and Kidneyshell populations. Ausable River threats apply only to the Kidneyshell population in the Ausable River.
ThreatRelative Impact
predominant/ contributing
Spatial/Temporal
widespread/local
chronic/ephemeral
Certainty
probable/speculative/unknown
St. Clair deltaSydenham RiverAusable RiverSt. Clair deltaSydenham RiverAusable RiverSt. Clair deltaSydenham RiverAusable River
Dreissenid musselspredominant--widespread chronic--probable--
Siltation-predominantpredominant-widespread chronicwidespread chronic-probableprobable
Water quality – nutrients & contaminantscontributingcontributingcontributingwidespread
chronic
widespread
chronic
widespread
chronic
speculativeprobableprobable
Water quantity-contributingcontributing-widespread ephemeralwidespread ephemeral-speculativespeculative
Decline of host fishcontributingcontributing-widespread
chronic
widespread
chronic
-speculativespeculative-
Urbanization-contributingcontributing-local
chronic
local
chronic
-speculativespeculative
Impoundments-contributing--local
chronic
--unknown-
Predation-contributingcontributing-local
ephemeral
local
ephemeral
-unknownunknown

Threats in Historically Occupied Habitats

Welland River

A single record exists for the Round Hickorynut in the Welland River consisting of a single shell collected in 1931 by an unidentified collector (COSEWIC 2003a). Its current status in this river is unknown. The small 880 km² watershed of this river is dominated by rural land-uses and the river is subject to many of the same disturbances seen in the larger rural watersheds of southwestern Ontario which have contributed to the decline of freshwater mussels in these systems (A. Mack, Niagara Peninsula Conservation Authority, pers. comm. February 2004). Intensive agricultural activity coupled with extensive tile drainage and reduced riparian vegetation has resulted in high sediment inputs to the river, increased turbidity, elevated nutrient and bacterial levels and an overall reduction in the quantity and quality of aquatic habitat (Central Welland River Watershed Plan).

Grand and Thames Rivers

The existence of the Round Hickorynut in the Grand River is indicated by three shells collected between 1966 and 1972 (COSEWIC 2003a). The Kidneyshell was probably more abundant in the Grand River than the Round Hickorynut as it was historically reported from 7 sites along a 50 km stretch between Caledonia and Port Maitland (COSEWIC 2003b). Recent surveys indicated no sign of live individuals of either species at 95 sites throughout the main channel and tributaries suggesting that the species may have been extirpated from the Grand River for an extended period of time. Like the Grand River population, the Thames River Round Hickorynut population is believed to have been lost as early as the turn of the 20th century (COSEWIC 2003a) with no live specimens collected since 1894. Several fresh shells of the Kidneyshell have been collected from the Thames River between London and Chatham as recently as 1997, however live specimens have never been collected (COSEWIC 2003b).

It is difficult to attribute a cause to the historic loss of populations such as those in the Grand and Thames Rivers although untreated wastewater inputs from major urban centres in these watersheds likely contributed to the declines.

Lake St. Clair, Detroit River, Lake Erie and Niagara River

The loss of the Round Hickorynut and Kidneyshell from historical habitat in these water bodies can be largely attributed to the detrimental effects of zebra mussels. Although, there is some indication that the Lake Erie population of the Round Hickorynut was in decline in the first half of the last century and may have been extirpated as early as 1950 (COSEWIC 2003a). Dreissenid mussels, however, pose the greatest limitation on recovery in these areas.

4. Habitat – Round Hickorynut

Description

The Round Hickorynut is typically found in medium-sized to large rivers (van der Schalie 1938; Strayer 1983; Parmalee and Bogan 1998), but is also known from Lake Erie and Lake St. Clair (Clarke 1981; Strayer and Jirka 1997). The preferred habitat of the Round Hickorynut is generally described as sand and gravel substrates with steady, moderate flows at depths of up to 2 m (Ortmann 1919; Gordon and Layzer 1989; Parmalee and Bogan 1998). In southeastern Michigan, however, it has mainly been found in turbid, low-gradient, hydrologically unstable rivers with clay/sand or clay/gravel substrates (van der Schalie 1938; Strayer 1983). In Lake St. Clair, O. subrotunda currently occupies shallow (<1 m) nearshore areas with firm, sandy substrates (Zanatta et al. 2002).

Currently Occupied Habitat

Geospatial Description

Habitat in need of conservation for the Kidneyshell has been geospatially located using the methods developed by McGoldrick et al (2005) (Figures 7 and 8) who recommend using the Ontario Ministry of Natural Resource's Aquatic Landscape Inventory Software (ALIS version 1) (Stanfield and Kuyvenhoven 2005) as the base unit for definition of important habitat within riverine systems. The ALIS system employs a valley classification approach to define river segments with similar habitat and continuity on the basis of hydrography, surficial geology, slope, position, upstream drainage area, climate, landcover and the presence of instream barriers. For Great Lakes populations where ALIS segments can not be employed, McGoldrick et al (2005) recommend using a 5km buffer around known species occurrences. The 5 km buffer was selected in light of the spatial extent of historic sampling within Lake St. Clair. Within all identified river segments the width of the habitat zone is defined as the area from the mid-channel point to bankfull width on both the left and right banks.

Figure 7: Currently Occupied habitat zone for the Round Hickorynut in the Sydenham River. Areas within this zone matching the functional description should be considered habitat in need of conservation.
Figure 7: Currently Occupied habitat zone for the Round Hickorynut in the Sydenham River. Areas within this zone matching the functional description should be considered habitat in need of conservation.

Functional Description

Within the area defined under Currently Occupied Habitat only areas meeting the characteristics described below are deemed to represent habitat in need of conservation:

  • permanently wetted and
  • of a stream order greater than 2 (riverine population only) and
  • having sand/gravel substrates and
  • steady to moderate flows (riverine populations only) or
  • nearshore areas with firm sand substrat. (Great Lakes populations).
Activities Likely to Impact Currently Occupied Habitat

The Currently Occupied Habitat of the Kidneyshell could be negatively affected by a variety of activities. Direct destruction could result from in-stream activities such as dredging, bridge and pipeline crossings or the construction of dams. Habitat could also be negatively affected by any land-based activities that affect water quality or quantity. Such activities would include, but are not limited to, the input of nutrients, sediment and toxic substances through improperly treated storm water, cultivation of riparian lands, unfettered access of livestock to the river, channelization and drainage works, water taking, aggregate extraction, and the release of improperly treated sewage.

Figure 8: Currently Occupied habitat zone for the Round Hickorynut in the Lake St. Clair delta. Areas within this zone matching the functional description should be considered habitat in need of conservation.
Figure 8: Currently Occupied habitat zone for the Round Hickorynut in the Lake St. Clair delta. Areas within this zone matching the functional description should be considered habitat in need of conservation.

When dealing with freshwater mussels it is necessary to consider not only the physical and chemical components of habitat but also the biological. Any activity which disrupts the connectivity between Kidneyshell populations and their host species (see section on Reproduction) may result in the destruction of habitat. Activities which may disrupt the mussel-host relationship include, but are not limited to, damming, dewatering and sport or commercial harvest. Note that activities occurring outside the Currently Occupied Habitat zone may affect the host population within the zone (e.g., downstream damming activites may prevent the movement of fish into the zone during the period of mussel reproduction (September 1 – January 1)). Any activity that impacts a host population within an area of Currently Occupied Habitat should be evaluated to ensure that the reproductive cycle is not disrupted.

Historically Occupied Habitat

Historically occupied habitat is defined as all areas where the Round Hickorynut is known to have once occurred but is no longer found. Evidence for occurrence may be through records of historically collected live individuals or shells or through recent collects of weathered shells. Historically occupied habitat includes a 40km stretch of the Sydenham River from below Alvinston downstream to Florence, the Thames River from London to Chatham and the Grand River near Dunville. Historically occupied areas in the Detroit River, Lake Erie and Lake St. Clair may function as recovery habitat if the impacts of dreissenid mussels can be mitigated.

Critical Habitat

The identification of critical habitat requires a thorough knowledge of the species needs during all life stages as well as an understanding of thedistribution, quantity, and quality of habitat across the range of the species. At present, this information is not available for the Kidneyshell although Table 2 outlines activities that would assist with obtaining the required information. The activities listed in Table 4 are not exhaustive but outline the range and scope of actions identified by the Recovery Team as necessary to identify critical habitat for the round kidneyshell. It is likely that the process of investigating the actions in Table 2 will lead to the discovery of further knowledge gaps that will have to be addressed. Until critical habitat can be defined the recovery team has identified the areas listed in the Currently Occupied Habitat section as areas in need of conservation.

Table 2: Schedule of activities to identify critical habitat
ActivityApproximate Timeframe1
Conduct mussel population surveys
2006-2008
Assess habitat conditions in occupied areas (e.g., flow, substrate, water clarity and quality)
2006-2008
Determine any life stage differences in habitat use
2007-2009
Survey and map areas of suitable but unused habitat within historical range
2008-2010
Assess genetic structure of populations
2006-2008
Determine host fish species
2006
Conduct host fish population surveys
2006-2008
Assess habitat use by host species
2006-2008
Determine areas of overlap between mussel and host habitat
2009-2010

1 timeframes are subject to change as new priorities arise or as a result of changing demands on resources or personnel

5. Habitat – Kidneyshell

Habitat Identification

The Kidneyshell prefers shallow areas with clear, swift-flowing water and substrates of firmly-packed coarse gravel and sand. In the Great Lakes it has been found on gravel shoals in Lake Erie and Lake St. Clair.

Currently Occupied Habitat

Geospatial Description

Habitat in need of conservation for the Kidneyshell has been geospatially located using the methods developed by McGoldrick et al (2005) (Figures 9 and 10) who recommend using the Ontario Ministry of Natural Resource's Aquatic Landscape Inventory Software (ALIS version 1) (Stanfield and Kuyvenhoven 2005) as the base unit for definition of important habitat within riverine systems. The ALIS system employs a valley classification approach to define river segments with similar habitat and continuity on the basis of hydrography, surficial geology, slope, position, upstream drainage area, climate, landcover and the presence of instream barriers. For Great Lakes populations where ALIS segments can not be employed, McGoldrick et al (2005) recommend using a 5km buffer around known species occurrences. The 5 km buffer was selected in light of the spatial extent of historic sampling within Lake St. Clair. Within all identified river segments the width of the habitat zone is defined as the area from the mid-channel point to bankfull width on both the left and right banks.

Figure 9: Currently occupied habitat zone of the Kidneyshell in the Sydenham and Ausable rivers. Areas within this zone matching the functional description should be considered habitat in need of conservation.
Figure 9: Currently occupied habitat zone of the Kidneyshell in the Sydenham and Ausable rivers. Areas within this zone matching the functional description should be considered habitat in need of conservation.

Functional Description

Within the area defined under Currently Occupied Habitat areas meeting the characteristics described below are deemed to represent habitat in need of conservation:

  • permanently wetted and
  • of a stream order greater than 2 (riverine population only) and
  • having firmly-packed coarse gravel and sand substrates and
  • swift-flowing waters (riverine populations only) or
  • gravel shoal. (Great Lakes populations).
Activities Likely to Impact Currently Occupied Habitat

The Currently Occupied Habitat of the Kidneyshell could be negatively affected by a variety of activities. Direct destruction could result from in-stream activities such as dredging, bridge and pipeline crossings or the construction of dams. Habitat could also be negatively affected by any land-based activities that affect water quality or quantity. Such activities would include, but are not limited to, the input of nutrients, sediment and toxic substances through improperly treated storm water, cultivation of riparian lands, unfettered access of livestock to the river, channelization and drainage works, water taking, aggregate extraction, and the release of improperly treated sewage.

When dealing with freshwater mussels it is necessary to consider not only the physical and chemical components of habitat but also the biological. Any activity which disrupts the connectivity between Kidneyshell populations and their host species (see section on Reproduction) may result in the destruction of habitat. Activities which may disrupt the mussel-host relationship include, but are not limited to, damming, dewatering and sport or commercial harvest. Note that activities occurring outside the Currently Occupied Habitat zone may affect the host population within the zone (e.g., downstream damming activities may prevent the movement of fish into the zone during the period of mussel reproduction (September 1 – January 1)). Any activity that impacts a host population within an area of Currently Occupied Habitat should be evaluated to ensure that the reproductive cycle is not disrupted.

Figure 10: Currently occupied habitat zone of the Kidneyshell in the Lake St Clair delta. Areas within this zone matching the functional description should be considered habitat in need of conservation.
Figure 10: Currently occupied habitat zone of the Kidneyshell in the Lake St Clair delta. Areas within this zone matching the functional description should be considered habitat in need of conservation.

Historically Occupied Habitat

Historically occupied habitat is defined as all areas where the Kidneyshell is known to have once occurred but is no longer found. Evidence for occurrence may be through records of historically collected live individuals or shells or through recent collects of weathered shells. Historically Occupied Habitat for the Kidneyshell includes a 50 km of the Lower Grand River from Caledonia to Port Maitland, a small portion of the Welland River, and a stretch of the Thames River between London and Chatham. Historically occupied areas in the Detroit River, Lake Erie and Niagara River will only function as potential recovery habitat if the impacts of dreissenid mussels can be eliminated.

Critical Habitat

The identification of critical habitat requires a thorough knowledge of the species needs during all life stages as well as an understanding of the distribution, quantity, and quality of habitat across the range of the species. At present, this information is not available for the Kidneyshell although Table 3 outlines activities that would assist with obtaining the required information. The activities listed in Table 4 are not exhaustive but outline the range and scope of actions identified by the Recovery Team as necessary to identify critical habitat for the round kidneyshell. It is likely that the process of investigating the actions in Table 3 will lead to the discovery of further knowledge gaps that will have to be addressed. Until critical habitat can be defined the recovery team has identified the areas listed in the Currently Occupied Habitat section as areas in need of conservation.

Table 3: Schedule of activities to identify critical habitat
ActivityApproximate Timeframe1
Conduct mussel population surveys
2006-2008
Assess habitat conditions in occupied areas (e.g., flow, substrate, water clarity and quality)
2006-2008
Determine any life stage differences in habitat use
2007-2009
Survey and map areas of suitable but unused habitat within historical range
2008-2010
Assess genetic structure of populations
2006-2008
Determine host fish species
2006
Conduct host fish population surveys
2006-2008
Assess habitat use by host species
2006-2008
Determine areas of overlap between mussel and host habitat
2009-2010

1 timeframes are subject to change as new priorities arise or as a result of changing demands on resources or personnel

6. Habitat Trend

Habitats for the Round Hickorynut, Kidneyshell and other unionids in Lake Erie and Lake St. Clair have been largely destroyed by dreissenid mussels. Native mussel communities were virtually extirpated from the offshore waters of western Lake Erie by 1990 (Schloesser and Nalepa 1994) and the offshore waters of Lake St. Clair by 1994 (Nalepa et al. 1996). The mussel communities of Lake Erie were already in decline, probably due to a general decline in water quality over the past 40 years (Nalepa et al. 1991), but Lake St. Clair still supported an abundant and diverse mussel assemblage as recently as 1986 (Nalepa and Gauvin 1988). Unionids continue to survive in some nearshore areas with very shallow water, a high degree of connectivity to the lake (which ensures access to host fishes), and harsh conditions for dreissenid mussels (high water temperatures and considerable wave action in summer; ice scour in winter). However, such "refugia" are rare, and most of the unionid habitat in the Great Lakes has been permanently lost (COSEWIC 2003a).

The Round Hickorynut and Kidneyshell have apparently been lost from the Thames and Grand rivers, and the Round Hickorynut has declined significantly in the Sydenham River. Agriculture is believed to be the main cause of the destruction of mussel habitat across North America (Strayer and Fetterman 1999) and southwestern Ontario is no exception. Since agriculture accounts for 75-85% of land use in the Grand, Thames and Sydenham River basins, it is likely that agricultural impacts (e.g., runoff of sediment, nutrients and pesticides, increased water temperatures due to loss of riparian vegetation, destruction of habitat by tractor crossings and cattle) are primarily responsible for the loss of mussel habitat in these rivers (COSEWIC 2003a).

7. Habitat Protection

The federal Species at Risk Act (SARA) was proclaimed in June of 2003. Under SARA there are general prohibitions against killing, harming, taking, possessing, capturing, and collecting the Round Hickorynut or Kidneyshell and against damaging or destroying their residences, as well as prohibitions on the destruction of Critical Habitat. The Federal Fisheries Act represents another significant piece of legislation protecting freshwater mussels and their habitat in Canada since fish are broadly defined under the Act to include shellfish. The collection of live mussels is considered fishing and would fall under the Ontario Fishery Regulations that are made under the Fisheries Act. The protection of other fish and fish habitat under the Fisheries Act may indirectly protect the habitat of the Round Hickorynut or Kidneyshell and other species of freshwater mussels. The Provincial Policy Statement under Section 3 of the Planning Act provides for protection from development and site alteration in the significant habitats of threatened and endangered species. Other mechanisms for protecting mussels and their habitat in Ontario include the Ontario Lakes and Rivers Improvement Act, which prohibits the impoundment or diversion of a watercourse if it would lead to siltation; and the voluntary Land Stewardship II program of the Ontario Ministry of Agriculture, Food, and Rural Affairs, which is designed to reduce erosion on agricultural lands. Stream-side development in Ontario is managed through flood plain regulations enforced by local Conservation Authorities. The majority of land in the Sydenham and Ausable rivers where these mussels are found is privately owned while the land in the St. Clair delta is controlled by the Walpole Island First Nation.

8. Ecological Role

Freshwater mussels play an integral role in the functioning of aquatic ecosystems. Vaughn and Hakenkamp (2001) have summarized much of the literature relating to the role of unionids and identified numerous water column (size-selective filter-feeding; species-specific phytoplankton selection; nutrient cycling; control of phospohorus abundance) and sediment processes (deposit feeding decreasing sediment organic matter. biodeposition of feces and pseudofeces; epizoic invertebrates and epiphytic algae colonize shells; benthic invertebrate densities positively correlated with mussel density) mediated by the presence of mussel beds. Welker and Walz (1998) have demonstrated that freshwater mussels are capable of limiting plankton in European rivers while Neves and Odom (1989) reported that mussels also play a role in the transfer of energy to the terrestrial environment through predation by muskrats and raccoons.

9. Importance to People

Although these species have no apparent economic significance, freshwater mussels are sensitive to environmental pollution and a diverse mussel community indicates a healthy ecosystem. Besides decreased biodiversity in Canada, the loss of the Round Hickorynut or Kidneyshell may indicate further environmental degradation of southwestern Ontario watercourses which would adversely affect those people who depend on surface water for drinking, recreation or watering livestock.

10. Knowledge Gaps

  • What is the Canadian host for the Round Hickorynut?
    Although the host for the Round Hickorynut has been identified in the United States as the greenside darter, host specificity has been reported at the watershed scale for some species and this identification should be verified for Canadian populations if possible.

  • What are the habitat requirements of the Round Hickorynut and Kidneyshell?
    Habitat use must be quantified for all life-stages with particular attention to the glochidial, encysted and juvenile stages when mortality is high..

  • Are the Round Hickorynut and Kidneyshell host-limited?
    Host fish distributions for both mussel species need to be mapped in high detail. Host fish may be functionally unavailable to mussels if their distributions do not overlap at times when female mussels are releasing mature glochidia..

  • Are there life-stage specific threats?
    The relative importance of each identified threat to each distinct life-stage (glochidium, larva, adult) must be identified..

  • Can the St. Clair refuge sites be maintained?
    It must be determined if these sites represent permanent refugia or whether the mussels at these sites will eventually succumb to the harmful effects of dreissenid mussels. If these sites can not be naturally maintained then the feasibility of actively managing these sites to reduce the effects of dreissenid mussels must be investigated..

  • Can these species be relocated from other jurisdictions or artificially propagated for reintroduction?
    Conservation genetics need to be assessed as they relate to relocations/reintroductions and the technical feasibility of artificial propagation should be examined.

11. Biological and Technical Feasibility of Recovery

Recovery of the Round Hickorynut and Kidneyshell is believed to be both biologically and technically feasible as reproducing populations still exist as potential sources to support recovery, suitable habitat can be made available through recovery actions, threats can be mitigated and proposed recovery techniques are anticipated to be effective. Although recovery at the species level is believed to be feasible the effort required to achieve recovery will not be uniform across all populations.

  • Mussels are slow growing and sedentary animals dependant upon their host fishes for the survival and dispersal of their young. The slow rate of population growth of freshwater mussels makes the natural recovery of decimated populations extremely difficult.
  • The habitat in the Sydenham and Ausable rivers could be improved significantly with proper stewardship of both agricultural and urban lands in the watershed.
  • Reductions in soil erosion and turbidity in all the watersheds can be achieved but would be challenging due to the number and intensity of the impacts.
  • Complete removal of the impacts of dreissenid mussels to the Lake St. Clair populations is not possible at this time however it may be possible to establish managed refuge sites to reduce the impacts of dreissenid mussels on Round Hickorynuts and Kidneyshells.

A high level of effort will be required to recover the Sydenham and Lake St. Clair populations of the Round Hickorynut. There is little evidence of natural reproduction within these populations and recovery may require captive breeding and/or relocations from U.S. populations.

A low to moderate level of effort will be required to recover the Sydenham and Ausable river Kidneyshell populations. These populations are believed to be threatened by general habitat loss resulting from characteristic land-use practices within the basin. A general suite of ecosystem recovery actions such as those proposed by Dextrase et al. (2003) will assist with the recovery of this population.

Recovery of the Lake St. Clair populations of both species will require a higher degree of effort. Active management of selected refuge sites including the regular cleaning of dreissenid mussel infested individuals will be required to maintain and recover this population. Long term population augmentation and/or translocations may also be required to return the Round Hickorynut and Kidneyshell to healthy self-sustaining levels in Canada.