Mapleleaf mussel (Quadrula quadrula) COSEWIC assessment and status report: chapter 7

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Population Sizes and Trends

Ontario

Search effort

Historical surveys

Approximately 80% of the information on the historical distribution of Quadrula quadrula in Ontario is based on either museum specimens or presence-absence data. There is little if any information on sampling method, search effort, numbers of sites visited where the species did not occur, or even whether the animals were dead or alive when collected. Data on relative abundance (Catch-Per-Unit-Effort or CPUE) are available from timed-search surveys of 10 sites on the Sydenham River in 1985 (Mackie and Topping 1988) and 16 sites on the same river in 1991 (Clarke 1992). Two of the sites surveyed by Mackie in 1985 were re-surveyed 12-13 years later by Metcalfe-Smith et al. (1998b, 1999), so these data can be compared. Three of the sites surveyed by Clarke in 1991 were also re-surveyed in 1997-98, but Q. quadrula was never found at any of these sites. Kidd (1973) surveyed 68 sites on the Grand River in 1970-72 and 14 of these sites were re-surveyed 25 years later using a similar sampling effort (Metcalfe-Smith et al. 2000a). Nine sites were in the upper and middle reaches of the river, which is outside the species’ distribution in the system, but 5 sites were in the lower reaches and can be compared.

Recent surveys

Surveys conducted between 1995 and 2004 within the range of Quadrula quadrula in Ontario have been either semi-quantitative (timed-searches) or quantitative (quadrat surveys). The same sampling methods and efforts were used throughout and are described below. The only exception was the 1995 survey on the Grand River, which used a lower sampling effort than other surveys (see Metcalfe-Smith et al. 2000a).

Timed-search surveys: In rivers, surveys were conducted using an intensive timed-search technique developed by Janice Metcalfe-Smith and her team for detecting rare species of mussels. The technique is described in its entirety in Metcalfe-Smith et al. (2000b). Briefly, the riverbed is visually searched by a team of 3 or more persons using waders, polarized sunglasses, and underwater viewers for a total of 4.5 person-hours (p-h) of sampling effort. Where visibility is poor, searching is done by feel. The length of reach searched varies depending on river width, but is generally 100-300 m. Live mussels are held in the water in mesh diver’s bags until the end of the search period when they are identified to species, counted, measured (shell length), sexed (if sexually dimorphic) and returned to the riverbed. Over the past 10 years, such surveys have been conducted in the Grand, Thames, Sydenham, Ausable, Maitland, Saugeen and Moira Rivers and several smaller tributaries to Lake Ontario and Lake Erie by several different researchers.

In Lake St. Clair, searches at waters depths greater than 2 m were conducted by two SCUBA divers for a total effort of 0.5 p-h whereas searches at depths less than 2 m were conducted by three people using mask and snorkel for a total of 0.75 p-h (Zanatta et al. 2002). At sites where live mussels were found (all were shallow), snorkel searches were extended to a total of 1.5 p-h.

Quantitative surveys: Surveys in rivers employed an intensive quantitative sampling technique that would allow the generation of precise estimates of demographic variables such as density, size class frequencies and recruitment levels. The monitoring protocol was developed in consultation with Dr. David R. Smith, a biostatistician with the U.S. Geological Survey who advises the U.S. Army Corps of Engineers on methods for assessing the impacts of development projects on federally endangered mussels in the United States. Dr. Smith and Dr. David L. Strayer, another American mussel expert, were recently commissioned by the Guidelines and Techniques Committee of the Freshwater Mollusk Conservation Society to prepare a guide to sampling freshwater mussel populations. This guide (Strayer and Smith 2003) includes a description of the protocol, which is summarized below:

Sampling employed a 2-person search team and a data recorder and required approximately 2 days of work per site. At each site, roughly 400 m² of the most productive portion of the reach (usually a riffle) was selected for sampling. Quantitative sampling was conducted using 1 m² quadrats and a systematic sampling design with three random starts. The area to be sampled was divided into blocks of equal size (5 m long × 3 m wide) and each block was further divided into 15 – 1 m² quadrats. The same three randomly chosen quadrats were sampled in each block; thus, 20% of the 400 m² area was sampled at each site. Each quadrat was searched by 2 people until all live mussels had been recovered (~ 8 person-minutes). All embedded stones (except large boulders) were removed and the substrate was excavated to a depth of 10-15 cm in order to obtain juveniles (young mussels are known to burrow deeply in the substrate for the first three years of life). All live mussels found in each quadrat were identified, counted, measured, sexed where possible and returned to the riverbed. Several habitat variables (e.g., depth, current velocity, substrate composition) were also measured and recorded. To date, quantitative surveys have only been conducted on the Sydenham and Thames Rivers.

Quantitative surveys were also conducted in the delta area of Lake St. Clair. At each site, sampling was performed by several (usually three) 2-person teams, with each team consisting of a snorkeler and a helper to carry the gear and mussels. Each snorkeler swam until a mussel was seen, then surveyed a 65 m² circular area around the mussel and collected any other live mussels found. Each team surveyed 10 such circle plots. All live mussels were identified, counted, measured, sexed and returned to the lake bottom. Methods are described in detail in Metcalfe-Smith et al. (2004). Such surveys were conducted in 2001 and 2003 and to a limited extent in 2004.

Abundance

Quadrula quadrula no longer occurs in the Great Lakes and connecting channels, so there are no abundance data to discuss for these waters (see section on Fluctuations and Trends). The species presently occurs in the Grand River (Lake Erie drainage), Thames and Sydenham rivers (Lake St. Clair drainage) and Ausable River (lower Lake Huron drainage) of southwestern Ontario. Timed-search surveys were conducted at 113 sites on these rivers between 1997 and 2004 using 4.5 p-h sampling effort/site. Results of such semi-quantitative surveys can be used to compare the relative strengths of Q. quadrula populations among rivers (Table 4). Quadrula quadrula is a minor component of the mussel fauna in all four rivers. It was found at the greatest proportion of sites in the Sydenham River but made up the largest proportion of the mussel community by abundance in the Grand River. The population in the Ausable River is extremely small, with only 18 live specimens found. Based on CPUE, population densities in the Grand and Sydenham Rivers are greater than those in the Thames and Ausable Rivers. However, these numbers may be somewhat misleading. Quadrula quadrula mainly occurs in the lower reaches of medium-sized to large rivers and a large proportion of the sites surveyed in both the Grand and Thames Rivers were in the headwaters or tributaries. If CPUE is compared using only those data from sites in the occupied reaches of each river, population density is greatest in the Grand River (CPUE = 6.9 specimens/p-h), followed by the Thames (2.9), Sydenham (2.0) and Ausable (1.0). However, DFO personnel completed timed-search (4.5 p-h) surveys at each of 10 sites on the Lower Thames River in 2005 and found 3134 living specimens and 20 species, of which 422 were Q. quadrula (Table 4). The species was the 2nd to 3rd most abundant at virtually all sites (T.J. Morris, Department of Fisheries and Oceans, Burlington, ON, unpublished data, 2006). The CPUE for this species in the survey was 9.5 specimens/p-h which is over three times the CPUE reported in previous surveys (2.9 specimens/p-h). It appears that the Thames River may have the largest population of Q. quadrula in Southwestern Ontario.

Catch-per-unit effort data obtained from timed-search surveys provide information on relative population density. True density estimates are only available at present for the Sydenham River (Note: quantitative surveys were also conducted at 5 sites on the Thames River in 2004, but all sites were in the headwaters and no Quadrula quadrula were found). Twelve sites on the East Sydenham River and 3 sites on the north branch of the river (known as Bear Creek) were quantitatively sampled between 1999 and 2003. Quadrula quadrula was found at 9 sites on the East Sydenham at an average density of 0.218 individuals/m². As the species was found at every site surveyed by timed-searches, quadrat sampling or both techniques within the occupied reach of the East Sydenham, it is reasonable to assume that the population is continuous. Based on an average density of 0.218 individuals/m² and an AO of 1.2 km², population size is estimated to be 261,600 animals. Quadrula quadrula was found at one of the 3 sites sampled on Bear Creek at a density of 0.16 individuals/m². It was also found at the next-closest site downstream that was surveyed during timed-searches in 1998. Based on an average density of 0.16 individuals/m² and an AO of 0.16 km² and assuming the population is continuous, population size is estimated to be 25,600 animals. It is likely that the Grand and Thames River populations of Q. quadrula are an order of magnitude larger and the Ausable River population an order of magnitude smaller than the population in the Sydenham River. This would result in an overall estimate of approximately 5.5 million individuals, including the 2005 data collected by DFO personnel in the lower Thames River.

Shell length was measured for every live mussel collected during the above-described surveys. Size frequency distributions for live Quadrula quadrula collected during recent timed-search surveys on the Grand, Thames and Ausable Rivers are presented in Figure 9. Size frequency distributions for live Q. quadrula collected during both timed-search and quadrat surveys on the Sydenham River are shown in Figure 10. As expected, more small specimens were collected during quadrat surveys with excavation of the substrate than during timed-search surveys; however, the data from both types of survey show that the population is healthy and reproducing. Specimens captured in the Grand River measured 16 to 125 mm in shell length with good representation in many different size classes. Such a distribution is indicative of a healthy, reproducing population. Based on specimens collected in 1997-98 and 2004, the population in the Thames River was dominated by larger animals with < 10% of individuals measuring less than 80 mm – a pattern that suggests recruitment may be declining or no longer occurring. However, DFO surveys of 10 sites in the lower Thames indicate that nearly 33% of individuals are less than 80 mm and the size distribution is statistically indistinguishable from normal (Figure 11) indicating active reproduction and recruitment (T.J. Morris, Department of Fisheries and Oceans, Burlington, ON, pers. comm, 2006). Nothing can be said about the population in the Ausable River from only 18 specimens. The population is so sparse that additional sampling effort would be needed to determine if there has been recent recruitment.

Figure 9. Size frequency distributions for live Quadrula quadrula collected from the Grand, Thames and AusableRivers, Ontario, from 1997 to 2004.

Figure 10. Size frequency distributions for live Quadrula quadrula collected during timed-search and quadrat surveys in the Sydenham River, Ontario, from 1997 to 2003.

Figure 11.  Size frequency distributions for live Quadrula quadrula collected during timed-search surveys in the lower Thames River by DFO in 2005 (T.J. Morris, Department of Fisheries and Oceans, Burlington, ON, pers. comm., 2006).

Fluctuations and trends

Quadrula quadrula appears to be extirpated from Lake Erie, Lake St. Clair and the Detroit and Niagara Rivers due to impacts of the zebra and quagga mussels; however, it was always extremely rare in these waters. For example, there are some scattered records from Canadian waters of Lake Erie, but only for shells. These records include 3 from Rondeau Bay (1894, 1961 and one with no date), 4 from Pelee Island (1962, 1978, 1992, and 2004) and one from Port Maitland at the mouth of the Grand River in 1936. Quadrula quadrula was found at only one of 29 sites surveyed in the offshore waters of Lake St. Clair in 1986 prior to the zebra mussel invasion and represented 0.7% of the 281 mussels collected from all sites (Nalepa et al. 1996). Similarly, only 1 of 1279 live mussels (0.08%) collected from 13 sites throughout the Detroit River in 1982-83 were this species (Schloesser et al. 1998). Finally, Zanatta et al.(2002) collected 2356 live mussels from 95 sites in the nearshore waters of Lake St. Clair between 1999 and 2001, and only one mussel (0.04%) was a Quadrula quadrula. Nevertheless, even at low population densities, because of their enormous size these waterbodies must have once supported a substantial proportion of the Ontario population of this species.

Catch-per-unit-effort reported for Quadrula quadrula in the Sydenham River was 1.4/p-h over 10 sites in 1985 (Mackie and Topping 1988), 0.12/p-h over 6 sites in 1991 (Clarke 1992) and 1.1/p-h over 18 sites in 1997-98 and 2003 (Metcalfe-Smith et al. 1998b, 1999, unpublished data). Two sites were surveyed in both 1985 and 1998; CPUE for a site on the East Sydenham was 8.0/p-h in 1985 and 1.1/p-h in 1998, and CPUE for a site on Bear Creek was 5.0/p-h in 1985 and 1.3/p-h in 1998. These data suggest that Q. quadrula may be declining in abundance in the system but this is inconsistent with evidence showing that the species is encountered more frequently now than in the past (see section on Distribution). Kidd (1973) collected 0, 0, 0, 1 and 9 Q. quadrula from 5 sites on the lower Grand River in 1971-72 whereas Metcalfe-Smith et al. (2000a) collected 0, 0, 1, 57 and 27 specimens from the same sites 25 years later. Kidd (1973) found that the number of mussel species living in the river had declined dramatically from historical counts – only 6 of 25 species previously reported from the lower reaches were still present in the 1970s. This decline was attributed to siltation, the creation of dams and reservoirs and especially sewage pollution. Quadrula quadrula was one of the species that had survived. Populations of most mussel species, including Q. quadrula, have since rebounded due to significant improvements in water quality. There are no data available for determining if there have been changes in population size over time for Q. quadrula in the Ausable or Thames Rivers, although the recent data on 10 sites in the lower Thames suggests a healthy population (Fig. 11).

Rescue effect

All Ontario populations of Quadrula quadrula are isolated from one another and from other populations in Manitoba and the United States; thus, there is no chance of a healthy population of the species returning to Ontario if the population should become extirpated in Ontario. Populations in tributaries to the lower Great Lakes on both sides of the Canada/U.S. border may once have been connected by populations in Lake Erie and Lake St. Clair, but native mussels have been virtually extirpated from the lakes due to impacts of the zebra and quagga mussels and this connection has been broken. Although the catfish hosts are vagile, there is no robust population in the U.S. part of the Lake Erie drainage from which a rescue effect can occur. The continued decline of these populations is testament to the absence of a rescue effect.

Manitoba

Search effort

Historical surveys

All of the historical information for the distribution of Quadrula quadrula in Manitoba is either museum specimens or in the form of presence-absence data. Data on sampling methods and search efforts are unavailable. Sites where Q. quadrula did not occur can be determined by comparison with sites from which other species were recovered. However, there are no data on sites that were examined from which no mussel species were recovered.

Recent surveys

There are 7 recent surveys that report on the distribution of freshwater mussels in Manitoba. The goals of these surveys differed, as did the collecting methods and efforts. This makes comparisons difficult. In 1992, under the direction of Dr. Terry Dick from the University of Manitoba, Carney and colleagues (unpublished data) surveyed 4 sites on the Assiniboine River and 1 site on the Roseau River to provide a preliminary determination of what mussel species were present. Quadrula quadrula was recovered from 3 sites on the Assiniboine and from the single site on the Roseau River. This undertaking is best considered as qualitative because of different times spent searching involving different numbers of people (range from 1-5). Search in all cases was by feel. The effort expended varied from a low of 2 person hours to a high of 10 person hours (Table 5).

Scaife and Janusz (1992) investigated the viability of a commercial shell harvest from the lower Assiniboine River. They reported the results of a survey over 21 km using randomly placed 1 m² quadrats and SCUBA. Scaife and Janusz (1992) reported 62 Quadrula quadrula from 24 of 120 quadrats and an average density of 0.52/m².

Watson et al. (1998) undertook a study to determine the distribution and abundance of freshwater mussels in the lower Assiniboine River and 15 of its tributaries. Sampling sites on the Assiniboine between Portage la Prairie and Winnipeg were selected following a stratified sampling design (Watson et al.1998). Eighteen transects across the river were sampled using a mini bullrake. Collecting involved raking the bullrake across the substrate 5 times at each of 5 equidistant points across the river. Tributaries were sampled by sight, by feel, or by using the bullrake, depending on water clarity and depth. Thirty person-minutes were spent searching at each site. They (Watson et al. 1998) recovered a total of 6 live Quadrula quadrula from 5 of the 17 sites surveyed on the Assiniboine River, with empty valves recorded at one additional site. There was no evidence of Q. quadrula from any of the 167 sites surveyed on tributaries of the Assiniboine.

Pip (2000) in 1998 undertook a very large survey of freshwater molluscs in Manitoba for comparison to the results from previous surveys. Although the focus of this survey was directed to gastropods there were results relevant to mussels. Of particular interest is the fact that there was a decline from 4 to 2 in the number of sites from which Quadrula quadrula were recorded. This decline occurred in the 20 year interval from the previous survey. Unfortunately no collecting methodology, site information or abundance data were reported (Pip 2000).

Carney (2003a, 2004a) collected mussels from sites along the length of 10 different rivers in Manitoba. The purpose was to collect tissue for DNA analyses, determine the reproductive status and demographics and investigate the parasites of the mussels. Permits restricted the number to no more than 20 individuals of any one species from any single site, excepting one reference site on the lower Assiniboine. Once 20 individuals of a species had been collected that species was no longer collected. As a result, collecting effort on common species would stop and the focus would be on the less common species. Nonetheless, time spent searching was noted so effort in terms of person hours could be determined. At no site was the limit for Quadrula quadrula reached and in fact effort was focused on this species due to its rarity and absence of evidence for successful production of glochidia.

Carney (2004b) reported the results of a quantitative survey of mussels in the Assiniboine River through Spruce Woods Provincial Park. A total of 620 1 m² quadrats at 49 transects were searched with no Quadrulaquadrula being recovered. The average density for all species in this study was estimated to be 0.08/m².

Quadrula quadrula from the Bloodvein River, which drains into the east side of Lake Winnipeg, has recently been reported (Staton, pers. comm.). A single live specimen was opportunistically collected during a recreational canoe trip so nothing more can be said regarding the occurrence of this species in this particular river, other than there is evidence that the species is present. There have been no historical surveys of mussels in this, or other rivers from this side of Lake Winnipeg. More surveys need to be done on the rivers flowing into the east side of Lake Winnipeg to evaluate the possibility of mussel populations being present.

Abundance

Estimating the density of Quadrula quadrula in Manitoba is possible only for the lower Assiniboine River using the results reported by Scaife and Janusz (1992). As described previously Scaife and Janusz (1992) recovered 62 Q. quadrula from 24 of the 120 quadrats using SCUBA. This would result in an average density of 0.52 Q. quadrula/m². This should be considered an upper bound inasmuch as Carney (2004b) reported an average density of 0.08/m² for all mussel species from a larger survey on a different shallower stretch of the Assiniboine River sampled by wading from shore to shore.

If we accept 0.52/m² as an approximate upper estimate of the density of Quadrula quadrula then we can estimate the population size within this river. The data indicate that Q. quadrula is limited in the Assiniboine River to locations from the Portage Diversion to the confluence with the Red River in Winnipeg. The area of occupancy (AO) for this stretch of the Assiniboine River is 7.5 km² (Table 3). At a density of 0.52 per m², this provides an estimate of a total population in this river of 3,900,000 individuals. It needs to be noted that this should be considered an extreme upper bound because long stretches of the Assiniboine have a substrate of drifting soft sand unsuited as mussel habitat. This is reflected in the much lower density values for all species reported by Carney (2004b). Furthermore, Watson et al. (1998) recovered Q. quadrula from 27% of sites along the Assiniboine River. This many samples along the Assiniboine without Q. quadrula clearly indicate that this species does not occur along the entire length of this river. If we use this value (27%) to calculate the proportion of the river suitable for Q. quadrula we arrive at a population estimate of 1,050,000 individuals. Thus we calculate the Q. quadrula population in the Assiniboine River to lie between 1 and 4 million individuals. These widely divergent numbers only serve to highlight the pressing need for more data on mussels from this, and the other Manitoba watersheds.

There are no data amenable to estimating Quadrula quadrula populations in the Red or Roseau rivers. Live specimens have not been recovered from the Red River since the investigations reported by Clarke (1973). The last live specimens from the Roseau was 1 individual collected in 1992 (Carney, unpublished data). Six other individuals were recorded by Manitoba Fisheries staff in 1991 from the lower Roseau (Erickson, pers. comm.). Based on this information it is not even known if there are viable populations in either of these rivers. It seems probable they exist in the Red River simply based on the size of the river; there is no basis for this likelihood in the Roseau River.

The single specimen collected from the Bloodvein by Staton (pers. comm.) does not permit an evaluation of abundance for that river.

Neither Watson et al. (1998) nor Scaife and Janusz (1992) reported size values for the mussels they collected. All individuals collected by Carney (2003a) were measured and aged using thin sections. Only lengths will be presented here in order to maintain consistency with the data presented for Ontario. Size frequency distributions are shown for mussels collected from the Assiniboine River reported in Carney (2004a) (Figure 12). Specimens ranged in size from 53 mm to 123 mm (mean = 101 mm). There was an absence of small individuals, which seems to be the common situation for the Manitoba populations (Carney, personal observation). The absence of smaller individuals, even in the range of 50-100 mm is indicative of little or no recruitment. It is worth noting that Carney (2003a, unpublished data) has only ever recovered 2 female Quadrula quadrulagravid with glochidia. This apparent lack of reproduction is consistent with little or no recruitment.

Figure 12. Size frequency distributions for Quadrula quadrula collected from the Assiniboine River (Carney, 2003).

Fluctuations and trends

Clarke (1973) indicated that Quadrula quadrula was relatively common to abundant (Table 2, page 12) on the one hand, but in the text indicated it was “…ordinarily uncommon…” (page 33). Where Clarke (1973) does provide collecting data the numbers collected within Manitoba are never very high. Current information is consistent with Q. quadrula being uncommon. Watson et al. (1998) surveyed the greatest number of sites in the lower Assiniboine River (below the Portage Diversion) and recorded the presence of Q. quadrula at 27% of the sites examined, recovering just 6 individuals over 157 km of river with an estimated CPUE of 0.66 (Table 5). Comparisons of CPUE indicate population densities are quite variable, even within rivers, from a low of 0 in the Red and Roseau Rivers to a high of 1.5 in the Assiniboine (Table 5). In 2003 Watkins (unpublished data) surveyed 6 sites in the Assiniboine within Winnipeg for 19.5 person-hours with a CPUE of 1.54 (range 0-9). In 2004 Carney and Watkins (unpublished data) resurveyed one of these sites (which had a CPUE = 9) for 3 person-hours and recorded a CPUE of 0.37, more than an order of magnitude below the value of the previous year. The available data indicate Q. quadrulaabundance is the highest in the Assiniboine River within and near the western perimeter of Winnipeg and then decreases proceeding upstream to the Portage Diversion and downstream toward the confluence with the Red River. Just a single individual has been documented from the almost 900 km of the Assiniboine upstream of the Portage Diversion (Carney, 2003).

The distribution of Quadrula quadrula has undoubtedly become smaller. Historical records indicate a distribution that includes the Red River and many tributaries, the length of the Assiniboine River to Lake of the Prairies and many sites in Lake Winnipeg (Figure 7). In the time period from 1992-2004 Q. quadrula has only been recorded from about ½ the length of the Assiniboine River, with the Portage Diversion representing a line of demarcation. No live specimens have recently been recovered from the Red River or from Lake Winnipeg (Figure 8). With the exception of a single individual from the Roseau River, no evidence of Q. quadrula has been observed in the other tributaries of the Red River from which it had been previously recorded.

Quadrula quadrula is likely declining in abundance within Manitoba. Clarke (1973) reported Q. quadrula from the Roseau River. Since then 6 individuals have been recorded in 1991 (Erickson, pers. comm.) and one individual in 1992 (Carney unpublished data) with no specimens being encountered in recent, more extensive, surveys of this river (Carney 2004a). No live Q. quadrula have been recently observed in the Red River (Carney 2004a, Carney and Watkins unpublished data). Clarke (1973) reported collecting 25 Q. quadrula from the Red River at St. Jean Baptiste. In 2003, Carney (2004a) during exceptionally low water was able to sample the entire width of the river at the same site and found no living specimens, but observed many empty valves along the shore. In 2004, Carney and Watkins (unpublished data) returned to this, and other sites along the Red from which Clarke (1973) had collected Q. quadrula,and using the same sampling methodology as Clarke (1973), found no living specimens of this species and just a few, highly weathered empty valves. This strongly suggests there has been a decline in abundance of Q. quadrula within the Red River in Manitoba.

Rescue effect

The Red River drainage is part of the Hudson Bay drainage with no connection to the adjacent Mississippi River drainage. Thus there could be no natural rescue of the populations in the Red River drainage from populations in the Mississippi/Missouri drainages to the east and south, respectively. Although Manitoba populations appear to occur as widely separated assemblages of individuals, there are few barriers limiting the movement of potential fish hosts, and as such, Quadrula quadrula can reasonably be considered to be a single, diffuse population. The Portage Diversion on the Assiniboine River, locks on the Red River at Lockport and lowhead dams on the Roseau represent the only barriers to fish movement within the extent of occurrence in Manitoba. The Portage Diversion is an impassable barrier for upstream movement of fish and represents a complete barrier for the upstream dispersal of glochidia-infested hosts. This precludes any natural establishment of Q. quadrula upstream of this barrier in the Assiniboine River.

The status of this species in the North Dakota and Minnesota portions of the Red River drainage are not well known. There is no recent information from North Dakota (S. Dyke pers. comm.). Investigations by Carney (2003b) did not encounter this species from sites in North Dakota reported by Cvancara (1970) to hold Quadrula quadrula. Limited recent investigations in the upper Red River undertaken by Minnesota Department of Natural Resources staff recovered just 3 Q. quadrula (M. Davis pers. comm.). A survey by Hart (1995) of the Otter Tail River, a tributary of the Red River in Minnesota, recovered just 10 Q. quadrula from a total of 4,851 individual mussels. A project to translocate mussels from 2 bridge construction sites on the Otter Tail River (Ceas 2001) reported no Q. quadrula. This would essentially be a census of the mussels from these 2 sites. These reports suggest that Q. quadrula is an uncommon component of the mussel fauna of the Red River drainage in Manitoba, North Dakota and Minnesota. The known mobility of channel catfish potential hosts (Stewart and Watkinson 2004) within the Red River suggests a limited capacity for a rescue effect from populations within the Red River system outside of Manitoba. However, the current evidence indicates that there are few populations in North Dakota and Minnesota to act as a source for rescue. There is no possibility of rescue from the Mississippi/Missouri drainage system.