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The Wavyrayed Lampmussel is subject to a broad array of threats across its range. The eight categories identified in Table 2 represent the most likely threats to Canadian populations of the Wavyrayed Lampmussel.
|Siltation/Suspended solids||predominant||widespread / chronic||probable|
|Exotics||predominant||local / chronic||probable|
|Impoundments||contributing||local / chronic||probable|
|Water Quality – contaminants & nutrients||contributing||widespread / chronic||probable|
|Disruption of host fish relationship||contributing||local / chronic||speculative|
|Predation||contributing||local / ephemeral||speculative|
|Urbanization||contributing||local / chronic||speculative|
|Recreational activity||contributing||local / ephemeral||unknown|
Siltation: High silt inputs can act to suffocate mussels by clogging gill structures and may also disrupt reproductive functions by decreasing the likelihood of encountering a suitable host fish (a visual predator). Susceptibility to siltation varies from species to species and the Wavyrayed Lampmussel has been shown to be mildly tolerant of high silt conditions during periods of low flow (Dennis 1984). However, recent studies in southern Ontario show that the Wavyrayed Lampmussel is associated with areas of low silt loads. Mean water clarity is higher in areas where Wavyrayed Lampmussels are found than in areas where they are not found and catch-per-unit-effort is positively correlated with water clarity (Metcalfe-Smith and McGoldrick 2003).
Exotics: Zebra mussels (Dreissena polymorpha) have decimated populations of freshwater mussels in the Lower Great Lakes by virtually eliminating historical habitats in Lake St. Clair (Nalepa et al. 1996) and western Lake Erie (Schloesser and Nalepa 1994). Although the Wavyrayed Lampmussel is primarily a riverine species, and therefore at lower risk to zebra mussel infestation, the presence of impoundments may increase the risk (see section on impoundments below). Zebra mussels pose a much greater risk for the St. Clair delta population: the last known lake population in Canada.
Other exotic species may indirectly affect the Wavyrayed Lampmussel by disrupting host fish relationships. For example, the mottled sculpin has shown recruitment failure and steep declines in abundance in the Great Lakes basin since the introduction of the exotic round goby (Neogobius melanostomus) (Dubs and Corkum 1996, Jannsen and Jude 2001).
Impoundments: Damming of the stream channel has been shown to detrimentally affect mussels in many ways. Reservoirs alter downstream flow patterns and disrupt the natural thermal profiles of the watercourse while impoundments act as physical barriers potentially separating mussels from their host fish. Impoundments also act to increase water retention times thereby making river systems more susceptible to invasion by exotics such as the zebra mussel. Reservoirs with retention times greater than 20-30 days allow enough time for veligers to settle and act as seed populations for downstream sites (Metcalfe-Smith et al. 2000). Zebra mussels were reported from the Fanshawe Reservoir (UTRCA 2003) and Springbank Reservoir (pers. comm., S. Hohn, UTRCA, June 2003) on the Thames River during 2003 (UTRCA 2003). At present, both of these zebra mussel infestations are downstream of the most sections where Wavyrayed Lampmussels are found. Similar infestations, should they occur in Wildwood or Pittock reservoirs, higher up in the system could prove very harmful to the Wavyrayed Lampmussel populations in the North and South Thames. The Grand River is heavily impounded with 34 dams or weirs (GRCA 1998) and establishment of zebra mussels in the Luther, Belwood, Guelph, or Conestogo reservoirs could seriously impact the reach where the Wavyrayed Lampmussel is found.
Contaminants:Evidence suggests that mussels are sensitive to PCBs, DDT, Malathion and Rotenone that can inhibit respiration and accumulate in mussel tissue (USFWS 1994). PCBs have been detected in mussel tissue in the Middle Maitland River (pers. comm. D. Kenny, MVCA, July 2003). The glochidial stage appears to be particularly sensitive to heavy metals (Kellar and Zam 1990), ammonia (Goudreau et al. 1993; Mummert et al. 2003)), acidity (Huebner and Pynnonen 1992) and salinity (Liquori and Insler, as cited in USFWS 1994). Glochidia of the Wavyrayed Lampmussel were the most sensitive to copper of the five species tested by Jacobson et al. (1997). Copper levels exceed federal guidelines in several sub-basins of the Thames River in which the Wavyrayed Lampmussel is still found. Only the upper reaches of the Grand River have copper levels that fail to exceed the federal guidelines and these correspond to the only portions of the watershed where the Wavyrayed Lampmussel is found (Metcalfe-Smith et al. 2000). Copper levels exceed federal guidelines in the Middle Maitland River as well (pers. comm. D. Kenny, MVCA July 2003).
Nutrients: The primary land use in the Ausable and Sydenham River basins is agriculture. Row crops (corn, beans) predominate in the Ausable River watershed while cash crops dominate the Sydenham River watershed (Nelson 2000). Water quality in the Ausable River is generally considered poor resulting from agricultural runoff and manure seepage (ABCA 1995, ARRT 2003). In the Grand River, clearing of riparian vegetation and allowing livestock to access the river has resulted in poor water quality with increased sediment loads (WQB 1989a). Agricultural activity is expected to increase in the Grand River basin over the next 25 years leading to a predicted increase in sediment, pesticide, fertilizer, and manure runoff. Water quality in the Thames River basin has historically suffered greatly from agricultural activities. Tile drainage, wastewater drains, manure storage and spreading, and insufficient soil conservation have all contributed to poor water quality within the Thames basin (Metcalfe-Smith et al. 2000). Phosphorus and nitrogen loadings have increased steadily and some of the highest livestock loadings for the entire Great Lakes basin have been reported for the Thames River watershed (WQB 1989b). Mean ammonia concentrations in all sub-basins of the Thames River exceed the federal freshwater aquatic life guidelines (Metcalfe-Smith et al. 2000). It has recently been reported that juvenile freshwater mussels are among the most sensitive aquatic organisms to unionized ammonia toxicity, typically showing adverse responses at levels well below those used as guidelines for aquatic safety in U.S. waterways (Newton 2003; Newton et al. 2003). The recently discovered Maitland River population faces threats from agricultural run-off with 75% of nitrate samples on the Middle Maitland exceeding the federal guidelines for negatively impacting aquatic health while 56% of total phosphorus levels exceed those indicating a high likelihood of algal blooms (pers. comm. D. Kenny, MVCA, July 2003).
Disruption of Host Fish Relationship: Any factors that directly or indirectly affect host fish distributions will impact Wavyrayed Lampmussel distributions. Smallmouth bass, the likely host species, are very rare in the Sydenham River system (M. Poos, University of Guelph, cited in Metcalfe-Smith and McGoldrick 2003) which may explain the disappearance of Wavyrayed Lampmussels from this watershed. Smallmouth bass populations have also been reduced in the Grand River between Cambridge and West Montrose, likely as a result of angling pressure (Cooke et al. 1998).
Urbanization: The Grand River watershed has a population of approximately 780,000 and is expected to increase by nearly 40% over the next 20 years (GRCA 1998; Krause et al. 2001). More than 80% of the population occupies less than 7% of its area. Wastewater discharge is a major input in these urban areas and will only increase with increasing population. Within the Thames River basin all industrial outfalls and 70% of municipal outfalls are located within the heavily populated upper reaches where the Wavyrayed Lampmussel is found.
Recreational Activities: Reaches of the Grand River where Wavyrayed Lampmussels occur are popular areas for canoeists. Metcalfe-Smith et al. (2000) observed that paddlers in shallow water often disturbed the riverbed creating the potential for dislodging mussels and promoting downstream transport. Increasing popularity of recreational activities like canoeing may further increase stresses on unstable populations.
Predation: Predation by terrestrial predators such as muskrats (Ondatra zibethicus) and raccoons (Procyon lotor) has been shown to be an important limiting factor for some populations (Neves and Odom 1989). Neves and Odom (1989) reported that muskrats are both size and species specific predators and that they actively choose Wavyrayed Lampmussels when available. Metcalfe-Smith and McGoldrick (2003) reported observing raccoon predation on mussels in Ontario waters. Human-related activities, such as the adoption of conservation tillage practices, have resulted in surges in predator populations which may increase the importance of predation related threats in the future (Metcalfe-Smith and McGoldrick 2003). Southwestern Ontario farmers have reported a surge in raccoon numbers in recent years that may correspond with the adoption of conservation tillage practices (Metcalfe-Smith and McGoldrick 2003). This anecdotal observation needs verification in order to quantify the effects of human-related activities on predator populations.
|Ausable R.||Siltation, Water Quality|
|Grand R.||Host Fish, Urbanization|
|Lake St. Clair delta||Exotics (dreissenid mussels)|
|Thames R.||Water Quality; Siltation, Exotics|
|Great Lakes (extirpated)||Exotics (dreissenid mussels)|
|Sydenham R. (extirpated)||Siltation (disruption of reproductive cycle); Loss of Host|
- Date Modified: