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

I. Background - Habitat Role

12. Critical Habitat

Critical Habitat is defined in SARA as the habitat required for the survival or recovery of a listed species. 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 these species although Table 2 outlines activities that would assist with obtaining the required information. The activities listed in Table 2 are not exhaustive but outline the range and scope of actions identified by the OFMRT as necessary to identify critical habitat for all five species. 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 OFMRT has identified the areas listed in the Currently Occupied Habitat and Historically Occupied Habitat sections as areas in need of conservation.

Table 2: Schedule of activities to identify Critical Habitat for these five mussel species.
ActivityApproximate Time Frame1
Conduct mussel population surveys2006-2008
Assess habitat conditions in occupied areas (e.g., flow, substrate, water clarity and quality)2006-2008
Determine any life stage differences in habitat use2007-2009
Survey and map areas of suitable but unused habitat within historical range2008-2010
Assess genetic structure of populations2006-2008
Complete host fish studies2006-2008
Conduct host fish population surveys2006-2008
Assess habitat use by host species2006-2008
Determine areas of overlap between mussel and host habitat2009-2010

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

13. Habitat Trend

The loss of these five mussel species from historical habitat in the Lower Great Lakes region can be largely attributed to the detrimental effects of Dreissenid mussels including competition for food, resources and space. The introduction and spread of the zebra and quagga mussel throughout the Great Lakes in the late 1980s decimated native mussel populations (Schloesser et al.1996). 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). The continue presence of Dreissenid mussels throughout much of the historical range of these species results in large areas of formally suitable habitat remaining unavailable.

The Round Pigtoe was recently reported from three sites in the St Clair River delta; however, repeated sampling of the same sites reported declines in all three sites. Isolated patches of the Northern Riffleshell continue to survive in some nearshore wetland areas with very shallow water, a high degree of connectivity to the lake (which ensures access to host fishes), and harsh conditions for zebra mussels (high water temperatures and considerable wave action in summer; ice scour in winter). However, such “refugia” are rare, and most of the mussel habitat in the Great Lakes has been permanently lost (COSEWIC 2003).

The Northern Riffleshell and Snuffbox historically occurred in the Ausable, Grand and Thames rivers and may still have remnant populations in the Ausable and Thames rivers. The Round Pigtoe historically occurred in the Thames and Grand rivers, and remnant populations have been identified in both watersheds. The Mudpuppy Mussel and Rayed Bean historically only occurred in the Sydenham and Thames rivers. In the Ausable River, former habitat has been lost due to siltation, high turbidity levels, alterations to the flow regime, toxic contaminants, thermal changes, and exotic species. In the Grand River, untreated wastewater inputs from major urban centres likely contributed to the declines. In the Thames River, agricultural impacts such as siltation and turbidity, nutrient loading, toxic compounds, altered water flow, barriers to movement, as well as non-native species, and thermal pollution have all contributed to the degradation of habitat for these five mussel species.

14. 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 these mussels and against damaging or destroying its residences, as well as prohibitions on the destruction of Critical Habitat. The Fisheries Act represents an important tool for habitat protection and along with other federal environmental legislation is complementary to the Species at Risk Act. Under the federal Fisheries Act mussels are considered shellfish, falling under the definition of 'fish', and their habitat is therefore protected from harmful alteration, disruption or destruction unless authorized by the Minister of Fisheries and Oceans, or his/her delegate. Planning authorities must be consistent with the Provincial Policy Statement under Section 3 of Ontario's Planning Act, which prohibits development and site alteration in the significant habitat of endangered species. The Ontario Lakes and Rivers Improvement Act prohibits the impoundment or diversion of a watercourse if siltation will result while the voluntary Land Stewardship II program of the Ontario Ministry of Agriculture, Food and Rural Affairs is designed to reduce erosion on agricultural lands. Stream-side development in Ontario is managed through floodplain regulations enforced by local conservation authorities. Ontario Regulation 97/04 addresses “Development, Interference with Wetlands & Alteration to Shorelines & Watercourses.” This Regulation was enacted as a result of an amendment to Section 28 of the Conservation Authorities Act, and replaces the “Fill, Construction and Alteration to Waterways Regulation”. The Generic Regulation controls the following activities: development within a regulated area; interference and alterations to watercourses; interference and alteration to wetlands (defined by the Conservation Authorities Act); and Interference and alteration to shorelines.

15. 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.