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Recovery Strategy For Northern Riffleshell, Snuffbox, Round Pigtoe, Mudpuppy Mussel and Rayed Bean in Canada [Proposed]

7. Habitat: Northern Riffleshell

Habitat Identification:The Northern Riffleshell lives mainly in highly oxygenated riffle areas of rivers (Clarke 1981; Cummings and Mayer 1992). The preferred substrate has been described as rocky and sandy bottoms with firmly packed sand and fine to coarse gravel. Recent observations have confirmed this in the Sydenham River. The Northern Riffleshell occurs in streams of various sizes and its existence in the western basin of Lake Erie was apparently due to sufficient wave action to produce continuously moving water (USFWS 1994). There is no information of thermal tolerance of the Northern Riffleshell, however, water temperatures at sites where live specimens were found in the Sydenham and Ausable rivers in 1997-1998 ranged from 18-27°C. The extent of preferred habitat in the 50-km reach of the East branch of the Sydenham River where this species still occurs has a relatively diverse substrate and associated habitat with well-defined riffles and pools, which create exceptional habitat for native mussels (Dextrase et al. 2003).

Currently Occupied Habitat: Habitat in need of conservation for the all five mussel species has been geospatially located using the methods developed by McGoldrick et al (in press) (Figures 16 & 17) 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 (in press) recommend using a 5km buffer around known species occurrences. The 5km 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.

Geospatial Description: Currently occupied habitat for the Northern Riffleshell can be defined as a 50 km reach of the East Sydenham River (Figure 16) where the Northern Riffleshell is currently found live as well as a 55 km stretch of the Ausable River (Figure 16) and small portion of the St. Clair delta (Figure 17).

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 packed sand or fine to coarse gravel and  

·   steady to moderate flows (riverine populations only)

·   well-oxygenated riffle areas or

·   nearshore areas with firm sand substrate (Great Lakes populations).

Activities Likely to Impact Currently Occupied Habitat

The currently occupied habitat of the Northern Riffleshell 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 Northern Riffleshell 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 (May 1 – December 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 for the Northern Riffleshell includes a portion of the lower Ausable River, the Detroit River and the western basin of Lake Erie.  Figure16

Figure 16: Currently occupied habitat of the Northern Riffleshell in the Sydenham and Ausable rivers.


Figure 17: Currently occupied habitat of the Northern Riffleshell in the Lake St. Clair delta.