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Recovery Strategy for the Hickorynut and the Kidneyshell [Final Version]

Habitat – Round Hickorynut


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 & 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 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.

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 substrate  (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


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 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.

 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.

 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 the distribution, quantity, and quality of habitat across the range of the species. At present, this information is not available for the Round Hickorynut 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 Hickorynut. 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 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
Determine host fish species2006
Conduct host fish population surveys2006-2008
Assess habitat use by host species2006-2008
Determine areas of overlap between mussel and host habitat2009-2010