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

II. Recovery

1. Recovery Goals

The long-term goals of this recovery strategy are:

  1. to prevent the extirpation of the Northern Riffleshell, Snuffbox, Round Pigtoe, Mudpuppy Mussel and Rayed in Canada;
  2. to return healthy self-sustaining Northern Riffleshell populations to the Ausable, Grand, Sydenham and Thames rivers and the Lake St. Clair delta and;
  3. to return healthy self-sustaining populations of Snuffbox to the Ausable, Grand, Sydenham and Thames rivers and the Lake St. Clair delta.
  4. to return healthy self-sustaining populations of Round Pigtoe to the Sydenham, Thames and Grand rivers and the St. Clair delta and;
  5. to return healthy self-sustaining populations of Mudpuppy Mussel to the Sydenham and Thames rivers and Lake St. Clair delta and;
  6. to return healthy self-sustaining populations of Rayed Bean to the Sydenham and Thames rivers and Lake St. Clair delta;

These populations will only be considered recovered when they have returned to historically estimated ranges and/or population densities and are showing signs of reproduction and recruitment.

2. Recovery Objectives (5 year)

  1. Determine extent, abundance and population demographics of existing populations.
  2. Determine fish hosts and their distributions and abundances.
  3. Define key habitat requirements to identify critical habitat.
  4. Establish a long-term monitoring program for all species, their hosts and the habitats of both.
  5. Identify threats, evaluate their relative importance and implement remedial actions to minimize their impacts.
  6. Examine the feasibility of relocations, reintroductions and the establishment of managed refuge sites.
  7. Increase awareness about the distribution, threats and recovery of these species.

 3. Approaches to Meeting Recovery Objectives

The approaches to recovery have been organized into four distinct categories – research and monitoring, management, stewardship and awareness. Successful recovery will require consideration of approaches from all categories. A narrative has been included after each table where appropriate.

a) Research and Monitoring Approaches
PriorityNoObjective Addre-ssedBroad Approach/-StrategySpecific StepsAnticipated EffectThreat Addresse
Urgent1-1ii, vResearch – host fish.Continue fish host testing for the Snuffbox, Northern Riffleshell, Round Pigtoe and Rayed Bean. Will help determine if host abundance is limiting factor for the four mussel species. Will assist with identifying critical habitat. Host Fishes
Urgent1-2ii, vSurveys – host fish.Determine the distribution and abundance of the host species.Will help determine if host abundance is limiting the five mussel species.Host Fishes
Urgent1-3iiiResearch – Critical Habitat.Determine the habitat requir-ements for all life stages. Will assist with defining critical habitat for the Mudpuppy Mussel, Northern Riffleshell, Round Pigtoe, Rayed Bean and Snuffbox. 
Urgent1-4iii, viSurveys – Critical Habitat.Prepare a distribution map of areas of suitable habitat.Will assist with identifying critical habitat and potential areas of reintroduction.  
Urgent1-5viResearch – managed refuge sites.Investigate the feasibility of establishing actively managedrefuge sites in the St. Clair delta. Will determine if the Northern Riffleshell and Round Pigtoe in the St. Clair delta can be insulated from the effects of zebra mussels.Exotic Species
Urgent1-6viPopulation augmentationExamine the feasibility of translocations and re-introductions.Will determine if small populations can be augmented or if the species can be reintroduced in historical range. 
Necessary1-7i, ivMonitoring – mussel and fish host populations.Establish a network of permanent monitoring stations throughout historic and present ranges.Will permit tracking of populations, analysis of trend patterns, and permit the evaluation of recovery actions. 
Necessary1-8iv, vMonitoring – habitat.Establish permanent monitoring sites for tracking changes in habitat.Provides trend data for key habitat and will help evaluate the relative threat of habitat loss. 
Necessary1-9vResearch – threats.Identify and evaluate threats to all life stages.Will assist with determining reasons for declines and devel-oping remedial actions.All threats.
Necessary1-10viResearch – conservation genetics.Compare the within and among population genetic variability of Canadian populations and determine if populations show genetic structure by comparing variability between populations in Canadian and U.S. waterways.Will assist with determining if population transl-ocation or augmentation is appropriate. 

1-1 & 1-2: The necessity for a period of encystment represents a potential bottleneck in the lifecycle of the mussel.  Research and recovery actions focusing on the pre or post encystment period may prove unproductive if the presence of a host fish is the limiting step. In order to determine if these species are host limited it is necessary to first identify the host species and then to confirm that the distributions of the mussel and its host overlap in time and space in a manner that will permit successful encystment. The identification of high host specificity in some mussel species requires that hosts be identified for local populations whenever possible. It is already well documented that the Mudpuppy Mussel is host specific with the mudpuppy.  Host species for Canadian populations of the Northern Riffleshell, Rayed Bean and Snuffbox have been identified, however, further testing should continue as results are still in progress for the Northern Riffleshell and Snuffbox (McNichols and Mackie 2004). Host species for Canadian populations of the Round Pigtoe are based on results from the United States. Once the Canadian hosts have been confirmed for these species it is necessary to ensure that host species distributions overlap with the mussel distributions. Since adult mussels are essentially sessile this can be accomplished by confirming that members of the hosts species occur in reaches with mature female mussels at times when the female mussels possess mature glochidia.

1-3 & 1-4: Determination of critical habitat is an essential component in the recovery of these species.  Although adult mussels are relatively passively distributed, distinct habitat types can be associated with adult distributions suggesting that survival is linked to local habitat conditions.  Habitat conditions may be equally important during the juvenile stage and attention must also be paid to the habitat preferences of the hosts. Identification of critical habitat will be a multi-stage process. For more information on the required steps see Critical Habitat sections for each species.

1-5:  Remnant populations of both Northern Riffleshells and Round Pigtoes can be found in the delta area of Lake St. Clair despite the presence of zebra mussels.  Metcalfe-Smith et al. (2004) reported zebra mussel infestation rates ranging from <1 to 36 zebra mussels/unionid in this area during 2003. While this rate of infestation is below the lethal limits reported elsewhere (Ricciardi et al. 1995) it may be resulting in long term chronic effects that are causing prolonged declines. Comparisons of collections made in 2001 with those in 2003 showed that abundance of all unionids had declined by about 14% while declines were much higher for some species (i.e., 80% decline of round hickorynut) (Metcalfe-Smith et al. 2004).   Although the overall trend was toward declining unionid densities some sites showed stable overall abundances. These sites were associated with low zebra mussel infestation rates and high unionid diversity and may represent potential refuge sites. Since these sites are still affected by zebra mussels it is likely that unionids will need to be actively managed with regular zebra mussel removal and the active relocation of riffleshells and other mussel SAR to these locations from the more heavily infested sites.

1-7 & 1-8: A network of detailed, permanent monitoring stations should be established throughout the present and historic ranges of the five mussel species. Monitoring sites should be established in a manner so as to permit:

  • Quantitative tracking of changes in mussel abundance or demographics (size distribution, age structure etc.) or that of their hosts.
  • Detailed analyses of habitat use and the ability to track changes in use or availability.
  • The ability to detect the presence of exotic species (i.e. zebra mussels). Reservoirs represent the likely seed locations for zebra mussels in the Grand, Thames, Sydenham and Ausable rivers. Monitoring sites should be established within or close to these reservoirs to permit the early detection of zebra mussels in the event that they invade these systems.  Monitoring of exotics in the Lake St. Clair delta will likely be conducted in close association with the managed refuge sites.