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The Midwest Region includes Illinois, Indiana, Iowa, Michigan, Minnesota, Missouri, Ohio and Wisconsin. Find a location near you.


The Midwest Region includes Illinois, Indiana, Iowa, Michigan, Minnesota, Missouri, Ohio and Wisconsin.
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Scaleshell (Leptodea leptodon)

Final Recovery Plan (February 2010)


The Scaleshell Recovery Plan is a 131-page document. Below is the Executive Summary. Click here to download or view the entire Scaleshell Recovery Plan (PDF file 933KB).



Current Species Status:The scaleshell mussel (Leptodea leptodon) is a federally listed, endangered species that once occurred in 56 rivers in the Mississippi River Drainage. The species has undergone a dramatic reduction in range and is believed to be extirpated from 9 of the 13 states it historically occurred in. While the species has been documented from 18 streams in the last 25 years, it can only be found consistently in three streams in Missouri where it is still very rare.


Habitat Requirements and Limiting Factors: The scaleshell occurs in medium to large rivers with low to medium gradients. It primarily inhabits stable riffles and runs with gravel or mud substrate and moderate current velocity. The scaleshell requires good water quality, and is usually found where a diversity of other mussel species are concentrated. More specific habitat requirements of the scaleshell are unknown, particularly of the juvenile stage. Water quality degradation, sedimentation, channel destabilization, and habitat destruction are contributing to the decline of the scaleshell throughout its range. The spread of the non-native zebra mussel (Dreissena polymorpha) may threaten scaleshell populations in the near future.


The scaleshell must complete a parasitic phase on freshwater drum (Aplodinotus grunniens) to complete its life cycle. The scaleshell’s complex life cycle and extreme rarity hinders its ability to reproduce. The sedentary nature of the species and the low density of remaining populations exacerbate threats to its survival posed by the natural and manmade factors. Further, the relatively short life span of the scaleshell may render it less able to tolerate periods of poor recruitment. The remaining populations are very susceptible to local extirpation, with little chance of recolonization because of their scattered and isolated distribution.


Recovery Strategy:

Scope of threats and recovery: Streams occupied by the scaleshell have numerous and widespread threats affecting the species. In some cases, these threats are related to the surrounding land use and can originate far upstream of extant populations. Therefore, threats not only need to be addressed immediately adjacent to occupied sites, but also in the watershed upstream. Some recovery actions may need to be implemented on a large scale in order to restore aquatic habitat downstream. Recovery efforts on this scale will not be possible without soliciting outside help to restore aquatic habitat and improve surface lands. The assistance of federal and state agencies, conservation groups, local governments, private landowners, industries, businesses, and farming communities will be essential in implementing the necessary recovery actions for the scaleshell to meet recovery goals. The role of private landowners, nonprofit organizations, and corporations cannot be over emphasized as most land in watersheds occupied by the scaleshell is under private ownership.


Addressing threats: To solicit outside help and foster the many partnerships needed to address threats, a recovery implementation team will be formed. This team may be made up of species experts and representatives from federal and state wildlife agencies, other federal and state agencies, non-government organizations, academia, and other concerned groups with a diversity of expertise on conservation science and public relations within the scaleshell’s range. This team will take a strategic approach to address threats and work with willing partners to carry out the appropriate recovery actions to protect existing habitat, alleviate threats, and restore habitat. First, threats will be identified, assessed, and mapped for each watershed occupied by the scaleshell. Then a strategic recovery implementation database will be developed to guide recovery efforts for each population. The database will be used to prioritize populations, threats, and needed recovery actions as well as track recovery efforts and document when threats to each population have been alleviated. The threat mapping and strategic database are an integral part of the recovery strategy for the scaleshell.


Watershed improvements will be aimed at addressing the various causes of habitat degradation including sedimentation; point and non-point pollution sources; substrate destabilization; land, bank, and channel erosion; and eutrophication. Examples of watershed improvements to alleviate these threats include, but are not limited to the following: improving wastewater treatment plants, reestablishing protective riparian corridors to reduce sedimentation; stabilizing stream banks; reducing sheet run-off; using no-till agricultural methods; controlling nutrient enrichment by carefully planning heavy livestock use areas; excluding cattle from streams by erecting fences and providing alternative water supplies; development of gravel mining guidelines; and implementing voluntary best management practices to control run-off for a variety of agricultural, silvicultural, and construction activities.


Other factors that potentially will affect the scaleshell in the future include the introduction of non-native species, predation by small mammals, and mussel die-offs due to drought, contaminant spills, and disease. The scaleshell recovery implementation team will call on the nation’s leading experts to devise methods to reduce the likelihood of zebra mussel or black carp invasions into streams occupied by the scaleshell. Emergency response strategies will be developed that will outline response protocols to effectively deal with mussel kills and invasions of non-native species that do occur. Measures will also be taken to control predators at select sites where it is identified as a significant factor contributing to the scaleshell’s decline.


Because only a small number of scaleshell populations exist, it is essential that they all be protected. Utilizing existing legislation, regulations, and programs (i.e., ESA, CWA, FWCA, wetland and water quality regulations, stream alteration regulations, FERC relicensing, etc.) to protect the scaleshell and its habitat is a reasonable means to protect remaining scaleshell populations.


Sound science: Achieving the recovery goals and criteria outlined in this plan will also be dependent upon the application of sound science to make informed management decisions. Because the recovery implementation team will include species experts and experts in conservation science, it will serve in this capacity as well. The recovery implementation team will coordinate and oversee the implementation of the recovery objectives outlined in this plan. Other roles of the team include, but are not limited to the following: 1) determine the effectiveness of recovery actions and adapt management measures accordingly, 2) determine ongoing research needs, 3) interpret and apply scientific information and consult with appropriate experts to make sound and scientifically-based management decisions, 4) assist FWS in determining when reclassification/delisting is appropriate, and 5) assist FWS in conducting five-year reviews.


Artificial propagation: The remaining populations of the scaleshell are also in imminent danger of extirpation because of their extremely small size and isolated distribution. The small number and low density of remaining populations exacerbate threats to its survival posed by natural and manmade factors. Recruitment failures could lead to their extirpation, with little chance of recolonization, in a relatively short period of time because of the short life-span of the species. Therefore, augmenting existing populations through artificial propagation is considered necessary for the continued existence of the scaleshell. This is the most urgent recovery action at this time. The goal of a propagation program for the scaleshell is to augment and stabilize populations. Augmenting existing populations will help ensure populations persist long enough to allow habitat improvements to take effect and to permit further scientific study. Preventing further loss of populations may also preserve genetic diversity of the species.


Research: The successful recovery of the scaleshell mussel will depend on the extent of our knowledge of the species and the causes of its decline. Critical aspects of the biology, ecology, and genetics of the species will be investigated, the results of which will direct recovery actions and inform management decisions. Data will be collected on the tolerance of the scaleshell to specific pollutants and the occurrence of these chemicals in watersheds in order to focus efforts to minimize or eliminate them. Lastly, how various water quality and environmental impacts associated with the operation of dams will be investigated to inform conservation efforts to recover populations located downstream of these operations.


Recovery in historical range: Initial recovery efforts will focus on watersheds where extant populations exist in order protect and stabilize those populations. Once the recovery requirements are met to downlist the species to threatened, more restoration efforts will be shifted to additional areas of the scaleshell’s historical range to meet the recovery objectives to delist the species. Because improvements need to take place throughout entire watersheds, a long period of time will be required for habitat improvements to begin to have beneficial effects on populations and the habitat they depend on.


Public outreach: An outreach and education program will be carried out to heighten awareness of the scaleshell as an endangered species and to solicit outside help with recovery actions. Outreach material will be developed and produced to target the general public, schools, government agencies, congressionals, businesses, landowners, and other key partners needed to carry out the recovery actions. The goal of this outreach program is to increase appreciation for the scaleshell and provide information on how to become involved in recovery efforts. To increase the willingness of potential partners to participate in the recovery of the scaleshell, materials will highlight the many benefits of the scaleshell recovery actions such as cleaner water and improved health of the stream ecosystem overall.


Recovery Goals and Objectives: The ultimate goal of the recovery actions outlined in this plan is to reclassify and eventually delist the scaleshell. The objectives are to ensure the long-term viability of the scaleshell by stabilizing and protecting existing populations and restoring its habitat and watersheds it depends on. Recovery of the scaleshell in the near future is not likely because of the extreme rarity of the species, the extent of the decline that has occurred, and the large-scale of habitat restoration required to have a positive effect on populations.


Recovery Criteria: The scaleshell will be considered for downlisting to threatened status when the following criteria have been achieved:


1. Through protection of existing populations, successful establishment of reintroduced populations, or the discovery of additional populations, four stream populations exist, each in a separate watershed and each made up of at least four local populations located in distinct portions of the stream. Each stream population must exist in a separate watershed so that a single stochastic event, such as a toxic spill or disease outbreak, will not affect more than one of the four stream populations. This criterion is based on the available information and the best professional judgment of species experts (see Appendix v), and may be revised based on additional biological, demographic, or genetic information obtained through Recovery Actions 3.1 and 3.4.


2. Each local population in Criteria 1 is viable in terms of population size, age structure, recruitment, and persistence. Currently, what constitutes a viable population of the scaleshell is not known. Population viability will be defined when Action 3.4.2 (Research Population Dynamics of the Scaleshell) is completed. In the future, this criterion will be revised to incorporate the definition of population viability resulting from this recovery action (3.4.2).


3. Threats to local populations in Criterion 1 have been identified and addressed per the measurable criteria developed in Action 2.3. Currently it is not feasible to identify in this criterion the specific threats to populations and thresholds at which those threats are reduced to the level where criteria 1 and 2 are achieved. However, the thresholds for this criterion will be defined through the implementation of key actions in the plan as follows.


Step 1: Identify and map present and foreseeable threats to local populations in a GIS database (Action 2.2).

Step 2: Define measurable criteria for alleviating/reducing each of those threats and prioritize threats according to effects to local populations (Action 2.3).

Step 3: Apply the appropriate recovery actions outlined in this plan to alleviate/reduce threats.

Step 4: Track the progress of recovery implementation (Action 7.2).
The scaleshell will be considered for removal from the protection of the Endangered Species Act when the following criteria are achieved:


Actions Needed: Recovery actions needed for the scaleshell include: 1) stabilize existing populations through artificial propagation to prevent extirpation; 2) formation of partnerships and utilization of existing programs to protect remaining populations, restore habitat, and improve surface lands; 3) improve understanding of the biology and ecology of the scaleshell; 4) further delineate the current status and distribution of the scaleshell; 5) restore degraded habitat in areas of historical range; 6) reintroduce the scaleshell into portions of its former range; 7) initiate various educational and public outreach actions to heighten awareness of the scaleshell as an endangered species and solicit help with recovery actions; and 8) track recovery and conduct periodic evaluations with respect to recovery criteria.


The Scaleshell Recovery Plan is a 131-page document. Above is the Executive Summary. Click here to download or view a PDF file of the complete Scaleshell Recovery Plan.


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