(3) Develop population models to guide and assist the 

 management of mussels. Mussel populations are in 

 urgent need of protection and management, but there is a 

 lack of information on which sound management practices 

 could be based. Among the very basic questions which 

 need to be answered are: are mussel populations 

 undergoing long-term decline? If so, what are the 

 contributing factors and their relative importance. For 

 example, is the problem caused by reduced recruitment, 

 increased mortality (due to harvest, zebra mussels, and 

 natural causes), or some combination of both? What is a 

 sustainable harvest level? What age classes or size classes 

 should be protected from harvest? These are the types of 

 questions addressed by population models that are in 

 common use in fish and wildlife management, e.g., for 

 managing the deer herd in Illinois. Similar population 

 models need to be developed to guide and assist the 

 management of mussels. 



The recommended approach in developing these 

 models is to gather data that will be immediately useful to 

 resource managers in the UMR in regulating harvest of all 

 commercial species, but at the same time begin 

 development of a population model for one commercial 

 species. Field and laboratory data would be used in the 

 model, which would eventually simulate the outcome of 

 various management decisions and varying degrees of 

 zebra mussel impacts. The initial model should be for A. 

 plicata (Threeridge) which makes up most of the 

 commercial harvest in the UMR and is common to most 

 of the medium and large rivers of the midwest. The exact 

 modeling approach should be left to the discretion of the 

 modeler, but an example is the dynamic pool approach 

 described by Pitcher and Hart (1982). 



Although a crude model can probably be 

 developed in one year, refinement, calibration, and 

 verification of the model is likely to take longer, 

 especially since it will require at least 5 years of field 

 work, perhaps more. The reasons for such a long-term 

 program are: (1) a long time series of data is required to 

 capture sporadic recruitment events and associate these 

 with causative factors, and (2) it will take a long time to 

 collect data that were not collected in earlier studies 

 (fecundity, age/shell length relationships, repeated 

 measures of marked individuals to determine growth). A 

 long-term commitment should be made to this program, 

 because it would be a waste of resources to start a 5-year 

 growth study involving recapture of marked mussels and 

 then not complete it because of lack of funding. 



Improved management of mussels does not have 

 to be postponed until the model is completed however, 

 because the field investigations themselves would provide 



useful information on the status of mussel populations. 

 The technical basis for management decisions should 

 improve rapidly as the model and its information base 

 improve year to year. 



(4) Monitor zebra mussel densities and impacts on 

 native mussels in the Mississippi River. Zebra mussel 

 densities and infestation of native unionid mussels have 

 increased significantly since 1994. Between July 1994 

 and July 1995, zebra mussel densities at the Illiniwek 

 study site increased from a mean of 1.5/m- to 2,519/m- 

 (Table H-1) and infestation of native unionids increased 

 from less than 1% to 48.9% (Figure H-2). As zebra 

 mussel densities and unionid infestation continue to 

 increase so will the likelihood of widespread unionid 

 mortality. Without continuation of monitoring of 

 Mississippi River zebra mussel populations to determine 

 abundance and their effects on native unionid mussels, it 

 will be difficult to justify the implementation of future 

 mitigation strategies. Reach 15 would serve as an ideal 

 location to continue to monitor the buildup and impacts of 

 zebra mussel populations since we have quantitative 

 baseline information on their abundance and infestation of 

 unionids. 



Acknowledgements 



Funding for this research was provided by the 

 former Illinois Department of Conservation (IDOC) 

 (contract number PC 955391) which was reorganized into 

 the Illinois Department of Natural Resources (IDNR) 

 effective 1 July 1995. Additional support was provided 

 by the Illinois Natural History Survey (INHS) and the 

 Upper Mississippi River System Long Term Resource 

 Monitoring Program (LTRMP), a cooperative effort of 

 the U.S. Army Corps of Engineers, National Biological 

 Service, and natural resource agencies of Illinois, Iowa, 

 Minnesota, Missouri, and Wisconsin. 



We are indebted to Peggy Baker representing 

 Tennessee Shell Company; to Wayne Davis representing 

 the Kentucky Fish and Wildlife Resources and the Mussel 

 Mitigation Trust Fund; and to Michael Vanderford 

 representing the National Fish and Wildlife Foundation 

 for their early financial support which allowed us to hire 

 the necessary personnel and purchase sampling equipment 

 utilized in the Reach 15 study. 



We are grateful to IDNR commercial fisheries 

 biologist Bob Williamson and former commercial fisheries 

 biologist Don Dufford for their support. We are indebted 

 to Bob Schanzle of the IDNR for his assistance as a diver 

 and willingness to lend a hand whenever needed. 



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