Introduction 



Unionid mussels are considered among the most 

 endangered faunal groups inhabiting the United States 

 (Shannon et al. 1993; Neves 1993). Fifty-one species of 

 mussels occurred historically in the Upper Mississippi 

 River (UMR)--a substantial portion (17 ^c) of the 297 taxa 

 of freshwater mussels found in North America (Turgeon 

 et al. 1988). In the UMR there are currently 18 mussel 

 species listed as threatened or endangered includmg three 

 federally endangered mussel species, Lampsilis higginsi, 

 Potamilas capax, and Quadrula fragosa (Page et al. 

 1991). Mussel populations in the UMR have been subject 

 to a number of stresses, including (1) heavy commercial 

 harvesting formerly for the production of pearl buttons 

 and more recently to supply raw shell for the Japanese 

 cultured pearl industry, (2) pollution from both urban 

 centers and nonpoint sources, and (3) modification of the 

 river for navigation (Sparks and Blodgett 1983; Sparks 

 and Blodgett 1988). Between 1982 and 1986 massive die- 

 offs of mussels occurred in the UMR (Neves 1987, 

 Blodgett and Sparks 1987 a, b). Although the die-offs 

 were investigated, the causes were never identified 

 (Sparks et al. 1990). 



In response to the widespread mussel dieoffs and 

 increasing commercial harvest, the Illinois Department of 

 Conservation designated seven areas in the Illinois portion 

 of the Mississippi River as mussel refuges in July 1988 

 (Figure 1). The primary objectives of these refuges were 

 to (1) protect endangered or threatened mussels, (2) 

 provide a seed source to repopulate other areas, and (3) 

 serve as imharvested reference areas for comparison with 

 harvested areas. If populations in the harvested areas 

 declined while those in the refuges maintained themselves 

 or increased, then more stringent harvest regulations 

 might be indicated. If populations in both areas declined, 

 then other factors should be investigated, such as poor 

 water or sediment quality, parasites, disease, or declines 

 in the fishes that host and disperse the glochidia (larvae) 

 of the mussels. 



Critical information concerning the life-history 

 parameters and population dynamics of freshwater mussels 

 is often lacking and desperately needed for the sound 

 management and conservation of this resource. The need 

 is especially crucial for commercially harvested species. 

 Current regulations governing the commercial mussel 

 harvest (e.g., legal species, minimum shell size, or 

 season) are based on inadequate scientific information and 

 typically reflect preferences of the shelling industry (Thiel 

 and Fritz 1993). Monitoring and evaluation of the 

 resource throughout the UMR rely heavily on annual shell 



buyers reports. The UMR states have yet to establish 

 uniform regulations to govern commercial mussel harvest. 

 The current system which regulates and monitors 

 commercial mussel harvest in the UMR is antiquated, 

 based on inadequate scientific information, and in 

 desperate need of review and reform. It is especially 

 important to reevaluate current mussel regulations and 

 conservation strategies now that zebra mussels have been 

 found in the Mississippi River. The U.S. Fish and 

 Wildlife Service has predicted 20 species of mussels in 

 North America will become extinct over the next few 

 years as a result of the zebra mussel invasion (Biggins 

 1992). Many difficult management decisions will likely 

 be made in the coming years in attempts to preserve and 

 protect the remaining mussel resource. Without reliable 

 scientific information, management decisions may be 

 ineffective or even cause further harm to mussel 

 populations. 



The objectives of the comprehensive evaluation 

 of Reach 15 mussel beds were to assess the status of 

 harvested and unharvested (refuge) mussel beds by 

 evaluating the following parameters: (1) species 

 abundance and richness, (2) recruitment, (3) age and 

 growth, (4) mortality, and (5) status and impacts of newly 

 introduced zebra mussels. Long-term population trends 

 were evaluated by comparison of results with those from 

 previous scientific mussel surveys conducted in Reach 15. 



Methods 



Study Sites 



During 1994 and 1995, we quantitatively sampled 

 three mussel beds in Reach 15 of the UMR near Moline, 

 Illinois (Figure 2). One mussel bed. Sylvan Slough 

 (rivermile [RM] 485.8), was located within a mussel 

 refuge established in 1988; harvesting mussels in the 

 refuge is illegal. Two mussel beds, Case-IH (RM 488.5) 

 and Illiniwek (RM 492.4), are known to be commercially 

 harvested (Figure 2). A more detailed description and 

 location of each study site follows. 



(1) Sylvan Slough (RM 485.8): (Figure 3) - This site 

 was chosen as a reference or unhar\ested site. It was 

 designated as one of the seven mussel refuges in July 

 1988 (Figure 1). Quantitative mussel collections were 

 made at this site during 1983, 1985, and 1987 by the 

 Illinois Natural History Survey (Sparks and Blodgett 

 1983, Blodgett and Sparks 1987a and 1987b). These 

 previous surveys reported an abundant mussels population 



