V ILLINOIS NATURAL HISTORY SURVEY fcrot ' Analysis of a JVj usseljIDig-off \ n Pools 14 and 15 of theDpper M^sTssippi River Aquatic Biology Section Technical Report K. D. Blodgett and R. E. Sparks Report submitted to Non-game Check-off Program, Illinois Department of Conservation Aquatic Biology Technical Report 87/15 J BACKGROUND According to Fuller (1980) , early mussel surveys on the Upper Mississippi River by Tyron (1865), Pratt (1886), and Coker (1919) recorded a total of 48 species, and surveys on the Illinois River by Calkins (1874), Kelly (1899), Baker (1906), Forbes and Richardson (1913) , Danglade (1914) , and Richardson (1928) recorded 45 species. However, modern surveys by Fink (1966) and Fuller (1978, 1980) show a 23% decline in the number of species in the Mississippi (37 species left) , and Starrett (1971) reported a 44% decline in the Illinois (25 left) . Since the 1950' s, freshwater mussels have been harvested from the Mississippi drainage for use in the cultured pearl industry in Japan. In 1984, prices climbed to $800/ton of shells, stimulating exceptionally heavy harvesting; commercial shellers came from as far away as Texas and Oklahoma (Ballenger 1986) . The discovery of pearls of exceptional value in Wisconsin and near Grafton, Illinois (Fritz 1986) , apparently caused many commercial shellers to open every mussel they took, instead of culling undersize individuals back into the rivers (personal observation) . Since 1982, mussels in the Upper Mississippi River drainage have been affected by unexplained die-offs with the largest die- offs apparently occurring in 1982 and 1985 (Blodgett and Sparks 1987, Thiel 1987, Havlik 1987, Ballenger 1987). To date, no die- offs have been reported in the Illinois drainage, but die-offs have occurred in other major tributaries of the Mississippi River (Neves 1987) . In spring 1983, Arnold "Bill" Fritz, Commercial Fisheries Biologist, Illinois Department of Conservation, received a number 1 of reports from commercial shellers using diving gear that there were large numbers of freshly dead and dying mussels in the Mississippi River from Pool 12 downstream to Pool 19. At his request, the Illinois Natural History Survey (INHS) sampled known mussel beds in pools 14 and 15 near Rock Island, IL, in spring 1983 to document and quantify the die-off. During summer 1985, shellers again reported finding many recently dead mussels and we resampled Pool 15 in the fall. This report analyzes data collected in 1983 and 1985 and compares results of these collections with composition and density data collected by NUS Corporation in 1978 (Oblad 1979) . METHODS We quantitatively sampled mussels using a 24-ft pontoon boat modified to support surface-supply diving (Figure 1) and techniques developed during prior mussel research (Sparks and Blodgett 1983) . Divers placed all mussels and loose substrate from 1.0-m2 sampling frames into canvas collecting bags (Figure 2) and sent them to the surface where shells were sorted to species, measured, and categorized based on the following criteria: Live (LI) - soft parts intact; if valves gaped, they closed when prodded. Recently Dead (RD) - if soft parts were present, they were unable to close valves when prodded; if soft parts were gone, periostracum was intact; valves firmly joined by hinge ligament; interior nacre shiny (not the least bit chalky) . Old Dead (OD) - soft parts lacking; valves joined; periostracum incomplete; nacre chalky. Other - not meeting the above criteria — subfossil shells, valves not joined, etc. IfflB^^^:1 ill Digitized by the Internet Archive in 2010 with funding from CARLI: Consortium of Academic and Research Libraries in Illinois http://www.archive.org/details/analysisofmusselOOspar -0 a (0 a o IW 4J id H a en c •H > •H T3 13 0) •H H a • a w 3 a> Ifl R 1 nj a) U u j-f\jf\jo •— *— «— oomooo*— o*-roojrocoKivj(\ioof\iroo (M i- i- O- O O N-K>KltA>OCOOhO«-rOO Kl r- «- GO «- r- r-oo o oooo moo ooooo P O O O O OOOO N-OO CD O O O la fO f\ju~t o oo in mo oo oF» nj- fs-v3'OOO0*OO,NTO0>*Or^.-s*,OO^J'0^O0^C0 CM oooooooooooornoooocuooo co or\ioocDLOOLr>c\JOLnocO(>JOorMf\JOLnco co •-OOOOOOOOOOO^OOOOOfMOOO 1*1 ■sj-T— ooof\joc\it— orvjo^t— o o »— o^orvjNi m CO^vTOOOOOO*4-0*0»— OLnOOOCOO^J- <\J r- OOOOOOOOOOOOJOOOOOOOO t- cor\jr\jooooooc\ju"tO{\iomooocoo(\j co POOOOOOOOOOOOi-OOOOOt-OO S^ *—»—»— oooooo*— r\iOLnor\joooN-o«— *— •* Kl OOJLOOOOOOOCO ^r ro ofMcooooooocd *X Nl AJK)tA OlAKiOrO (MO»4,OOOOOOO0**ON.vtOO**N.sJ-O'**' «4" «— OOOOOOOOOOO*— OOOOOOOO CM oorvJoooooooLnoLnr\ioo(vjocoo(\j oo r\jooooooooooof\joooo^-ooo n! 00O«— OOOOOOOOJOOi— o o «- -^ ro o «— »• O'OLnoooooo^cooN-^-vj'OocNjrooo «— ooooooooooooooooo*— «— oo m Lnomoooooor\jcooor\jf\jooocooo f\j rjooooooooo*— o>4"Oooo«— «— oo c*j OOfNJOOOOOO*— N-OnO*— »-00nJN-00 o ro B § v> ( 5 8 OJ o L. u ml ID ro u flj *-l ( r '- o 8, 0 n i a — * +-* 3 3 -) .^ .^ ro T) tj ■B V H a J ) ) } ti- a a o a H >— 10 1985 We collected 21 species of live mussels from Pool 15 in 1985. The mean density of live mussels/m^ from the bed at RM 486.0 in 1985 was 100.1 (SD = 21.6, range = 69-132) (Table 4). The percent recently dead for all species combined was 17.9% (175 of 976). Mortality was 22.8% (23 of 101) for A. plicata and 21.9% (30 of 137) for M. gigantea. Mortality probably was not biased upwards by shellers because they could sell recently dead shells in 1985 (D.E. Ballenger 1986). The site at RM 488.6 had the highest average density of live mussels we had ever observed (139. 3/m2, Table 4). One 1-m2 frame contained 216 live mussels, another 213, and we discarded a sample with even more when both the diver and sampling frame were accidentally pulled away from the sample plot before completion of sampling. Distribution of live mussels between 1-m2 samples was uneven, as can be seen from the range of 62-216 and the standard deviation of 62.1. COMPARISONS BETWEEN SITES AND YEARS Oblad (1979) reported that SCUBA diving collections by NUS corporation in 1978 produced 25 live mussel species and a mean density of 13.6/m2 in two 12.2 x 21.4 m plots (522.2 m2 sampled) in Sylvan Slough near river mile 485.8 (Table 5). INHS sampling at the mouth of Sylvan Slough (RM 486.0) in both 1983 and 1985 produced fewer species but higher densities (Table 5) . Differences in densities between the study by NUS and INHS could be attributed to patchy distributions of mussels within the bed. The area sampled in 1978 by NUS may have been in a less dense part of the bed. 11 o o *— oovjoh-roo ooooh-m«-o 0^OOO■NtOOfMOC0*-TOOOO^O^*'^0^'^■ «— OOOOOOr-0«-OOOOOOOi— O N O C0OOOf\IOOOOOf\JOOOOOOC0(\JO(\l f\JOOOOOO*-0»— OOOOOOO*— OfVJO N-ooo»-oo>oo^o«-oooooo«— *- <\j »— roooinocO'-coinojoinor^T-inincoorocNj r^o-stocoor-oorgrvjoovj-T-oo-j-fMsjin >o o ro o l^ N N N fO N O t- O O (\J roo(\ih*roiAN-oororo oo^oooorvjfMN-s* CO O O (M fNJOi^-j-roroNOh- co o r-- o o o COON-ON-KlOOflfM (\JOOOOOO*-0-J- h"»oroot*io*-h.r\j»o OOOOOO^Oi— «- OOmO*J-*-OC\l*-C0O*-O*-O«-OO^s0^0 r\jooooooT-orov-ooooooNOO(\ji- K>o-sjoro«-oo«-ocOi-o<— o<—o ro «- ro ooco-^ooinoo-'srr^oroKii^N.<-K)f\Joor^hO (MOi-orMooroo^ruoooo-sjo^o^^ o «- OOOOrOvJOO<\IO*000*r-*0(NJ o «- 00 N- K) f\J vj N- .- (M O *- Crt CD -) o 0 re 111 a I ( CJ a i H 0 u o ,2 C/l E H c ro > (i ■i ro 3 > r -i r ra CJ CO ) Tl c i n CJ ro 01 0 ■i ) E [ ti n VI CD cu D => CO CD CD CD — ' -* .„ ,„ "1 3 "I "I ._ .^ F F c_ tD <0 11 Tl Tl V c c C-* w to (0 CI) re ■1 3 o 0 ■i 3 3 3 L. l_ a. a. CJ a CJ u t— *- CI) — 12 Table 5. Species and mean densities of live mussels collected near the mouth of Sylvan Slough, Pool 15, Mississippi River, in 1978 by NUS Corporation (RM 485.8) and in 1983 and 1985 by the Illinois Natural History Survey (RM 486.0) . NUS 1978 INHS 1983 INHS 1985 Actinonaias ligamentina Amblema plicata Anodonta grandis Anodonta imbecillis Arcidens confragosus Cumberlandia monodonta Ellipsaria lineolata Elliptio dilatata Fusconaia ebena Fusconaia flava Lampsilis higginsi Lampsilis radiata Lampsilis teres Lampsilis ventricosa Lasmigona complanata Leptodea f ragilis Ligumia recta Megalonaias gigantea Obliquaria reflexa Obovaria olivaria Plethobasus cyphyus Potamilus alatus Potamilus laevissima Quadrula metanevra Quadrula nodulata Quadrula pustulosa Quadrula quadrula Strophitus undulatus Tritogonia verrucosa Truncilla donaciformis Truncilla truncata Number of species Mean density (no./m2) P P P Aa P P P A Aa P P Aa Aa P P P P P P P P P Aa P P P P P Aa P P 24 13.6 A P P P P P P Aa A P A A A P A P P P P A A P A P Aa P P A A P P 89.5 A P P P P A P A A P A A A P A P P P P P P P P P P P P A A P P 21 100.1 P = present A = absent a recently dead collected, however no live specimens observed a total number of live species = 26 13 In 1983, there were no significant differences in live mussel densities or mortalities between the two sites (RM 494.6 and RM 494.7) in Pool 14. However, Pool 14 had a significantly lower density of live mussels (P = 0.01) and significantly higher mortality (P = 0.004) than Pool 15 (Table 3). The mortality of 6.3% (56 of 892) at RM 488.6 was significantly lower (P < 0.001) than at 486.0 (17.9%, 175 of 976) in 1985 (Table 4) . Densities of live mussels were not significantly different. Site 488.6 was nearer the main channel where higher current velocities may have scoured away more recently and old dead shells than at the other site, perhaps depositing some downstream at RM 486.0. A less likely explanation is that the die-off was less severe in this bed than in the one just 2.6 miles downstream. The significant difference (P < 0.001) in mortality at RM 486.0 between 1983 (30.4% RD) and 1985 (17.9% RD) may be attributable to shellers leaving recently dead shells in 1983 but harvesting them in 1985. The problem of separating the effects of selective harvest from those of a die-off illustrates the need to establish mussel preserves where harvesting would not be permitted. If shelling had no effect on the proportion of recently dead shells, a second hypothesis is that susceptible mussels died in response to some causative agent in 1983 leaving behind only more resistant mussels in 1985. A third hypothesis is that the intensity of some unidentified causative agent was less in 1985 than in 1983. 14 SIZE-SPECIFIC MORTALITY Length-frequency histograms for five of the more numerous species, Amblema plicata, Meaalonaias gigantea, Ouadrula pustulosa, Ellipsaria lineolata, and Leptodea fragilis, were skewed to the right, indicating that there were more large individuals in the population (Figure 4) . Similar skewed length frequencies have been reported from the Upper Mississippi River (Duncan and Thiel 1983; Coon et al. 1977). This skew is probably- due, in part, to the fact that intervals on the right contain large, slow-growing individuals, hence multiple year classes, while intervals on the left contain small, rapidly-growing individuals, hence fewer year classes. Commercial harvesting reduces the number of large individuals of Amblema plicata and Meaalonaias gigantea, so undisturbed populations of these mussels are even more skewed toward large individuals. In future collections, we will age mussels and measure shell lengths to determine how many year classes are included in each size interval. Aging should be done routinely in mussel studies, so that recruitment and survival rates can be determined. Larger size classes had higher mortality rates than smaller ones in most species (Figure 5) . Mortality was significantly greater (P < 0.08) in reproductive adults than in juveniles of Amblema plicata, Ouadrula pustulosa, and Megalonaias gigantea (Table 6) . Mortality rates may be greater in older individuals because of stresses associated with reproduction or a greater body burden of toxicants. Again, more data on size-specific natural mortality rates and body burdens of contaminants in healthy, undisturbed mussel populations are needed for comparison. 15 Amblema plicata 0.5 1.5 2.: 4.5 5.5 C.5 7.5 9.5 10.5 11.5 12.5 Lonuth Interval inanlmurn (tin) ZZ) Uy. \2222 Recently dead Quadvxila pustxilosa Length Interval maximum (cm) ZZ) Live ZZJ Recently dead Figure 4. Length-percent live and recently dead Amblema plicata and Quadrula pustulosa collected from pools 14 and 15 of the Upper Mississippi River in 1983 and 1985. Numbers at the top of bars indicate total number of live and recently dead in that interval. Horizontal bar below x axis indicates legal size range for commercial harvest. 16 Amblema plicata Quudrulu puatxilosa Figure 5. Percent recently dead, RD/(LI + RD) , for length intervals of Amblema plicata and Ouadrula pustulosa collected from pools 14 and 15 of the Upper Mississippi River in 1983 and 1985. Numbers at the top of bars indicate total number of live and recently dead in that length interval. Horizontal bar below x axis indicates legal size range for commercial harvest. 17 II r- ro o o o o -J N-' 1 1 P. 5 «- 1- f\i C -J- 1 s o o o o o o «- «- -o ro <- nl N C ij 1 1 n ra 0 o 1 rj -1 3 (Q m J i g T) i 1 o »- -n 5 3 8. — c 2 Y 2 18 Detailed graphical or statistical analyses could not be run on the rarer species because sample sizes were too small, but a recent die-off appeared to have occurred in all species (Tables 3 and 4) . Although we collected no Lampsilis higginsi in our routine sampling, we found one dead specimen in a sheller's cull pile on a small island near RM 486. It is apparent that if the mortality rates we observed in 1983 and 1985 occur repeatedly and the recruitment is as low as our size distributions indicate (Figure 3) , mussel populations in pools 14 and 15 are in jeopardy. The problem is more extensive than our study indicates — papers presented at the recent workshop on mussel die-off s (Neves 1987) and reports from shellers, district fishery biologists, and other informed observers all indicate that the die-offs of 1983 and 1985 extended over a reach of the Upper Mississippi River several hundred miles long. 19 SUMMARY 1. In 1983, 33.6% of the mussels we collected in pools 14 and 15 of the Mississippi River had died within the year. 2. In 1985, 17.9% of the mussels collected near RM 486.0 and only 6.3% of those near RM 488.6 in Pool 15 had died recently. 3. Mortality rate estimates may have been biased upwards in 1983 because shellers were harvesting only live mussels and leaving dead unsalable shells. In 1985, shellers were able to sell recently dead shells so they probably did not bias mortality estimates . 4. If shelling had no effect on the proportion of recently dead shells, a second hypothesis is that susceptible mussels died in response to some causative agent in 1983 leaving behind only more resistant mussels in 1985. A third hypothesis is that the intensity of some unidentified causative agent was less in 1985 than in 1983. 5. Adults and juveniles of all species were affected in both years. However, mortality rates were significantly greater (P < 0.08) in reproductive adults (31 . 7%-44 . 1%) than in juveniles (17 . 6%-23 . 4%) of Amblema plicata, Quadrula pustulosa, and Megalonaias gigantea, the species for which we had the largest sample sizes. Increased mortality in adults could be associated with the stress of reproduction, or with greater accumulation of some unidentified toxic agent in older individuals. 20 RECOMMENDATIONS 1. Term definitions and techniques to be used in future investigations of mussel die-offs should be standardized to facilitate comparison of different die-off episodes. Terms to categorize the status of shells (live, recently dead, etc.) are defined in this report and may be useful to other investigators. Quantitative sampling using frames and divers should be standard practice, and substrate within sampling frames should be collected and transported to the surface and carefully examined for small specimens . 2. In addition to shell length, age of mussels should be determined by counting annuli if possible so that growth and recruitment rates can be determined. 3 . To determine whether the causative agent for mussel die-offs in the Mississippi River is a transmittable infectious agent, healthy mussels should be exposed to moribund individuals in the laboratory. 4. Body and shell burdens of contaminants should be monitored in healthy mussel populations and in populations where die-offs occur. The effects of any contaminants found in significantly higher concentrations in populations experiencing die-offs should be determined in laboratory bioassays on healthy mussels. 21 5. Mussel sanctuaries should be established to provide unharvested mussel beds where scientists could study mussel ecology without the confounding effects of commercial harvest. The size distributions and recruitment, growth, and mortality rates of relatively undisturbed mussel populations should be determined for comparisons with populations subject to die-offs or harvesting. In addition, these sanctuary beds could serve as seed populations in the future. 22 ACKNOWLEDGMENTS We wish to acknowledge the Illinois Department of Conserva- tion and the National Marine Fisheries Service (U.S. Department of Commerce, NOAA, National Marine Fisheries Service, P.L. 88- 309, project 3-373-R) for financial support for data collection. We received funds for data analysis from Illinois1 Nongame Checkoff program, and we are grateful to the Department of Conservation, the Nongame Advisory Committee, and the taxpayers who checked off a portion of their tax returns for the benefit of nongame species. We are thankful to Bill Fritz (DOC) for providing information from commercial shellers and for his help in the field. We are indebted to DOC biologists Dan Sallee, Butch Atwood, and Bob Schanzle for helping us with the diving. This manuscript was reviewed by Dr. Richard V. Anderson, Kevin S. Cummings, and Bill Fritz; and edited by Jana Waite. The Motorola Mini-Ranger III Radar Ranging System was on loan from the Upper Mississippi River Basin Association. 23 LITERATURE CITED Baker, F.C., 1906. A catalogue of the mollusca of Illinois. Illinois State Laboratory of Natural History Bulletin 7(6) :53-136. Ballenger, D.E., 1986. President, Mississippi Valley Shell Company, Muscatine, IA. Personal communication. 25 June 1986. Ballenger, D.E., 1987. The musseling industry of the Upper Mississippi River and impacts of the recent mussel die-off. Pages 151-153 in R.J. Neves (ed.), Proceedings of the workshop on die-offs of freshwater mussels in the United States, June 23-25, 1986, Davenport, Iowa. U.S. Fish and Wildlife Service and Upper Mississippi River Conservation Committee. 166 p. Blodgett, K.D., and R.E. Sparks, 1987. Documentation of a mussel die-off in pools 14 and 15 of the Upper Mississippi River. Pages 76-88 in R.J. Neves (ed.), Proceedings of the workshop on die-offs of freshwater mussels in the United States, June 23-25, 1986, Davenport, Iowa. U.S. Fish and Wildlife Service and Upper Mississippi River Conservation Committee. 166 p. Calkins, W.W. , 1874. The land and freshwater shells of La Salle County, Illinois. Ottawa Academy of Natural Sciences Proceedings. 48p. Coker, R.E., 1919. Freshwater mussels and mussel industries of the United States. Bulletin of the U.S. Bureau of Fisheries 36:13-89. Separately issued as U.S. Bureau of Fisheries Document Number 8 65. Coon, T.G., J.W. Eckblad, and P.M. Trygstad, 1977. Relative abundance and growth of mussels in pools 8, 9, and 10 of the Mississippi River. Freshwater Biology 7: 279-285. Danglade, E., 1914. The mussel resources of the Illinois River. U.S. Bureau of Fisheries, Appendix 6 to the report of the U.S. Commissioner of Fisheries for 1913. 48p. Duncan, R.E., and P. A. Thiel, 1983. A survey of the mussel densities in Pool 10 of the Upper Mississippi River. Technical Bulletin No. 139. Wisconsin Department of Natural Resources, Madison, WI . 14 p. Finke, A.H., 1966. Report of a mussel survey in pools 4A (Lake Pepin), 5, 6, 7, and 9 of the Mississippi River during 1965. Wisconsin Department of Natural Resources, LaCrossee, WI. 5p. Forbes, S.A., and R.E. Richardson, 1913. Studies on the biology of the upper Illinois River. Illinois State Laboratory of Natural History Bulletin 9 (10) : 481-574 . 24 Fritz, A.W. , 1986. Commercial fisheries biologist, Illinois Department of Conservation, Carlyle, IL. Personal communication. May 1987. Fuller, S.L.H., 1978. Final report: freshwater mussels (Mollusca: Bivalvia: Unionidae) of the Upper Mississippi River: observations at selected sites within the 9-ft channel navigation project on behalf of the United States Army Corps of Engineers. The Academy of Natural Sciences of Philadelphia, PA. 401p. Fuller, S.L.H., 1980. Historical and current distributions of fresh-water mussels (Mollusca: Bivalvia: Unionidae) of the Upper Mississippi River. Pages 72-119 in J.L. Rasmussen (ed.), Proceedings of the UMRCC Symposium on Upper Mississippi River bivalve mollusks. Upper Mississippi River Conservation Committee. Havlik, M.E., 1987. Probable causes and considerations of the naiad mollusk die-off in the Upper Mississippi River. Pages 91-103 in R.J. Neves (ed.), Proceedings of the workshop on die-offs of freshwater mussels in the United States, June 23- 25, 1986, Davenport, Iowa. U.S. Fish and Wildlife Service and Upper Mississippi River Conservation Committee. 166 p. Kelly, H.M. , 1899. A statistical study of the parasites of the Unionidae. Illinois State Laboratory of Natural History Bulletin 5(8) :399-418. Neves, R.J. (ed.), 1987. Proceedings of the workshop on die- offs of freshwater mussels in the United States, June 23-25, 1986, Davenport, Iowa. U.S. Fish and Wildlife Service and Upper Mississippi River Conservation Committee. 166 p. Oblad, B.R., 1979. An experiment in relocating endangered and rare naiad mollusks from a proposed bridge construction site at Sylvan Slough, Mississippi River near Moline, Illinois. Pages 211-222 in J.L. Rasmussen (ed.), Proceedings of the UMRCC Symposium on Upper Mississippi River bivalve mollusks. Upper Mississippi River Conservation Committee. Pratt, W.H. 1876. List of land and freshwater shells found at Davenport, Iowa. Proceedings of the Davenport Academy of Science 1:165-167. Richardson, R.E., 1928. The bottom fauna of the middle Illinois River, 1913-1925. Its distribution, abundance, valuation, and index value in the study of stream pollution. Illinois Natural History Survey Bulletin 17 (12) : 387-475. Sokal, R.R., and F.J. Rohlf, 1969. Biometry. W.H. Freeman and Company, San Francisco, CA. 776 p. 25 Sparks, R.E, and K.D. Blodgett, 1983. Effects of three commercial harvesting methods on mussel beds. Illinois Natural History Survey Aquatic Biology Technical Report 1983 (10) . 44 p. Sparks, R.E., and K.D. Blodgett, 1985. Effects of fleeting on mussels. Illinois Natural History Survey Aquatic Biology Technical Report 1985(8). 94 p. Starrett, W.C., 1971. A survey of the mussels (Unionacea) of the Illinois River, a polluted stream. Illinois Natural History Survey Bulletin 30 (5) : 266-403 . Stein, C.B., 1973. The life history of Amblema plicata, the three-ridge naiad. Ph.D. dissertation, Ohio State University, Columbus, OH. 174 p. Stern, E., 1982. Executive summary of the Higgins1 eye mussel recovery plan. Submitted to the U.S. Fish and Wildlife Service. 17 p. Thiel, P. A. , 1987. Recent events in the mussel mortality problem on the Upper Mississippi River. Pages 66-75 in R.J. Neves (ed.), Proceedings of the workshop on die-offs of freshwater mussels in the United States, June 23-25, 1986, Davenport, Iowa. U.S. Fish and Wildlife Service and Upper Mississippi River Conservation Committee. 166 p. Tryon, G.W. , 1865. Catalogue of mollusca collected by Professor D.S. Sheldon at Davenport, Iowa. American Journal of Conchology 1:68-70. Zale, A. V., and R. Suttles. 1987. Mussel mortalities in the Neosho River System, Oklahoma. Pages 39-43 in R.J. Neves (ed.), Proceedings of the workshop on die-offs of freshwater mussels in the United States, June 23-25, 1986, Davenport, Iowa. U.S. Fish and Wildlife Service and Upper Mississippi River Conservation Committee. 166 p. 26