unionid mortality (> 90%) occurs when zebra mussel 

 densities and mean infestation intensity reach 6,000/m- 

 and 100/unionid. We predict that by 1996 or 1997 

 unionid mussels in Reach 15 of the UMR will experience 

 significantly greater infestations by zebra mussels and will 

 subsequently suffer reduced fitness and increased 

 mortality. 



Management Recommendations 



A primary objective of this comprehensive study 

 was to provide resource managers with critical 

 information necessary for the evaluation of management 

 and conservation strategies to protect, preserve, or 

 enhance freshwater mussels in the Upper Mississippi 

 River. 



Analysis of quantitative data collected on mussel 

 populations in Reach 15 of the UMR over the past decade 

 shows that mussel populations have declined significantly, 

 recruitment of many species is sporadic, mortality has 

 been relatively high, growth rates are generally slow, 

 illegal harvest has occurred in the mussel refuge, and 

 zebra mussel abundance and infestation of unionids are 

 increasing rapidly. We believe the following management 

 actions could help to conserve mussel populations in 

 Reach 15 and possibly throughout the entire UMR. 



(1) Close the commercial harvest of live Megalonaias 

 nervosa (Washboard). Studies conducted by the INHS 

 in Reach 15 since 1983 indicate M. nervosa populations 

 have suffered a significant (p < 0.001) decline in mean 

 density (Table A-9), most likely the result of extensive 

 commercial exploitation, unexplained die-offs from 1982 

 to 1985, and only one substantial recruitment event in the 

 past ten years (Figure F-3). 



Commercial harvest reports from Illinois 

 (Williamson 1994) and Iowa (Ackerman 1996) indicate a 

 significant decline in the reported catch of live washboard 

 despite a significant increase in fishing effort. In the 

 Illinois portion of the Mississippi River 1 ,092,330 pounds 

 of live washboard were reportedly harvested in 1987, 

 compared to 49,967 pounds in 1994. In the Iowa portion 

 of the Mississippi, 296,988 pounds of live washboard 

 were harvested in 1986, compared with only 1254 pounds 

 in 1992. In the past eight years the average price paid for 

 live washboards has increased nearly 1000%, increasing 

 from $0.22/lb in 1987 to $2.40/lb in 1995. As the 

 number of live washboards has decreased, buyers have 

 turned to dead (relic) washboards to meet the increasing 

 demand of their Japanese consumers. In 1995 the average 

 price paid for relic shell was $1.40/lb. 



In the late 1980's, Fritz (1988) recommended a 

 larger minimum harvest size or a ban on the harvest of 

 washboard in some reaches of the Mississippi River as the 

 only alternatives to prevent the serious stock depletion of 

 this species. Commercial harvest reports from 1987 to 

 1995 and results from the present mussel survey of Reach 

 15 indicate washboard stocks may be at or below the 

 critical level required to maintain themselves, even 

 without additional commercial pressure. At this point, 

 merely increasing the size restrictions is an unacceptable 

 alternative, as it would still allow the further depletion of 

 the reproductive stock. If commercial harvest of live 

 washboard is allowed to continue unchecked, they may 

 soon be extirpated from some reaches of the UMR. 



(2) Establish entire reaches as mussel refuges. 



Although we support the need and rationale for mussel 

 refuges, we believe the current mussel refuges only exist 

 on paper and subsequently do not provide the services for 

 which they were intended. Our studies in Reach 15 

 suggest illegal harvest has occurred in the Sylvan Slough 

 refuge, since all commercial species collected within the 

 refuge demonstrate a truncated size distribution at the 

 minimum commercial size limit (Appendix D), a 

 characteristic of harvested areas. In fact, individuals have 

 been prosecuted for harvesting mussels in Sylvan Slough 

 and other UMR mussel refuges (Scott Wright, IDNR 

 Conservation Warden, personal communication). 

 According to Wright, enforcement is difficult in that 

 shellers must be caught harvesting within the refuge 

 boundaries. Once removed from the refuge, illegally 

 harvested shells can not be distinguished from legal shells 

 taken elsewhere. If an entire reach were designated as a 

 refuge, any persons possessing shells on the water or at 

 access sites (boat ramps) within the designated reach 

 would be subject to prosecution. 



The Upper Mississippi River Conservation 

 Committee's (UMRCC) mussel ad hoc committee, which 

 is composed of representatives from the five UMR states, 

 recently recommended that two entire reaches of the 

 Mississippi River be set aside as mussel refuges. An 

 ideal reach for designation as a refuge would have the 

 following characteristics: (1) good baseline data (mussel 

 recruitment, density, diversity, harvest, etc.), (2) high 

 density of commercial and non-commercial species, (3) 

 high species diversity, (4) presence of threatened, 

 endangered, or special concern species, and (5) conducive 

 to enforcement (limited access, law enforcement presence, 

 and public support). We believe Reach 15 has all these 

 characteristics and would be a good candidate for a 

 mussel refuge. 



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