We simulated populations of threeridge mussels (Amblema plicata, Say, 1817) using empirically derived survival rates. Survival rates were derived from a mark-recapture study of mussels conducted in the Mississippi and Otter Tail rivers, Minnesota. The software package VORTEX was used to develop a base line population model which changed little or not at all through time. Models based on the initial base line data were constructed to simulate behaviors of A. plicata populations under various levels of mortality attributed to zebra mussel (Dreissena polymorpha, Pallas 1771) colonizations. Models were also developed that simulated varying levels of commercial harvesting of A. plicata. Sensitivity analysis revealed that A. plicata populations are most sensitive to alterations in adult survival. Adult survival is the life history stage most often impacted by both D. polymorpha colonizations and commercial harvesting. Population models simulating D. polymorpha mediated mortality revealed that population extinction was likely to occur within 50 y if survival rates remain at the levels recently measured. Models that simulated a commercial harvest of only 5% of the adult A. plicata population predicted that populations will decline by almost 50% in only 40 y. Our recommendation is that a concerted effort should be made to estimate the population size of potentially harvested populations of freshwater mussels. These estimates would allow for a more accurate estimate of what percentage of the adult mussels are actually being harvested. The population estimates would also allow for setting of quotas or limiting the number of permits for harvesters in the face of increased D. polymorpha infestations, thereby ensuring that harvested populations of mussels are not being over exploited. These modeling efforts will be useful for resource managers attempting to establish a sustainable harvest of commercially valuable mussel species which may be competing with a nonindigenous species.
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Vol. 151 • No. 2