Shell Morphometry and Tissue Condition ofAmblema plicata(Say, 1817) from the Upper Mississippi River

Abstract

ABSTRACT We examined shell length-weight relationships and shell shape in the unionid Amblema plicata (Say, 1817) from Pool 10 through Pool 26 of the upper Mississippi River. There were differences in both the intercepts and slopes of the relationships between size and other measured characteristics among the various pools examined. There was a much greater degree of variability in the tissue related factors than in any of the shell factors. There were no apparent upstream-downstream trends in any of the dependent variables. We also found that the shell can contain a significant amount of organic material and the percentage of organic material varied considerably, particularly in larger mussels. This indicates the need to consider the shell in studies of the energy dynamics of unionids. Tissue condition varied with mussel size; larger mussels had proportionally lighter shells and thus higher condition indices than smaller mussels. Because of the significant intra- and inter-pool variability in shell and tissue parameters which we observed, we urge that biomass estimates based on shell length-weight regressions for this and other species should be based on empirical relationships observed for the particular population under study rather than from literature values.