Relations between complex hydraulics and the localized distribution of mussels in three regulated rivers

Abstract

A stratified random sampling design was used to examine the relations between selected hydraulic variables and the density of unionids at five sites on the Green, Licking, and Rough Rivers of Kentucky. We located the strata to ensure that samples occurred in a wide range of hydraulic conditions at each site. Eight 0.25 m2 quadrat samples were collected from each 25 m2 stratum. We measured mean water column velocity, depth, and substrate roughness before we sampled each quadrat. ‘Fliesswasserstammtisch’ (FST) hemispheres were used to estimate shear stress. In all, we collected 798 individuals of 28 species of freshwater mussels. Simple hydraulic characteristics of our study sites were not correlated consistently with mussel density. For instance, water depth and mussel density were positively correlated in the Green River, negatively correlated in the Rough River, and not significantly correlated in the Licking River. In contrast, we found consistent negative correlations in all rivers between mussel density and complex hydraulic variables, such as shear velocity and FST hemisphere number. We believe that the limited recruitment observed in these rivers may have resulted from operation of upstream flood control dams that altered flow regimes seasonally. We suspect that the increased discharge during spring and early summer resulted in shear forces sufficiently high on mussel beds to prevent settlement of newly metamorphosed juveniles. Copyright © 2001 John Wiley & Sons, Ltd.