Effects of reservoir management on abundance, condition, parasitism and reproductive traits of downstream mussels

The large‐scale impoundment of rivers has led to global declines in freshwater mussel populations. It is important to understand the mechanisms underlying these declines to initiate an effective recovery strategy. We examined population traits of three Quadrula species ( Quadrula pustulosa , Q. cylindrica and Q. quadrula ) at three locations that were exposed to two different reservoir management regimes: releases that mimicked natural flow patterns and releases that were higher and colder in summer months than the natural system. We found lower mussel density, higher hermaphroditism and parasitism rates, and reduced body condition downstream of the dam with unnatural flow regimes. Sex ratios varied on a species and site basis. We found more Quadrula cylindrica females than males averaged across all three sampling sites while Q. pustulosa was male biased across all sites and at site 1. We observed approximately equal sex ratios in Quadrula quadrula . Population disturbances downstream of the more naturally‐regulated dam were not as severe. Our data indicate that dam operation can have effects on a variety of mussel life history characteristics that may ultimately reduce population viability.