An Evaluation of Streamflow Augmentation as a Short-Term Freshwater Mussel Conservation Strategy

Abstract

Recurrent and prolonged droughts, coupled with increased water resource demand, threaten freshwater mussel populations through stream drying and water quality degradation. Augmentation of stream discharge was proposed as a short-term strategy to maintain adequate streamflows and water quality in reaches with important freshwater mussel populations during exceptionally low flow periods. We investigated the effects of water augmentation on seven freshwater mussel species in a small creek between 2011 and 2014. Using capture-mark-recapture methods, we monitored mussel populations in a control reach upstream of an augmentation outlet and two reaches immediately downstream of an augmentation outlet. Water quality measurements during our study indicated that augmentation improved water temperature and dissolved oxygen conditions during low flow periods. For all mussel species, apparent survival was positively related to minimum streamflows and declined precipitously as streamflows decreased. However, mean apparent survival between sampling occasions was high among all species but did not differ among treatment units, suggesting that flow augmentation rates in this study were insufficient for abating the effects of basin-wide reductions in streamflow. Temporary emigration differed among study reaches but did not support hypothesized relationships because it increased with stream stage and was highest in an augmented reach. This suggests that streamflows did not drop below thresholds, which invoked burrowing as a response to decreased streamflows. Streamflow augmentation may be a viable short-term mussel conservation strategy in small streams but will likely require higher augmentation volume capacity than evaluated during our study. Copyright © 2015 John Wiley & Sons, Ltd.