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.

Estimation of vital population rates to assess the relative health of mussel assemblages in the Upper Mississippi River

“…In many prior mark-recapture studies with freshwater mussels, emigration has been assumed to be temporary and result from vertical migration into the substrate (Meador, Peterson, & Wisniewski, 2011;Villella et al, 2004;Wisniewski, Abbott, & Landis, 2016). However, in WNC, movement from study plots was likely to be permanent and result from mussels being displaced during high flows.…”

“…Creek, GA, U.S.A. (Wisniewski et al, 2016). A 4-year mark-recapture study in the Cacapon River, WV, U.S.A., reported high adult survival rates (> 90%) across three species (Villella et al, 2004).…”

A Comparison of Systematic Quadrat and Capture-Mark-Recapture Sampling Designs for Assessing Freshwater Mussel Populations

“…As it is becoming increasingly important to understand and monitor species-specific population dynamics for conservation management, the incorporation of CMR into mussel monitoring studies has steadily been expanding [25][26][27][29][30][31]71]. Similar to quadrat surveys, CMR is useful for estimating and detecting population trends, but in addition, it can: (1) offer improved precision in population parameter estimates; (2) provide reliable estimates of vital rates (i.e., survival, mortality, recruitment); (3) investigate factors influencing vital rates and detectability; and (4) be used to validate and improve species-specific demographic models-particularly for species occurring at lower densities [10,17,18,26,32].…”

“…Differences in ability to detect individuals among surveyors can be attributed to years of experience, familiarity with target species or the study area, visual acuity, dedication, and mental or physical fatigue [26,27,29]. Although surveyor ability to detect adults at the substrate surface is often positively associated with increasing mussel shell length, CMR studies have demonstrated that this relationship can vary with substrate size and habitat type [26,27,31]. To make things more complex, many of these factors influencing availability and detectability can have interacting effects and vary by species.…”

“…Alternatively, if a study area is relatively small (e.g., <500 m 2 ), a CMR design surveying the entire substrate surface area could easily be implemented in a cost-effective manner. Finally, a Robust Design (integrated closed-and open-population parameter estimators) CMR study is recommended for long-term (≥3 years) monitoring as it allows for estimation of abundance and true survival with improved precision, (temporary) emigration, and recruitment rates-which is crucial to evaluating population viability [2,21,26,27,31,33,83,84]. Overall, CMR approaches are appropriate and feasible for monitoring populations within or across a few study sites.…”