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Controlled propagation, augmentation, and reintroduction (PAR) of rare and endangered aquatic organisms has become a priority action for recovery and delisting, and in many cases is an action of “last resort” to either restore or maintain existing populations. The guiding principle of PAR efforts should be to avoid harming existing populations of congeneric or nontarget species and also minimize risks to extant populations and habitats. Controlled PAR of freshwater mussels should not be a long-term management strategy conducted in perpetuity and should not be used as a substitute for recovery tasks such as habitat restoration or addressing the causes of endangerment. The determination to pursue controlled PAR for freshwater mussels should follow a thorough evaluation of the status of existing wild populations, an agreement that PAR in the historic range is needed, and a conclusion that suitable habitat for long-term success is present. The primary purpose of any efforts to augment or reintroduce animals should be to establish free-ranging wild populations. Concomitant with this goal is the distinct possibility that these activities can represent appreciable genetic or ecological risks to resident animals, both nontarget taxa and wild conspecifics. To maintain the integrity of the fauna, communities, and ecosystems it is imperative that these risks be carefully considered before conducting controlled PAR. In this paper we pose several questions that we believe are important to consider before initiating PAR of freshwater mussels. We also recommend actions, some already used at individual facilities or by agencies, that we believe will aid in developing a more uniform approach to controlled PAR and safeguarding the ecological and genetic integrity of freshwater mussel communities.
Mussel monitoring data are abundant, but methods for analyzing long-term trends in these data are often uninformative or have low power to detect changes. We used a dynamic occurrence model, which accounted for imperfect species detection in surveys, to assess changes in species occurrence in a long-term data set (1986–2011) for the Tar River basin of North Carolina, USA. Occurrence of all species decreased steadily over the time period studied. Occurrence in 1986 ranged from 0.19 for Utterbackiaimbecillis to 0.60 for Fusconaia masoni. Occurrence in 2010–2011 ranged from 0.10 for Lampsilisradiata to 0.40 for F. masoni. The maximum difference between occurrence in 1986 and 2011 was a decline of 0.30 for Alasmidonta undulata. Mean persistence for all species was high (0.97, 95% CI = 0.95–0.99); however, mean colonization probability was very low (<0.01, 95% CI = <0.01–0.01). These results indicate that mussels persisted at sites already occupied but that they have not colonized sites where they had not occurred previously. Our findings highlight the importance of modeling approaches that incorporate imperfect detection in estimating species occurrence and revealing temporal trends to inform conservation planning.
Almost half of the mussel species in North America are imperiled, and eight species found in the eastern Gulf Coastal Plain drainages were recently federally listed. Information regarding the status of known populations of these species is either limited or outdated. Three sites in the Choctawhatchee River watershed (southeast Alabama), where federally threatened mussel species were known to occur, were sampled for mussels eight times each over 4 mo. Three federally threatened species, Fusconaia burkei, Hamiota australis, and Pleurobema strodeanum, and one common species, Elliptio pullata, were individually tagged and released using a robust mark-recapture sampling design. Each species-site combination having sufficient sample sizes was analyzed using a set of six candidate mark-recapture models chosen a priori, and estimates of apparent survival, detectability, and density were derived using the computer program MARK to average models. A total of 820 mussels, 427 of which are listed as federally threatened or endangered, were tagged over eight sampling occasions at three sites. Apparent survival of E. pullata varied among sampling occasions (0.96–0.99), while threatened species tended to have nearly constant survival. Detectability increased with mussel length for E. pullata at all sites (0.07–0.82), but with the exception of P. strodeanum at 8M1, length did not affect detectability of threatened species (0.11–0.52). Densities of threatened species (0.05–1.0 individuals/m2) were typically lower than those of E. pullata (0.15–1.78 individuals/m2) at each site. These data offer insights into the current status of known populations of threatened species at three sites in the Choctawhatchee watershed and will serve as a baseline against which the future status of these populations can be measured. These data also demonstrate the potential viability of using these methods for long-term monitoring of these populations.