The extent to which effects seen in chronic toxicity studies in the laboratory affect mussel fitness later in life is poorly known. We examined juvenile Fatmucket (Lampsilis siliquoidea) survival and growth for 56 d following exposure to Zn in a laboratory bioassay. We conducted a 28-d chronic toxicity bioassay with 6-wk-old juvenile mussels exposed to a control and two Zn treatments (120 and 240 µg/L). We then transferred surviving mussels into a grow-out pond and monitored their survival and growth for 56 d. Survival and shell length were lower in both Zn treatments than in the control after the 28-d toxicity bioassay. After the 56-d grow-out period, survival did not differ among treatments, but shell length was lower in the 240-µg/L treatment than in the control and mass was lower in both Zn treatments than in the control. Mussel length was lower throughout the experiment in both Zn treatments than in the control, but there was weak support for a difference in the slopes, suggesting that Zn-exposed mussels may fall farther behind in size over time. Persistence of reduced size following Zn exposure could result in delayed sexual maturation and lowered fecundity, which could have long-term population-level effects.

Conventional survey methods to find rare and endangered aquatic species can be time consuming, expensive, destructive to habitat, and limited by the physical conditions of a site. Sampling for environmental DNA (eDNA) shed by organisms into their environments can overcome these limitations, maximizing conservation resources. However, the optimal spatial sampling interval for eDNA detection is poorly known. We developed and assessed eDNA methods for application to Simpsonaias ambigua (Salamander Mussel), a unionid mussel that is considered at risk throughout most of its range. We developed a quantitative PCR assay and optimized methods to detect S. ambigua eDNA in water samples, and we experimentally determined eDNA shedding and decay rates. We used these rates to populate a previously published eDNA transport model to estimate the maximum downstream distance from the source (i.e., the location of live mussels) at which eDNA could be detected as a function of environmentally relevant source eDNA concentrations and water velocities. The model predicted that maximum detection distance varied greatly depending on source eDNA concentration and water velocity. At low eDNA concentration and water velocity (1.0 copy/mL and ,0.1 m/s, respectively), eDNA will be detected only at the source, requiring spatially intensive eDNA sampling. At higher eDNA concentration and water velocity (5.0 copies/mL and 0.8 m/s, respectively), eDNA can be detected at least 10 km downstream, requiring less intensive sampling. Based on our results, we provide recommendations for the development of optimal eDNA sampling design for detecting rare or endangered species.

Captive propagation followed by release to natural habitats has become a common conservation practice to restore and augment mussel populations, but the genetic effects of these efforts remain poorly studied. We examined genetic variation and genetic structure in 2- to 3-yr-old subadults of Lampsilis cardium and L. siliquoidea that each was propagated from a single broodstock female and subsequently used to augment existing wild populations. We compared genetic variation and structure of the propagated individuals to that of the wild population, including the broodstock females. Using microsatellite markers, we found that propagated subadults retained levels of heterozygosity comparable to the wild population and showed no sign of genetic bottlenecks. This is likely due to high levels of multiple paternity in both species, with the single broodstock females of L. cardium and L. siliquoidea mating with an estimated 13 and 25 sires, respectively. However, propagated subadults had significantly fewer alleles and lower allelic richness and altered allele frequencies compared with wild adults, and genetic structure of propagated individuals was distinct from the wild population. Our results show that propagation from even a single broodstock female can result in offspring that retain most population-level genetic variation. However, the reduced allelic richness and altered genetic structure we observed in propagated individuals underscore the need for future studies to investigate the ecological and evolutionary impacts of propagated individuals on wild populations.

Poyang Lake, China's largest freshwater lake, has high ecological and economic value. The area is a global hotspot of freshwater mussel diversity, and it supports an important dredge fishery for snails, which results in substantial mussel bycatch. The mussel fauna changed dramatically in the last two decades, and many large species disappeared from the lake. We hypothesize that snail dredging may be a factor threatening mussel populations in the area. We describe the snail fishery and its associated mussel bycatch in Qinglan Lake, a satellite of Poyang Lake. We evaluate the potential impact of unselective harvest on the mussel fauna, and we estimate the value of mussels as a commodity for local fishers. Fishers harvested an average of 859 mussels per trip, with 17 mussel species present in the bycatch. We estimated that annual mortality from bycatch represented about 5% of the total mussel standing stock in the lake. The market price for mussels was low compared to target snails. This low value provides a potential conservation opportunity of providing financial incentives to fishers for returning mussels to the lake.