Using environmental DNA methods to improve detectability in an endangered sturgeon (Acipenser sinensis) monitoring program

Background To determine the presence and abundance of an aquatic species in large waterbodies, especially when populations are at low densities, is highly challenging for conservation biologists. Environmental DNA (eDNA) has the potential to offer a noninvasive and cost-effective method to complement traditional population monitoring, however, eDNA has not been extensively applied to study large migratory species. Chinese sturgeon (Acipenser sinensis), is the largest anadromous migratory fish in the Yangtze River, China, and in recent years its population has dramatically declined and spawning has failed, bringing this species to the brink of extinction. In this study, we aim to test the detectability of eDNA methods to determine the presence and relative abundance of reproductive stock of the species and whether eDNA can be used as a tool to reflect behavioral patterns. Chinese sturgeon eDNA was collected from four sites along the spawning ground across an eight month period, to investigate the temporal and spatial distribution using droplet digital PCR (ddPCR). Results We designed a pair of specific primers for Chinese sturgeon and demonstrated the high sensitivity of ddPCR to detect and quantify the Chinese sturgeon eDNA concentration with the limit of detection 0.17 copies/μl, with Chinese sturgeon eDNA been intermittently detected at all sampling sites. There was a consistent temporal pattern among four of the sampling sites that could reflect the movement characteristics of the Chinese sturgeon in the spawning ground, but without a spatial pattern. The eDNA concentration declined by approximately 2–3 × between December 2018 and December 2019. Conclusions The results prove the efficacy of eDNA for monitoring reproductive stock of the Chinese sturgeon and the e decreased eDNA concentration reflect that Chinese sturgeon may survive with an extremely small number of reproductive stock in the Yangtze River. Accordingly, we suggest future conservation measures should focus on both habitat restoration and matured fish restocking to ensure successful spawning. Overall, this study provides encouraging support for the application of eDNA methods to monitor endangered aquatic species.

Impact and prospects of water conservation on fish habitat and advances of ecobiology operation in Yangtze River, China: A review

Yangtze River, the longest river in Asia, provides 40 percent of freshwater in China and plays an important role in ecological biodiversity. However, this ecosystem has been deteriorated by the continuously construction of reservoirs and hydropower stations. Many investigations have been carried for the biodiversity, hydrological indicators, and species distribution along Yangtze River caused by dam construction. As a result, the ecological operation has been gradually applied to mitigate the negative effects of water conservancy projects. In order to well know recent advances in the study of fish habitat in the Yangtze River Basin, 424 original papers published from 2000 to 2020 using bibliometrics were compiled in this research to analyze the developing trends including topics, data, and research status. The results of literature statistics showed that the related research fields on the effects of the reservoir on hydrological indicators mainly focused on negative impact caused by hydrological changes, water temperature effect, and sediment variation. In the studies on the habitats of fish, the four major Chinese carps and Chinese sturgeon were the main objects of concern, in which multi-objective joint operation, cascade reservoir operation, and model coupling have been widely adapted.

Optimization of the flow conditions in the spawning ground of the Chinese sturgeon (Acipenser sinensis) through Gezhouba Dam generating units

Chinese sturgeon (Acipenser sinensis) is a critically endangered species, and waters downstream from Gezhouba Dam are the only known spawning ground. To optimize the velocity conditions in the spawning ground by controlling the opening mode of Gezhouba Dam generator units, a mathematical model of Chinese sturgeon spawning ground was established in FLOW-3D. The model was evaluated with velocity measurements, and the results were determined to be in good agreement. By inverting the 2016–2019 field monitoring results, the model shows that the preferred velocity range for Chinese sturgeon spawning is 0.6–1.5 m/s. Velocity fields of different opening modes of the generator units were simulated with identical discharge. The suitable-velocity area was maximal when all units of Dajiang Plant of Gezhouba Dam were open. For discharges below 12,000 m3/s, most of the area was suitable; for discharges above 12,000 m3/s, the suitable area rapidly decreased with increasing discharge. A comparison of suitable areas under high-flow showed that at discharges of 12,000–15,000 m3/s, opening 11–13 units on the left side was optimal. For discharges above 15,000 m3/s, all units should be open. We used these results to recommend a new operation scheme to support the conservation of Chinese sturgeon.