Xin Gao

Immediate impacts of the second impoundment on fish communities in the Three Gorges Reservoir

Long and short term investigations have revealed dramatic changes in fish communities after impoundments by reservoirs. However, the process of these changes during impoundment remains poorly studied. In 2005 and 2006, before and during the second stage of impoundment of the Three Gorges Reservoir (TGR), in the upper reaches of the Yangtze, China, we investigated fish catches to assess the impacts of reservoir filling on fish community structure. We conducted sampling at 2 sites, Wanzhou reach, which had been inundated by the first water filling in 2003, and Fuling reach, which still remained a riverine site before this water filling. The results revealed an evident and immediate shift of fish communities from lotic to lentic components. In the Wanzhou reach, during the filling, the abundance percentage of lentic fish increased to 94% compared to 69% before the filling. In the Fuling reach, after the filling, lotic fish declined in abundance from 99% to 85%, while lentic fish increased from less than 1% to 12% in abundance. Based on our investigation and the regulation scheme of the TGR, we predicted that after the completion of the Three Gorges Dam (TGD), there would be typical lacustrine, transitional and riverine zones in TGR, with their corresponding fish assemblages. We suggest that long term monitoring should be conducted to evaluate the future ecological effects, and different strategies implemented in these three zones for conservation purposes.

Effects of damming on population sustainability of Chinese sturgeon, Acipenser sinensis : evaluation of optimal conservation measures

The numbers of spawning sites for Chinese sturgeon have been drastically reduced since the construction of the Gezhouba Dam across the Yangtze River. This dam has blocked migration of Chinese sturgeon to their historic spawning ground causing a significant decline of the Chinese sturgeon population. We conducted a VORTEX population viability analysis to estimate the sustainability of the population and to quantify the efficiency of current and alternative conservation procedures. The model predicted the observed decline of Chinese sturgeon, resulting from the effect of the Gezhouba Dam. These simulations demonstrated the potential interest of two conservation measures: increasing spawning area and reducing predation on sturgeon eggs. The simulations also demonstrated that the actual restocking program is not sufficient to sustain sturgeon population as the artificial reproduction program induce the loss of more wild mature adults that the recruitment expected by the artificial reproduction.

Interannual variations of the fish assemblage in the transitional zone of the Three Gorges Reservoir: persistence and stability

The construction of dams may lead to dramatic changes in fish assemblages due to the loss of lotic habitat caused by impoundment, which have been well documented. However, knowledge of the temporal variation of fish assemblages in the transitional zone, which is an ecotone between lotic and lentic environments of the reservoir, is still very rare. In the present study, fishes in the transitional zone of the Three Gorges Reservoir were sampled from 1997 to 2002 and from 2006 to 2009 to investigate interannual variations of fish assemblages. The results showed that 9 families, composed of 77 species, were found in the transitional zone with Cyprinidae as the dominant group. By cluster analysis (CLUSTER) and non-metric multidimensional scaling analysis (MDS), assemblages were separated into two groups at a Bray-Curtis similarity value of 77.26%, representing the pre-impoundment period and post-impoundment period. Following analysis of similarity percentages of species contributions (SIMPER), shifts in abundances of Coreius guichenoti, Rhinogobio cylindricus and Coreius heterodon, etc. contributed most to the difference between the two groups. Surprisingly, contrasting to the drastic changes in lacustrine region, the fish assemblage in the transitional zone appeared to be relatively stable, since the ten core species caught were consistently recorded every year, and no significant species replacement occurred during our study period. Besides, the moderate index of persistence indicated persistence of the fish assemblage as well, in spite of the shift of some species. Based on the results of ordination and time-lag analysis, the fish assemblage in the transitional zone showed no directional change. We conclude that fish assemblage in the transitional zone of the Three Gorges Reservoir was stable across the surveyed years. Based on our results, we propose that maintenance of dynamic transitional zones in reservoirs will be useful for the preservation of fishes, particularly for the endemic species inhabiting the upper Yangtze.

Extinction risk and conservation priority analyses for 64 endemic fishes in the Upper Yangtze River, China

It is a global concern to assess extinction risk and set conservation priority for threatened species. In the present study, we assessed extinction risks and conservation priorities for 64 endemic fish species in the Upper Yangtze River, which might be threatened by cascade dams in the Lower Jinsha River. Eight independent criteria were selected and scored to calculate an Extinction Risk Index (ERI) and a Conservation Priority Index (CPI) for each species with a linear rating system. These criteria reflect extinction-prone life-history traits, distribution characteristics, threat extents, and other conservation concerns. Species with high current threats, large body sizes, low fecundity, low historical occurrences and low recent-record rates had high ERIs (i.e. high risk of extinction). High CPIs (i.e. high conservation priorities) were assigned to species (e.g. Yangtze sturgeon) that represented those most in need of conservation in the impacted region given their high extinction risks, high levels of future threat from damming, high economic and genetic values. We recommend habitat protection and other conservation measures should be taken to conserve those endemic fish species with high conservation priorities.

Effects of water temperature and discharge on natural reproduction time of the Chinese sturgeon, Acipenser sinensis, in the Yangtze River, China and impacts of the impoundment of the Three Gorges Reservoir.

Chinese sturgeon, Acipenser sinensis, is a critically endangered anadromous fish species spawning in the Yangtze River of China during October and November. In this study, we analyzed the effects of hydrological factors, such as water temperature and discharge, on the natural reproduction time of the Chinese sturgeon and evaluated the impact of the impoundment of the Three Gorges Reservoir (TGR) based on our survey data from 1998 to 2011. The results showed that the first spawning dates were significantly (P < 0.05) correlated with the date of water temperature reaching 20°C (20°C WT dates), October mean discharge (Oct. discharge), and the discharge change from October to November (Oct—Nov &Dgr;discharge). Regression analysis suggested that oneday delay of 20°C WT dates could postpone the first spawning date by 0.673 days. A discharge increase of 1000 m3s-1 in October could bring forward the first spawning date by two days. Our results also indicated that the impoundment of the TGR had delayed the first spawning time due to water temperature lag and flow regulation. We suggest the following ecological regulations in order to facilitate conservation of the Chinese sturgeon: to eliminate water temperature lag by regulating water temperature downstream of the Three Gorges Dam (TGD), to enhance water discharge downstream in October, and to complete impoundment before October.

Effects of Environmental Factors on Natural Reproduction of the Four Major Chinese Carps in the Yangtze River, China

The four major Chinese carps are commercially important fish species with high production in China. However, their recruitment decreased sharply in the Yangtze River since the late 20th century. In the present study, to reveal the relationships between spawning activities of the four species and environmental factors, drifting eggs were collected at Yidu City, in the middle reaches of the Yangtze River, from May to July each year between 2005 and 2010. Classification and regression trees (CART) analysis was applied to identify the key factors associated with spawning activities of the four carp species. Twelve predictor variables (hydrological and meteorological variables) and one response variable (egg presence or number of egg) were included in the CART. Our CART analysis showed that water temperature and the diurnal increase of water level were the two most significant factors for the spawning activities. When water temperature was between 18°C and 24°C, especially in association with the diurnal increase of water level greater than 0.55 m·d-1, spawning activities was always favored. Unlike the hydrological factors, meteorological factors seemed to have no influence on initiating the spawning activities. The density of drifting eggs of the four species was mainly influenced by the diurnal variation of water level, the diurnal variation of water discharge, water temperature, humidity, and air pressure. We then related our results to the ecological regulation of the Three Gorge Reservoir in the middle reaches of the Yangtze River. We suggested that, when water temperature was between 18–24°C from May to July, to ensure the successful spawning of the four carp species, the ecological regulation should be managed to create flood peaks and make the diurnal increase of water level greater than 0.55 m·d-1.

Impact of the Three Gorges Dam on the spawning stock and natural reproduction of Chinese sturgeon in the Changjiang River, China

Chinese sturgeon (Acipenser sinensis) is the flagship species of the Changjiang River. The migration route of this species is blocked by the first dam, the Gezhou Dam, and its reproduction is affected by the Three Gorges Dam (TGD), one of the largest dams in the world. We studied the impact of the impoundment of the Three Gorges Reservoir (TGR) since 2003 on the spawning stock and the natural reproduction of the Chinese sturgeon by using our monitoring data from 1997 to 2013. Results indicate that TGR impoundment has delayed the first spawning dates of the fish from middle-late October to late November, decreased the amount of spawning activities from twice to only once each year, and significantly reduced egg production. In particular, the fish did not demonstrate any spawning activities in 2013. Therefore, TGR impoundment significantly affects the natural reproduction of the fish downstream of the TGD. The spawning stock size of the fish is also predicted to further decrease in the future, which will lead to a risk of population extinction. Ecological regulations must be imposed on decreasing the water temperature to 20°C before mid-October and increasing water discharge downstream of the TGD in October to induce spawning of the Chinese sturgeon.

Threatened fishes of the world: Acipenser dabryanus Duméril, 1869

[Gao, Xin; Wang, Jian Wei] Chinese Acad Sci, Inst Hydrobiol, Wuhan 430072, Hubei Province, Peoples R China; [Brosse, Sebastien] Univ Toulouse 3, CNRS, UMR 5174, Lab Evolut & Diversite Biol, F-31062 Toulouse 4, France

Life tables and elasticity analyses of Yangtze River fish species with implications for conservation and management

In conservation biology, knowing the life history strategy of a species is crucial for deciding which stage needs the greatest protection: reproduction, juveniles, or adults. Here, we compiled biological data for 83 Yangtze River fish species, constructed their life tables and conducted elasticity analyses, which calculates the proportional contribution of each vital rate (age-specific survival and fecundity) to the annual population multiplication rate. Life tables showed that, for our analyzed species, the survival rate of age 0 fish was extremely low, ranging from 1.25xa0×xa010−6 to 1.74xa0×xa010−2xa0year−1. All species showed a type III survivorship curve. Elasticity analysis revealed slow–fast continuum life histories ranging from species with a high contribution of fertility elasticity to the population growth rate, but lower juvenile and adult survival elasticity, as well as early maturation and short generation time to species that mature late, possess a long generation time, exhibit low fertility elasticity, and a high adult or juvenile survival elasticity. In addition, the analysis of all the species showed that fertility elasticity was significantly smaller than the sum of juvenile and adult survival elasticity, indicating the need to increase the juvenile and adult survival rates of Yangtze fish rather than focusing only on protecting reproduction and age 0 survival via a breeding season fishing ban which is the current conservation practice. Since overfishing has been proposed as the major factor responsible for the decline of Yangtze fish populations, we further suggest that controlling fishing pressure on juvenile and adult fish is another key conservation requirement.

Impact of the Three Gorges Dam on reproduction of four major Chinese carps species in the middle reaches of the Changjiang River

Silver carp (Hypophthalmichthys molitrix), bighead carp (Aristichthys nobilis), grass carp (Ctenopharyngodon idella), and black carp (Mylopharyngodon piceus) are the four major Chinese carps and are commercially important aquaculture species in China. Reproduction of these carp has declined since the construction of the Three Gorges Dam (TGD) due to an altered water flow and thermal regime in the Changjiang (Yangtze) River. However, details of the changes in reproduction of the four species are not well understood. To assess the impact of the TGD on reproduction of the four carp, we investigated their eggs and larvae at Yidu City, which is 80 km below the TGD, during 2005–2012. We examined diff erences in larval abundance of the four species in the Jianli section (350 km downstream of the TGD) before (1997–2002) and after (2003–2012) construction of the TGD. Based on these observations, the first spawning date of the four species was delayed a mean of about 25 days after the dam was constructed. Mean egg abundance in the Yidu section of the river was 249 million and mean larval abundance was 464 million, which were significant decreases since the 1980s. Moreover, larval abundance in the Jianli section after the dam was constructed was significantly lower than that before construction (ANCOVA, P<0.05). The observed larval abundance accounted for only 24.66% of the predicted value in 2003 when the dam was first inundated. The present spawning grounds between the TGD and Yidu section of the river are very similar to those described in the 1980s, and some spawning grounds exist upstream of the TGD. Large free-flowing stretches upstream of the TGD and the creation of artificially flooded downstream reaches are needed to stimulate spawning and eff ectively conserve these four major Chinese carps species.