Variation in the suitability of Chinese sturgeon spawning habitat after construction of dams on the Yangtze River

The Chinese sturgeon (Acipenser sinensis) is an anadromous fish inhabiting the Yangtze River. Migration of Chinese sturgeon from the estuary to upper Yangtze River was blocked by Gezhou Dam, completed in 1981, and a new, much smaller, spawning ground was established below the dam. However, Three Gorges Dam began operating in 2003, altering hydrological conditions in the new spawning grounds and the impact on Chinese sturgeon reproduction was severe. The annual survey of Chinese sturgeon shows that both spawning scale and breeding population decreased during this period. To illustrate the impact of Three Gorges Dam on the spawning grounds and reproduction of Chinese sturgeon, the habitat suitability of spawning grounds on spawning day was simulated using River2D. Results show that the area of suitable spawning grounds positively correlates with the scale of reproduction and both have decreased sharply since 2003.     

Migrations and movements of adult Chinese sturgeon Acipenser sinensis in the Yangtze River, China

From 2006 to 2009, 27 ultrasonic-tagged wild adult Chinese sturgeon Acipenser sinensis [eight males, 19 females; total length (L(T)) range = 245-368 cm] were captured on the spawning ground just downstream of Gezhouba Dam (GZD) in the Yangtze River. Twenty-six individuals were tracked for 7 to 707 days (mean number of relocations = 859; range = 3-4549). Acipenser sinensis movements were divided into four categories: (1) spawning migration, two tagged A. sinensis (one female and one male) returned to the Yangtze River and migrated from the Yangtze Estuary (river kilometer, rkm, 0) to the spawning ground (1678 rkm) between June and October. Their mean upstream ground speed was 1.41 km h(-1) (range = 0.26-2.35 km h(-1) ). The speed of the male was faster than the female; (2) pre-spawning holding, four of five females tagged in November 2008 stayed within 1678.00-1674.15 rkm for c. 1 year before the spawning period; (3) spawning movements, all A. sinensis swam mostly from the tailrace of the GZD (1678 rkm) to the Miaozui (1674.15 rkm) reach and some moved downstream c. 18.21 rkm (range = 3.93-24.64 rkm), but then, returned upstream to the GZD. Most tagged A. sinensis were on the spawning ground on the day when the spawning occurred; (4) post-spawning migration males (n = 6) and females (n = 2) departed the spawning area on a different time schedule, females leaving before males. The mean seaward ground speed of six A. sinensis was 4.87 km h(-1) (range = 0.68-7.60 km h(-1) ). There were no significant differences (P > 0.05) in ground speeds among reaches or between sexes within reaches between telemetry receivers. These broad spatiotemporal scale results will help establish an effective protection strategy for the species in the Yangtze River.     

Potential causes of habitat degradation and spawning time delay of the Chinese sturgeon (Acipenser sinensis)

In fish conservation, it is important to simulate fish habitat suitability and determine the potential impact on habitat quality and species behavior. This study analyzed the impact of several hydraulic projects on fish habitat quality and spawning time by numerical modeling. The case study involved the only Chinese sturgeon spawning site in the Yangtze River, China. Four habitat assessment indexes reflected both habitat quality and spatial characteristics, including fragmentation and connectivity. Previous studies did not simulate the water temperature impact on the fish habitat; spawning time delay was attributed to water temperature increases and discharge decreases. The results of the present study showed that the water temperature increase from the Three Gorges Reservoir (TGR) impoundment primarily caused the habitat degradation and spawning time delay. The effect of the water temperature increase on the degradation of average habitat suitability was eight times that of a decrease in discharge. A 25-day delay in the water temperature trend line was significantly correlated with a 26-day delay in the first spawning date. A decrease in discharge after TGR impoundment did not cause the spawning date delay. The Dike Project mainly impacted spawning site connectivity. Controlling the water temperature of the released water discharge is the most important means of conserving the wild Chinese sturgeon. This research can benefit other regions considering hydraulic projects by identifying potential factors impacting fish habitat quality and overall ecosystem health.     

Using drift nets to capture early life stages and monitor spawning of the Yangtze River Chinese sturgeon (Acipenser sinensis)

A sampling system for capturing sturgeon eggs using a D-shaped bottom anchored drift net was used to capture early life stages (ELS) of Chinese sturgeon, Acipenser sinensis , and monitor annual spawning success at Yichang on the Yangtze River, 1996–2004, before and just after the Three Gorges Dam began operation. Captured were 96 875 ELS (early life stages: eggs, yolk-sac larvae = eleuthero embryos, and larvae); most were eggs and only 2477 were yolk-sac larvae. Most ELS were captured in the main river channel and inside the bend at the Yichang spawning reach. Yolk-sac larvae were captured for a maximum of 3 days after hatching began, indicating quick dispersal downstream. The back-calculated day of egg fertilization over the eight years indicated a maximum spawning window of 23 days (20 October–10 November). Spawning in all years was restricted temporally, occurred mostly at night and during one or two spawning periods, each lasting several days. The brief temporal spawning window may reduce egg predation by opportunistic predators by flooding the river bottom with millions of eggs. During 1996–2002, the percentage of fertilized eggs in an annual 20-egg sample was between 63.5 to 94.1%; however, in 2003 the percentage fertilized was only 23.8%. This sudden decline may be related to the altered environmental conditions at Yichang caused by operation of the Three Gorges Dam. Further studies are needed to monitor spawning and changes in egg fertilization in this threatened population.     

Assessing the effect of Separation Levee Project on Chinese sturgeon (<Emphasis Type="Italic">Acipensor sinensis</Emphasis>) spawning habitat suitability in Yangtze River,China

Chinese sturgeon (Acipenser sinensis) is a protected anadromous fish species. The migration pattern of the fish has been blocked by the construction of Gezhouba Dam, reducing the natural spawning site length to less than 7 km along the Yangtze River. However, the fish has since established an alternative spawning ground in the narrow reach downstream of Gezhouba Dam. To enhance navigation, a Separation Levee Project (SLP) was implemented in the new-found spawning habitat of the fish. To therefore evaluate the effect of the SLP on Chinese sturgeon spawning habitat suitability, the conditions in the spawning habitat were simulated using River2D (a two-dimensional hydrodynamic model). Two main approaches (habitat kinetic energy and circulation metrics) were used in the simulation. The study showed that SLP only slightly changed the physical conditions in the spawning habitat. Using hydrodynamic simulation, the weighted usable area (WUA) before and after the SLP construction was also computed and habitat preference curve developed for water depth and velocity. On the average, SLP reduced WUA—a finding that was consistent with field-measured data. Based on WUA, the habitat conditions were more sensitive to SLP proximity than metrics based on velocity gradients. SLP posed detrimental impacts on the suitability of spawning habitats of Chinese sturgeon. The findings in this study provide further basis for the protection and restoration of Chinese sturgeon spawning habitats in especially the lower reach of Yangtze River.     

Using adaptive resolution imaging sonar to investigate Chinese sturgeon (Acipenser sinensis Gray, 1835) behaviour on its only spawning ground in the Yangtze River

The present study investigated the presence of Chinese sturgeon Acipenser sinensis on its only remaining spawning ground (below the Gezhauba Dam), and monitored the behaviour under different environmental conditions from 24 December 2015 to 23 January 2016. A fixed ARIS (Adaptive Resolution Imaging Sonar) system was used and a total of 72 Chinese sturgeon were detected during nine observations. Detections initially recorded a few A. sinensis in the early days of late‐December 2015, with an increase in recordings, leading to a peak in early‐January 2016 and declining thereafter. Water temperature slowly decreased during the study period from 18.1 to 15.7°C. During the middle of this temperature decline the sturgeon observations peaked, suggesting that Chinese sturgeon could have an optimal temperature range. The sturgeon Detections Per Unit Effort (DPUE) was higher in the night hours, peaking before dawn, suggesting a circadian behaviour rhythm. Sturgeon spawning was not observed during the investigation period. A delay in the decrease in water temperature caused by the Three Gorges Reservoir and the few numbers of reproductively mature individuals are suspected to have contributed to the failure in natural breeding.     

长江口中华鲟幼鱼对底质的选择

采用单因子实验方法,研究了中华鲟幼鱼对沙(直径＜0.2 cm)、小砾石(直径1～2 cm)、中砾石(直径4～5 cm)、大砾石(直径13～15 cm)4种底质类型的选择.结果表明:单尾鱼实验时,中华鲟幼鱼(体长283.0 mm±18.6 mm,体质量86.2 g±17.8 g,n=30)在4种底质中的时间百分比分别为沙51.50%±21.20%、小砾石20.27%±9.70%、中砾石18.03%±6.17%、大砾石10.20%±11.20%,幼鱼在沙底质中时间明显长于其它3种底质,且差异极显著(P＜0.01);多尾鱼实验时,中华鲟幼鱼(体长278.0 mm±14.3 mm,体质量79.2 g±19.6 g,n=30)在4种底质中的数量百分比分别为沙46.25%±8.06%、小砾石19.38%±7.72%、中砾石18.75%±7.19%、大砾石15.63%±8.92%,幼鱼在沙质底质中的数量明显高于其它3种底质,且差异极显著(P＜0.01);多尾鱼实验中,活动鱼(在水层中游动,不贴底)在4种底质中的数量无显著差异(P＞0.05);非活动鱼(贴底游动或静止)在沙底质中的数量显著高于其它3种底质(P＜0.01).单尾鱼(从时间角度)和多尾鱼(从数量角度)实验均表明,中华鲟幼鱼明显选择沙底质.     

Environmental cues for natural reproduction of the Chinese sturgeon,Acipenser sinensis Gray, 1835, in the Yangtze River,China

For effective conservation, it is important to explore the environmental cues initiating the spawning activities of a fish species. Based on monitoring data gathered between 1998 and 2011, the relationships between spawning activities of the Chinese sturgeon, Acipenser sinensis, and several environmental cues were analyzed using the rare events logistic regression ‘Relogit’ method, which indicated that water temperature, 1‐day ?‐discharge, and atmospheric pressure were among the key spawning cues for A. sinensis (P < 0.05). It is suggested that Chinese sturgeon might have an optimal environment window of 17–20°C water temperature, high day‐to‐day discharge increase, and low atmospheric pressure for spawning. In support of Chinese sturgeon reproduction, suggested modifications to the operational procedures for the Three Gorges Reservoir (TGR) to trigger spawning are: lowering the downstream water temperature to below 20°C before mid‐October and expanding the period with water temperatures of between 17 and 20°C; to create a day‐to‐day intermittent increase in the discharge to an optimal spawning water temperature; and to regulate flow at nights with a low atmospheric pressure.     

The skull of the Chinese sturgeon,Acipenser sinensis (Acipenseridae)

The Chinese sturgeon, Acipenser sinensis, is a large member of Acipenseridae now found only in the Yangtze River and the Yellow and East China seas. The goal of this paper was to describe the skull of A. sinensis in the context of recent anatomical and systematic studies of sturgeons. Five specimens (354–670 mm standard length) were prepared as skeletons. The left and right parietals and frontals are broadly separated by a median fontanelle. The lateral‐most lateral extrascapular variably supports the confluence of the supratemporal, occipital and trunk lateral lines. There is no distinct ventral supraorbital process as found in other sturgeons. The anterodorsal portion of the snout is unique among Acipenseridae by having a single large anamestic dorsal rostral bone instead of a series of separate dorsal rostral bones. There are 0–2 lateral rostral bones on each side positioned anterior to but not in contact with the horizontal arm of the jugal. The dorsal surface of the neurocranium lacks a pineal opening, and its anterior tip is sharply pointed in the smaller specimens examined and gently curved in larger specimens. The anteromedial arm of the palatopterygoid is broad relative to other acipenserids. These new morphological data are discussed and compared among Acipenseridae.     

Growth and feeding ecology of juvenile Chinese sturgeon,Acipenser sinensis,in the Yangtze Estuary

The present study was conducted to assess growth and the feeding ecology with prey preferences of juvenile Acipenser sinensis individuals in the Yangtze Estuary from May to August, 2015. From May to August, juveniles grew from 11.65 ± 2.10 cm (10.82 ± 6.32 g) to 27.78 ± 3.36 cm (158.08 ± 60.50 g), and the length‐weight relationship (b = 3.1124) indicated isometric growth. The stomach content analysis indicated the following order of dominance of prey groups: fish, crab, amphipoda, polychaeta, shrimp and other small benthic invertebrates. The main diet taxon has not changed dramatically compared with samples in 2004. Moreover, this study confirmed that changes occurred in the prey composition, which was different with the growth of length size in the Yangtze Estuary. Therefore maintaining species richness in the Yangtze Estuary and ensuring sufficient food source is crucial to species conservation of A. sinensis.     

三峡库区支流生境因子对库区蓄水的响应

三峡水库的运行调度,使库区支流形成了截然不同的3种河段类型:完全受水库蓄水影响的145m回水段(完全河段),既受蓄水影响又受自然洪汛影响的145—175m回水段(双重河段)以及不受蓄水影响的大于175m的自然河流段(自然河段)。为明确库区蓄水对河流不同河段生境因子的影响程度及差异,对三峡库区36条重要支流的254个河段进行河流生境调查,进行不同河段下生境指标的因子分析,并进一步分析水文情势自然性与不同河段各生境因子的相关关系。结果表明,植被状况对3种不同河段来说均为重要生境因子,但受三峡水库蓄水影响,完全河段植被结构不完整;受库区蓄水影响,完全河段与双重河段及自然河段相比,流速流态状况、表层覆盖物状况、河岸带宽度、湿润率等生境因子有明显改变;水文情势自然性对不同河段生境因子的影响不同。     

Microsatellites assessment of Chinese sturgeon (Acipenser sinensis Gray) genetic variability

Four microsatellites were used to examine the genetic variability of the spawning stocks of Chinese sturgeon, Acipenser sinensis, from the Yangtze River sampled over a 3‐year period (1999–2001). Within 60 individuals, a total of 28 alleles were detected over four polymorphic microsatellite loci. The number of alleles per locus ranged from 4 to 15, with an average allele number of 7. The number of genotypes per locus ranged from 6 to 41. The genetic diversity of four microsatellite loci varied from 0.34 to 0.67, with an average value of 0.54. For the four microsatellite loci, the deviation from the Hardy–Weinberg equilibrium was mainly due to null alleles. The mean number of alleles per locus and the mean heterozygosity were lower than the average values known for anadromous fishes. Fish were clustered according to their microsatellite characteristics using an unsupervised ‘Artificial Neural Networks’ method entitled ‘Self‐organizing Map’. The results revealed no significant genetic differentiation considering genetic distance among samples collected during different years. Lack of heterogeneity among different annual groups of spawning stocks was explained by the complex age structure (from 8 to 27 years for males and 12 to 35 years for females) of Chinese sturgeon, leading to formulate an hypothesis about the maintenance of genetic diversity and stability in long‐lived animals.