三峡库区涪陵江段产漂流性卵鱼类的早期资源及其对水文和水温特征的响应

三峡水库调度运行改变了库区江段的水文情势,影响漂流性卵苗在库区江段内的时空分布特征。在水库低水位运行时,具有流水生境特征的库中和库尾江段是产漂流性卵鱼类在整个三峡库区内重要的产卵江段。了解三峡库中和库尾江段产漂流性卵鱼类的早期资源状况及其对水文和水温特征的响应关系,对于采取适宜的保护措施促进鱼类早期资源的恢复具有重要的意义。本文通过2017—2020年5—7月在库中涪陵断面进行的逐日早期资源监测,了解三峡库中和库尾江段产漂流性卵鱼类早期资源的种类组成、产卵规模、产卵场分布及其年际变动特征,并采用随机森林(RF)模型,分析鱼类逐日产卵规模变动与水文、水温格局及其过程的关系,辨识影响不同种类产卵规模变动的关键水文及水温要素。结果表明:2017—2020年共采集到漂流性鱼卵21种,包括长江上游特有鱼类鱼卵3种;以圆筒吻鮈Rhinagobio cylindricus、蒙古鲌Chanodichthys mongolicus、贝氏(?)Hemiculter bleekeri等6种鱼类的鱼卵为主,占总采集鱼卵数的88.76%;各年的鱼卵规模分别为83.04×10⁸、14.29×...

Fish resources of the early life history stages in the Fuling section of the Three Gorges Reservoir and their responses to hydrological and thermal characteristics

Reservoir operation resulting from river damming has altered the flow regimes of the river sections of reservoirs, inducing profound impacts on the spatiotemporal distribution of the early resources of fish species that spawn drifting eggs (FSDE) in the river sections of reservoirs. During the period of low water-level operation stage of the reservoir, the river section with flowing-water habitats is an important spawning river section compared those other sections of the reservoir. Fully understanding the status of early resource of FSDE and their response to hydrological and thermal characteristics in a reservoir''s middle and tail reaches is of great significance for the restoration and promotion the scale of early resource. This paper intended to reveal the inter-annual variation in the species composition of eggs and larvae collected, as well as the spawning scale and distribution of fish spawning grounds in the middle and tail reaches of the Three Gorges Reservoir (TGR), through the daily sampling for eggs and larvae being conducted at the Fuling section from May to July in 2017-2020. The random forest model was further performed to clarify the relationships between the variations in the daily spawning scales and the hydrological, thermal patterns and process conditions, aiming to identify the key hydrological and thermal factors affecting the variations of spawning scales of different species. The results showed that: 1) 21 species of eggs were collected, including 3 species of fish eggs that endemic to the upper reaches of the Yangtze River, and the amounts of eggs of 6 fish species, including Rhinogobio cylindricus, Chanodichthys mongolicus, and Hemiculter bleekeri, etc., were dominant, which accounted for 88.76% of total number of eggs collected. 2) The scale of fish eggs each year was 83.04×10⁸ ind., 14.29×10⁸ ind., 20.43×10⁸ ind., and 22.83×10⁸ ind., respectively. 3) There were 6 main spawning grounds distributed in the upstream of Fuling sampling site in the TGR, where is an important spawning place for endemic fish species (e.g. R. cylindricus, R. ventralis, and Leptobotia elongata) in the upper reaches of the Yangtze River. 4) The daily spawning scales were mainly affected by the amounts of transparency and flow discharge during spawning, as well as flow or water level rising rate and accumulated water temperature before spawning, and the key hydrological and thermal factors that affect the natural reproduction were different among different species. This research provides data support for the implementation of fish resource protection measures, especially ecological regulation measures, in the TGR.