A cascade of dams affects fish spatial distributions and functional groups of local assemblages in a subtropical river

Spatio-temporal dynamics of fish assemblage in the Datong and Xiaotong rivers, karst tributaries in the upper Yangtze River drainage: Implications for ecological adaptation and conservation of fish in rivers

The Datong and Xiaotong rivers are karst tributaries in the upper Yangtze River drainage and represent considerable habitat diversity that contributes to high fish diversity and rich fishery resources in the two rivers. During the few decades, fish resources have abruptly declined due to overfishing, water pollution and habitat degradation. In order to further strengthen conservation and restoration of fish resources and provide scientific support for fishery management in these rivers, the temporal and spatial dynamics of fish assemblage in the Datong and Xiaotong rivers were investigated in the present study. A total of 45 species were captured at 30 sample sites during four surveys conducted from March 2016 to January 2017. Species diversity and richness both increased from upstream to downstream in the two rivers. The fish assemblages significantly differed between river reaches, while did not differ in significantly between 4 months. The spatial variations in the abundance of Rhynchocypris oxycephalus, Zacco platypus, Triplophysa bleekeri, Sinogastromyzon szechuanensis, Platysmacheilus nudiventris, Sinibrama taeniatus, Saurogobio gymnocheilus, Pseudorasbora parva, Pseudobagrus truncates and Opsariichthys bidens were considered to contribute most to the spatial pattern of fish assemblages. The lack of a temporal pattern of the fish assemblage in the rivers might be attributed to ecological habits of short-distance migration and diversified mesohabitats with riffles and pools for fish spawning, feeding or overwintering within a very short river range. Our results suggest the spatio-temporal dynamics of fish assemblages is highly adapted to the habitat characteristics in the two karst rivers. We recommend that fish conservation of these tributaries be focused on the mesohabitats, particularly the many pools and riffles.

Spatiotemporal Response of Fish Aggregations to Hydrological Changes in the Lower Pearl River, China, during the Main Spawning Season

The Pearl River is a global hotspot of fish biodiversity, yet has the most threatened endemic fish species in China. Since the establishment of the Changzhou Dam in the lower reach, changes in hydrological rhythm have negatively impacted fish downstream of the dam, but their spatiotemporal distribution in response to flood alteration has received little attention. In this study, hydroacoustic surveys were undertaken monthly in 2016 to monitor the distribution and behavior of fish. Fish densities were higher during the water discharge rising stage than during the falling stage, indicating that the fish aggregate during flooding (coefficient of variation [CV] > 100%) and depart after flooding (CV < 100%), especially aggregations of large fish. The target strength (TS) was allocated to two groups as per their frequency distributions, defined as small fish (−55 dB < TS < −40 dB) and large fish (TS > −40 dB). The sizes of both groups were significantly larger during the rising stage when compared to those during the falling stage (p < 0.01). Comparatively more fish were present with a greater average TS, and a substantially greater proportion of large fish was detected during rising stages. Hydrological variation importantly influences fish aggregations, including the numbers and sizes present, with the differences being particularly pronounced between the rising and falling stages. Combined with relevant studies, it is suggested that water releases from the Changzhou Dam should be regulated to satisfy fish spawning and migration demands during the main breeding season.