Conservation Biology Of Rare And Endemic Fishes Of The Yangtze River

There are about 300 fish species in the Yangtze River, out of which 267 species, including 117 endemic species, distributes in the upper reaches. However, the construction of the hydroelectric projects, such as the Gezhouba Dam, the Three-Gorges Dam, and hydropower cascade exploitation in the Jinsha River, drastically modifies physical environment and regulates flow in the Yangtze course. This causes habitats fragmentation, blocks migration routes, and destroys spawning grounds, leading to the severe negative impacts on the rare and endemic fishes of the Yangtze River. Additionally, due to lack of strict and scientific management, the resources of the fishes in the Yangtze River are overexploited severely. In particular, the decline of the endemic fish resources has occured and the stocks of many species have been at the depleting stage. Therefore, it is eagerly needed to pay more attentions to preserve the rare and endemic fish resources of the Yangze River. In this case, based on the long-term data of our lab, conservation biology of the rare and endemic fishes, such as Chinese sturgeon (Acipenser sinensis), Ancherythroculter nigrocauda and Megalobrama pellegrini, was studied by using modelling techniques, such as population viability analysis and per recruit models, with the purpose to provide information for instituting and implementing the conservation measures.This study is composed of three sections. The main results are as following:In the first section, a population viability analysis using VORTEX model was conducted to evaluate the effects of Gezhouba Dam to Chinese sturgeon (Acipenser sinensis) in the Yangtze River and conservation measures. The results indicated that (1) population size might decline drastically further and comprise only 16.8% (0.3%-90.4%) of its original population size after the fish has propagated density-dependently for 100 years, but the density-independent population almost sustains stable (101.4%). This means that the Gezhouba Dam is mainly the reason responsible for the decline of Chinese sturgeon population. (2) The actual restocking strategy, which constitutes the main conservation measure, could probably be insufficient to improve population sustainability. It was needed to increase the efforts on restocking more number of artificially produced fingerlings. Therefore, the artificial propagation and rearing fingerlings technique should be improved urgently, especially the complete artificial propagation and releasing. Morover, the restocking program should imperatively be guided by genetic study. (3) The increase of carrying capacity of spawning ground and early survival rate was helpful to improve population status. The alternative conservation measures should be carried out as soon as possible, such as creating new spawning ground artificially, decreasing loss of eggs consumed by predators and juvenile catches in the estuary.The second section was to assess the status of the stocks of Ancherythroculter nigrocauda and Megalobrama pellegrini in the Longxi River and discuss the management strategy. The results indicated that (1) at present both these two stocks had been overexploited far beyond the ideal target (F40% and F0.1) and threshold (F25%) of fishing levels. The percentage of the spawning stock biomass of the current fishing level to that of the pristine level was estimated to be merely 6.96% for A. nigrocauda and 8.72% for M. pellegrini. This may possibly lead to high risk of the recruitment failure in the future. (2) Management strategies were discussed in order to maintain the stocks based on the curves of yield per recruit and spawning potential ratio. The results suggested that the approach for determining catch limit and minimum size limit could be effective to preserve the resource of these two endemic fishes. Particularly, based on natural mortality rates, the catch limit and minimum size limit could rationally be combined to obtain high yield at minimum risk. The third section was to assess the impact of the filling of the Three-Gorges Reservoir on the fish resources by researching the catches. (1) According to the research of the catches in Yibin, Hejiang, Mudong, and Yichang reaches of the upper Yangtze River conducted from 1997 to 2006, it was indicated that although the filling of the Three-Gorges Reservior could not result in the evident change of CPUE of each reach, the resources of the endemic fish of the upper Yangtze River trended to be depleting. Moreover, after the filling, dominant degree and proportion of those lentic species which distributed widely, such as Silurus meridionalis Chen, Cyprinus (Cyprinus) carpio Linnaeus, and Leiocassis longirostris Günther, increased evidently. Particularly, in Yichang reach the dominant species had a evident change after the filling. Five species,such as Hypophthalmichthys molitrix (Cuvier et Valenciennes), Ctenopharyngodon idellus (Cuvier et Valenciennes), Leiocassis longirostris Günther, Rhinogobio ventralis (Sauvage et Dabry), and Silurus meridionalis Chen, lost the dominant status. Dominant degree of two endemic species, Coreius guichenoti (Sauvage et Dabry) and Rhinogobio ventralis (Sauvage et Dabry), drastically decreased due to the embarrassment which juveniles and eggs difficultly passed through the Three-Groges Dam. Ctenopharyngodon idellus (Cuvier et Valenciennes) and Hypophthalmichthys molitrix (Cuvier et Valenciennes) disappeared in the catches because the resources were severely destroyed. (2) The investigations of the catches were conducted in the Wanzhou and Fuling reaches of the Three-Gorges Reservior in 2005 and 2006, respectively. The results indicated that the lotic water became the lentic water in the reach of the reservior after the filling. Although CPUE of the reaches in the reservior did not had a evident change after the filling, the composition of the catches was influenced significantly. The lotic fishes, such as Ctenopharyngodon idellus (Cuvier et Valenciennes), Coreius heterodon (Bleeker), and Hypophthalmichthys molitrix (Cuvier et Valenciennes) were enforced to move upstream to the lotic water, leading to their proportion decreaseing and dominant status replaced by the lentic fishes. The Three Gorges Dam and the hydropower cascade exploitation destroyed spawning habitats of the fishes of the upper Yangtze and modified the composition of the fish community, which severely threatened the fish rescources of the upper Yangtze. Therefore, the conservation strategies should be carried out as soon as possible, such as the artificial propagation and releasing, catch limit, and the construction of the fishes reserve.