Growth And Population Characteristics Of Coreius Guichenoti (Sauvage Et Dabry) In The Upper Reaches Of Yangtze River

Largemouth bronze gudgeon (Coreius guichenoti Sauvage et Dabry), which is endemic to the upper reaches of Yangtze River, is an important commercial fish. However, at present this valuable species is seriously threatened by the environmental pollution, over fishing and the detrimental effects of the hydropower projects prevailing in the middle and lower reaches of Jinsha River and Yalong River. Starting from the growth model analysis of individuals, this thesis explored the demography characteristics of the population and finally analyzed the status of this population based on the parameters derived from the first two steps.First of all, the growth function of the largemouth bronze gudgeon was analyzed in chapter 2 based on the data from surveys conducted in the upper reaches of Yangtze River from 2005 to 2007. Results showed that the relationship between scale radius and body length corresponded to the equation L= 85.429S0.8125(R2=0.9635, no significant difference between males and females at 0.01 level). The body length from back-calculation showed apparent Lee's phenomenon. Non-linear mixed model method together with AIC was used to provide the best estimate of growth parameters. Back-calculation data was fitted to 36 models based on a group of 4 candidate growth equations, which were von Bertalanffy (VBG), Richards, Gompertz and Robertson growth equations. According to AIC in the sequence of goodness of describing the growth of the largemouth bronze gudgeon, these growth equations were VBG, Richards, Gompertz and Robertson growth equation. The best model was VBG Model 6:Lt=602.9[1-e-0.1693(t+24)] (no significant difference between males and females at 0.01 level) with growth performance indexφ=4.7891±0.01612. Through the analysis, I found that it was better to use back-calculation data and non-linear mixed model combined to describe the growth pattern of fish showing apparent Lee's phenomenon than the least square method.Secondly, with the aim of providing data to population viability analysis, the population characteristics were studied in chapter 3 through the analysis of the catch survey data in the upper reaches of Yangtze River from 1998 to 2007. Results indicated that many kinds of fishing gears enmeshed the largemouth bronze gudgeon, and of those the trammel net, crochet, chuan zeng net and set gill net were the frequently used ones. Different primary fishing gears were used in different reaches of the river. By the analysis of the relative biomass index in different reaches from a series of years, it was clear that the population density center moved upstream after the water storage of the Three Gorges Dam. Lower age classes dominated in the growing type age structure. In the reproductive age category, the maturity ratio rises from age 4 to age 6 and individuals older than age 6 have a ratio of 1. Considering the demographic characteristics and habitat change imposed by the construction of hydropower projects, I suggest more cautiousness about the exploitation of the natural resources of this species and more research on the population viability models in the future so as to confer conservation strategies for this population.Thirdly, the population growth rate, reproductive contribution at different age groups, stable population age structure and vital rates elasticity to the population growth rate by using the Leslie matrix model were studied in chapter 4 based on the demographic parameters and life history vital rates. Results showed that 1-year-olds mortality rate was 0.2024%, and the average absolute fecundity of 4 to 7 year-olds were 249.2,1 247,24 230 and 32 660 eggs, respectively. And the life table of this species was also presented. Leslie matrix analysis demonstrated that the population was declining with a finite rate of increase of 0.8589. The elasticity analysis showed that reproductive parameters had a major elasticity percentage of over 99%, while survival rates had a minor elasticity percentage of merely 0.0024%; and the survival rate of 2-year-olds had a larger elasticity than any other age class.Finally, this thesis discussed several potential threats facing this species and urgent measures to be taken for the conservation of this population.