Population Ecology Of Rhinogobio Ventralis In The Upper Reaches Of The Yangtze River

Rhinogobio ventralis (Sauvage et Dabry), an endemic and commercially important fish; widely distributed in the lotic habitat upper reaches and stream of the Yangtze River. However, the construction of hydroelectric projects and ruins its habitat, drastically modifies physical environment in the Yangtze River. Therefore, it is eagerly needed to pay more attention to protect the R. ventralis resources in the Yangtze River. Based on the investigation data of fishery resources in Panzhihua, Yibin, Hejiang, Mudong and Wanzhou of the upper reaches of the Yangtze River during the years from 1997 to 2007, the present study indented to investigate the age and growth, population structure, population mortality and recruitment pattern of the R. ventralis, and carry forward its conservation approaches. The main results are as following:1. The results revealed that the clear scales are reliable for determining the ages of the R. ventralis. The agreement of two times examined on scale is 89.6%.2. The relationships between total weight (W) and standard length (L) were described as: W=7 x 10-6L3.1411. The growth of R. ventralis belongs to allometric speed type, which can be described by Von. Bertalanffy equation. The growth equations of standard length and total weight are as following: L=554.5(1-e-0.23((?)+0.6)) W=2910.5(1-e-0.23((?)+0.6))3.1411The maximum standard length (554.5 mm), maximum total weight (2910.5 g), growth parameter (0.23) and theoretical standard length zero-point (-0.6 a) were observed. The growth performance indices (4.85), total weight growth inflexion point (4.3 a) with corresponding standard length (374.8 mm) and the body weight (850.8 g) at the maximum age of 12.44 a.3. The R. ventralis population was a relatively complex in age structure which has 6 different age groups from 1 to 6. The majority is from 1 to 3, and occupies 89.13%. The number of individuals was declined sharply after 4 age. The standard length of the population ranged from 24 to 307 mm, mostly occupied in 80-200 mm size groups, which accounted 94.84% of the total population. The body weight varied from 0.1 to 484.0 g, mainly in 0.1-150.0 g, which accounted 95.79% of the total. The variation of the mean standard length and body weight of the R. ventralis was in an increasing trend the sampling sites. The overall sex-ratio of the population is♀:♂= 1.2:1.4. The total mortality coefficient (Z) estimated by using the length-converted catch curve which is 2.22, total mortality rate (A) is 88.45%, and it is in a increasing trend about the total mortality coefficient (Z) during 1997 to 2007; the natural mortality coefficient (M) calculated with Pauly's empirical equation is 0.43, natural mortality rate (V) is 17.13%; the fishing mortality coefficient (F) is 1.79, fishing mortality rate (U) is 71.32%.5. The main tpyes of fishing gears for catching the R. ventralis are trammel-net, set gill net. However, the capture efficiency of the trammel-net for the R. ventralis is far height than other fishing gears.6. Recruitment pattern of R. ventralis analysis indicated that the continuous recruitment period is from May to August, which account of 76.94 of the total. The rate of exploitation (E) in recent years was 80.63%, and the resource of R. ventralis was on the state of overexploitation.7. The most threatens of the R. ventralis are the construction of hydro-projects and overexploitation. To conserve the resources of the R. ventralis, strategies include erecting the fishes reserve, prohibiting fishing of juveniles less than 160 mm and extends fishing ban period.