STUDY ON THE POPULATION DYNAMICS OF CARP (CYPRINUS CARPIO L.) IN THE DONG JIANG RIVER WITH REFERENCE TO THE PROBLEM OF ITS MAXIMUM SUSTAINED YIELD

Carp has been a chief commercial fish in the Dong Jiang River. Hercl, we have conducted a study on the age composition, growth, reproduction and maximum susta ined yield of this fish. Scales are used to determine the age. The relationship between the radius (R) of the scale and the length (L) of body is in linear regression. Which can be expressed as L=39.308 R—42.611. The relationship between foody length (L) and age (t) can be expressed by the equation of L1= 8511-e-0.173(t+0.0394). The weight (w)-age relationship can be described as:Wt=19171.5l—e0.173(t+0.0394)3. The first maturity of the smallest female occurs at 167 mm in length, 141.5g. in weight while male occurs at 134 mm in length, 67.3g. in weight. The individual absolute fe condity ranges from 31000 to 634803 eggs. The formula of relationship between body length (L) or body weight (W) and absolute fecundity (F) can be expressed as F=5.14*×10-2L-2.6176 and F=138.86W+17905.43 respectivaly. The total mortality of carp in Dong Jiang is calculated to be 0.52. with a. natural mortality of 0.27 and a catching mortality of 0.25. The main harvestable age at present is one year old, thus, it would be difficult to maintain the maximum sustained yield continuously. If the ma ximum harvestable age can be extended to two years of age and the harvest strength is controlled to 0.35, a 25% increment in total yield might be expected, and the original, relative abundance of the reproductive population can be maintained in a stable state.