Stocking models of Chinese mitten crab (Eriocheir japonica sinensis) in Yangtze lakes

The farming of Chinese mitten crab, a quality aquatic product in China and neighbouring Asian countries, has been developing rapidly in China since last decade. It reached a total yield of 3.4 × 105 tonnes in 2002. Due to the successive over-stocking year after year, many lakes in the mid-lower Yangtze Basin, the main farming area, are under deterioration, leading to a reduction of crab yield and quality, and, subsequently, a loss of farming profits. Aiming at a normal development of crab culture and the sustainable use of lakes, an annual investigation dealing with lake environmental factors in relation to stocked crab populations was carried out at 20 farms in 4 lakes. The results show that the submersed macrophyte biomass (BMac) is the key factor affecting annual crab yield (CY). Using the ratio of Secchi depth to mean depth (ZSD / ZM), an easily measured parameter closely correlated to BMac, as driving variable, 10 regression models of maximal crab yields were generated (r2 ranging 0.49–0.81). Based on the theory of MSY (Maximum Sustainable Yield), in combination with body-weight (BW) and recapture rate (RR) of adult crabs, a general optimal stocking model was eventually formulated. All models are simple and easy to operate. Comments on their applications and prospects are given in brief.