An appraisal of factors constraining the success of fish stock enhancement programmes

Stocking and introduction of fish have been widely applied in Yunnan Province, China, for many years to mitigate for declines in natural stocks and commercial catches, and to restore or create new fisheries. The present paper assesses the results of activities concerned with stock enhancement programmes to evaluate the factors which have contributed towards the success of these projects. Factors such as natural lake conditions, stocking density, the age and size of fish stocked, and the mechanisms of stocking are discussed. Stocking density was evaluated using the equations Y _p =  B ( P / B ) U _f]/ K _f or PY_p = (P × U_f)/K_f, which were based on the ecological carrying capacity of the recipient lake and other criteria. The stocking density in most lakes in Yunnan was high, but the recapture rates and total yield did not reach the predicted levels. This may have been an effect of the size of the fingerlings released (finger-lings >10 cm have a greater chance of survival). Key management measures for stocking and the ecological impacts of overstocking grass carp, Ctenopharyngodon idella (Valenciennes), are also described.