Effect of Pearl River closed fishing on Megalobrama hoffmanni recruitment stock

After closed fishing had been implemented in the main river systems in China, it was carried out for the first time in Pearl River on April 1st, 2011.Guangdong black bream(Megalobrama hoffmanni) was one of the important economic fishes.For analyzing the effect of closed fishing on Megalobrama hoffmanni recruitment stock, the fish larvae were sampled by Jiang net at Zhaoqing section in lower reaches of Pearl River before(2006—2010) and after(2011—2012) closed fishing.The results showed that Megalobrama hoffmanni larvae usually occured from mid-April to mid-October, and duration was(189±11) days before closed fishing.And the peak density of Megalobrama hoffmanni larvae was from June to Auguest every year.After closed fishing, the starting time of Megalobrama hoffmanni larvae was without any major changes, but the end time was sooner than before closed fishing, and duration was a little shortened.The drift density of Megalobrama hoffmanni larvae increased obviously within the banned fishing periods from April to May, and the biomass and the relative abundance also rose greatly.For analyzing the effect of closed fishing on Megalobrama hoffmanni recruitment stock, the regression model was built, and the logarithmic equation was LgY=0.988Lnx-4.932(R²=0.365, P<0.01), and regression effect was significant.Based on the logarithmic equation, the fitted value of Megalobrama hoffmanni larvae was calculated, and the closed fishing effect was estimated combining actual monitored value at Zhaoqing sampling station.The increment of Megalobrama hoffmanni laevae caused by closed fishing was 9.43×10⁸ ind. in 2011 and 651.81×10⁸ ind. in 2012 respectively.The result indicates the present regime of closed fishing can effectively increase the Megalobrama hoffmanni recruitment stock based on the abundant discharge.