珠江禁渔对广东鲂资源补充群体的影响分析

Effect of Pearl River closed fishing on Megalobrama hoffmanni recruitment stock

继我国各大水系实施禁渔期制度之后,珠江水系于2011年4月1日至6月1日实现首次禁渔。广东鲂是珠江中下游地区主要的经济鱼类之一,为分析珠江实施禁渔期制度对广东鲂资源补充群体的影响,于珠江实施禁渔制度前(2006—2010年)和禁渔制度后(2011—2012年)在珠江下游肇庆江段设立固定采样点,利用定量弶网对流经该江段的广东鲂鱼苗补充群体进行调查。结果显示,禁渔前,珠江广东鲂鱼苗集中出现在4月中下旬至10月中旬,持续时间为(189±11)d,高峰期为6—8月。禁渔期制度实施之后,全年广东鲂鱼苗出现的起始时间变化不大,但是结束时间提前,持续时间略有缩短,4—5月份广东鲂鱼苗密度明显增大。广东鲂鱼苗总量及其在鱼苗补充群体中的比例均有所提高。根据禁渔前广东鲂鱼苗发生量与径流量之间存在的回归关系:LgY=0.988Lnx-4.932(R2=0.365,P<0.01),结合禁渔后实际调查结果,对禁渔的实际作用进行了估算,2011年和2012年由于禁渔分别增加了9.43×108和651.81×108尾广东鲂鱼苗。研究表明,在径流量有保障的前提下,目前的禁渔制度可以有效增加广东鲂鱼苗补充群体资源量。

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 1 st, 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 ×10^8 ind. in 2011 and 651.81 × 10^8 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.