Spatial distribution and abundance of small fishes in Xiaosihai Lake,a shallow lake along the Changjiang (Yangtze) River, China

Spatial distribution and abundance of small fishes were studied in autumn 2007 in the Xiaosihai Lake, a shallow lake along the middle reach of the Changjiang （Yangtze） River. Based on the plant cover, the lake was divided into three major habitats： Myriophyllum spicaturn habitat （MS habitat）, Trapa bispinosa habitat （TB habitat）, and non-vegetation habitat （NV habitat）. A modified pop-net was used for quantitative sampling of small fishes in the three habitats, and the Zippin＇s removal method was used for estimating densities of the small fishes. A total of 13 species belonging to 5 families were collected, with 11 species in MS habitat, 7 species in TB habitat, and 5 species in NV habitat. Habitat type had significant effect on the spatial distribution of small fishes. The Shannon-Wiener diversity index in the MS, TB and NV habitats were 1.28, 0.56 and 0.54, respectively. The total density and biomass of small fishes were significantly higher in the MS habitat （13.68 ind/m^2 and 4.44 g/m^2） than in the TB habitat （1.41 ind/m^2 and 0.54 g/m^2） and the NV habitat （1.08 ind/m^2 and 0.40 g/m^2）, and were not significantly different between the TB habitat and the NV habitat. Water depth had no significant effect on spatial distribution of the small fishes. It was suggested that vegetation type played an important role in habitat selectivity of small fishes, and the presence of submersed vegetation should be of significance in the conservation of small fish diversity.

肖四海湖五种渔具的鳜渔获结构特征及其对鳜资源的影响

为评估不同渔具对鳜资源的影响,于2007年5月和12月对长江中游浅水湖泊肖四海湖刺网、延绳钓、网簖、电拖网和电捕仪5种渔具捕获的鳜渔获物结构特征进行了调查分析。结果发现,共采集鳜样本359尾,全长分布范围为92-600 mm,优势全长集中于251-350 mm;体质量分布范围为10-3 380 g,优势体质量集中于300-500 g。种群由5个年龄组构成,2-3龄为优势龄组,占总数的74.6%。刺网、延绳钓和网簖对鳜有较强的捕捞选择性,网目大小为80 mm和100 mm刺网的鳜渔获物中2龄及以上成熟个体占总数的93.3%,个体平均体质量466 g,＂标鳜＂（0.4-0.75 kg）个体占总数量的57.0%;延绳钓捕获的鳜渔获物中2龄及以上成熟个体占总数的86.9%,＂标鳜＂个体占总数量的43.5%;网簖捕获的鳜渔获物中90%以上为1龄的未成熟个体。电拖网和电捕仪捕获的鳜全长范围明显较大,其渔获物以1龄和2龄个体为主。综合分析表明,刺网适于作为鳜捕捞的主要渔具,延绳钓可以作为一种鳜捕捞的辅助渔具。网簖对鳜补充群体有较大危害,不适于作为鳜的捕捞网具。电拖网和电捕仪均属于违法渔具,对鳜资源危害巨大,应该加大监管力度,严禁使用。

肖四海不同渔业发展阶段的水环境特征分析

2006-2008年,对长江中游的一个浅水湖泊——肖四海进行了水质和水生植被研究,并结合历史资料分析了肖四海1987-2008年不同渔业发展阶段的水环境特征。研究结果表明：1987-2008年期间,该湖营养状况经历了中营养→富营养→中营养→富营养→中营养的变化过程,沉水植被经历了消亡→恢复→旺盛→衰退的演替过程,这种变化主要受不同阶段的渔业方式的影响。草食性鱼类和河蟹的过量放养、化肥的大量使用以及饵料的大量投放等不合理的渔业方式导致了水生植被的消亡和水体的富营养化,而合理的渔业方式不会对水体环境产生消极影响,并据此提出了长江中下游湖泊渔业可持续发展的建议。