Chen L

A comparison between benthic gillnet and bottom trawl for assessing fish assemblages in a shallow eutrophic lake near the Changjiang River estuary

Two fishing methods including gillnetting and trawling to estimate attributes of fish assemblage were compared in Dianshan Lake from August 2009 to July 2010. Species composition differed significantly between the gears, with four significant contributors in gillnet catches and one in trawl catches. Trawling collected more proportions of benthic species by number and biomass than gillnetting. Size distribution was significantly influenced by fishing technique; gillnetting captured relatively less small-sized fishes and trawling captured less large-sized individuals. Trawling produced species richness closer to the one expected than gillnetting. On the whole, trawl catch was a quadratic polynomial function of gillnet catch and a significantly negative correlation was found between them, both of which varied as different polynomial functions of temperature. However, trawl and gillnet catches were significantly correlated only in one of five month groups. It is concluded that single-gear-based surveys can be misleading in assessments of attributes of fish assemblages, bottom trawling is a more effective gear for assessing fish diversity than benthic gillnetting, and using gillnet catches as an indicator of fish density depends on fishing season in the lake.

Spatial variations of macrozoobenthos and sediment nutrients in Lake Yangcheng: Emphasis on effect of pen culture of Chinese mitten crab

We determined the effect of Chinese mitten crab (CMC) pen culture on the quantified spatial distribution of the macrozoobenthic community and sediment nutrients in Lake Yangcheng. Redundancy analysis indicated that water temperature, macrophyte occurrence, sediment type, and crab culture were the main environmental factors that influence the spatiotemporal macrozoobenthic distribution. Macrozoobenthic assemblages in the lake were characterized by eutrophic indicator species. In the most polluted estuaries, the abundance and diversity indices of the whole community and abundance of chironomids and oligochaetes were significantly depressed, and sediment carbon (C) and phosphorus (P) were significantly enhanced compared with those in the western, middle (MB), and eastern basin (EB). Crab culture in this lake had significant effects on the species composition of the macrozoobenthic community in one of three CMC culture pens (CP), and generally depressed the abundance of most chironomid and oligochaete species. Significantly increased diversity, evenness, sediment carbon and nitrogen content, and sediment C:P ratio in the CP were found compared with those in the three basins. However, no conspicuous difference in sediment P content between the CP and the two basins of MB and EB was detected. Our results showed that the enhanced diversity and evenness of macrozoobenthos might be associated with the joint effect of macrophyte planting and crab predation, and macrophyte planting may modify the effects of CMC culture by leading to disproportional accumulation of C and N in the sediment relative to P in the CP of the lake.