This paper presents a method to evaluate the effects of different fisheries development intensities on aquatic vegetation by using a geographic information system (GIS) in Honghu Lake, one of the largest shallow lakes in the middle to lower reaches of the Yangtze River. Data for aquatic plants surveyed at 34 sampling stations in July 1992 were employed for this application. The aquatic plants were divided into two categories: aquatic plants favoured (APF) or not favoured (APNF) by fish, respectively. The aquatic plant utilization, which represents different fisheries development intensity, in a sampling stand was defined according to its biomass and species composition (APF or APNF dominated). Four different utilization levels were distinguished: low, high, long-time restoration after over-utilization and short-time restoration after over-utilization. For each utilization level, four sample stands were chosen to obtain the biomass-water depth relation, which was then applied to obtain the distribution of biomass over the entire lake. Under low and high utilization levels, the simulated average biomass was 7420 and 5260 g m-2 respectively, with APF contributing most to the standing crop. The restored biomass after over-utilization depends on restoration time. The simulated average biomass of short-time restoration was 5530 g m-2 with APF 500 g m-2. The calculated average biomass of long-time restoration would reach 12360 g m-2 with APF 720 g m-2. Limiting the scale of fish-pen-culture and improving the way of utilizing aquatic plants favourable to herbivorous fish is vital for sustainable development of the lake. |
