| Based on Ecopath with Ecosim software, food web as an important cut-in point of integrated marine ecosystem research, the typical waters of the Yellow and Bohai Sea ecosystem model were constructed, including the Yellow and the Bohai Sea, the Yangtze River Estuary and adjacent waters and Laizhou Bay. The trophic interactions, energy flow, ecosystem structure and function and fishing impact on the ecosystems were analyzed, and ecological carrying capacity of stock enhancement of Chinese shrimp was discussed in Laizhou Bay. The aims of present thesis are to provide basic information for ecosystem-based fisheries management. The main results were as follows:(1) A trophic mass-balance model of the southern Yellow Sea during2000-2001was constructed, including22important functional groups and their diet composition studied. The trophic levels of fish, shrimp, crabs, and cephalopods were between2.78and4.39, and the mean trophic level of the fisheries was3.24. The trophic flows within the food web occurred primarily in the lower trophic levels. The mean trophic transfer efficiency was8.1%, of which7.1%was from primary producers and9.3%was from detritus within the ecosystem. The transfer efficiency between trophic levels Ⅱ to Ⅲ to IV to V to> V was5.0%,5.7%,18.5%, and19.7%-20.4%, respectively. Of the total flow, phytoplankton contributed61%and detritus contributed39%. Fishing was defined as a top predator within the ecosystem, and had a negative impact on most commercial species. Moreover, the ecosystem had a high gross efficiency of the fishery and a high value of primary production required to sustain the fishery. Together, the data suggest there is high fishing pressure in the southern Yellow Sea. Based on analysis of Odum’s ecological parameters, this ecosystem was at an immature stage.(2) Based on the investigations of fishery resources and environment between Autumn2000and Autumn2006, the mass-balance models of the Yangtze River Estuary and adjacent waters ecosystem were constructed during the two periods. The changes of the ecosystem structure and energy flow were compared and analyzed before and after the sluice of the Three Gorges Dam, the impact on the estuary ecosystem discussed. Since the catch of lower trophic level species increased in Autumn2006, the mean trophic level of catch declined from3.37to3.33. Relative mortalities of same diet fish groups had some changes, and fishing mortality rate was higher. The ecological efficiencies during two periods had both high values. The total biomass, system throughput, primary production and net system production of Autumn2006were higher, and the system throughput in trophic level I increased23%than that of Autumn2000. The transfer efficiency of primary producers increased, and the role of detritus in nutrient regeneration decreased. The ascendency in Autumn2006was a little higher than that in Autumn2000, and FML and FCI index was close to Autumn2000. Based on analysis of Odum’s ecological parameters, this ecosystem in Autumn2000and Autumn2006were both in developmental stage.(3) Based on the investigations of fishery resources and environment of the Bohai Sea in1982and1992, the Ecopath models of the Bohai Sea ecosystem during the two periods were constructed by the EwE modeling software. The changes of the Bohai Sea ecosystem structure and fishery resources between ten years were compared and analyzed. The models included17functional groups covering the main trophic flow of the Bohai Sea ecosystem, which were Japanese anchovy, Scaly hairfin anchovy, Japanese Spanish mackerel, other pelagic fishes, small yellow croaker, seabass, benthic fishes, other demersal fishes, zooplankton, phytoplankton, detritus, etc. The results indicated that the total biomass of1992was lower than that of1982, and small sized pelagic fishes have become the main components of the fishery resources in the Bohai Sea in1992, and the proportion was obviously higher than that in1982. The mean trophic level of catch declined in1992. The Bohai Sea ecosystem in1982and1992were both in developmental stage, and the system scale in1982was greater than that in1992. From1982to1992, the changes of the Bohai Sea ecosystem structure were mainly due to the decrease of primary production and increase of fishing pressure. Since there was high surplus production, the recovery of depleted fishery stocks and increase of fishery resources may be possible and high potential if the rational conservation measures were applied. (4) Using1982Bohai Sea model as the starting status, an Ecosim model was constructed in Bohai Sea, including the same functional groups. This model simulated the dynamic changes in different development stages of Bohai Sea ecosystem, and the fishing impact on this ecosystem, using CPUE and relative fishing effort time series to drive this model. From1982to2008, the biomass of mantis shrimp retained increasing, the biomass of main economical fishes decreased, including small yellow croaker, Japanese spanish mackerel, Japanese anchovy, seabass and scaly hairfin anchovy, and the biomass of shrimps, crabs and cephalopods relatively stabilized. The mean trophic level of catch declined obviously from1982to2008, and had notably negative correlation with the total catch. FIB index had the same change trends with the total catch, increasing after1984. Q-90diversity index was in a state of fluctuation from1982to1987, maintaining growth trend from1988tol994, followed by a rapid decline after1994, from2.5to around0.5, and ecosystem biodiversity declined. Compared start state (1982) with end state (2008) of the model, the maturity of ecosystem decreased. Overfishing resulted in the degeneration of ecosystem and the decline of the total biomass level.(5) Based on the data of surveys of fishery resources and environment from2009to2010, an Ecopath mass-balance model of the Laizhou Bay ecosystem was constructed, including26functional groups. This study analyzed the summary statistics parameters of the ecosystem, mixed trophic impacts and keystone species, and calculated the ecological carrying capacity of Chinese shrimp enhancement by Ecopath model. The ecosystem attributes statistics:the total primary production/total respiration (TPP/TR) and total primary production/total biomass (TPP/B) was1.53and24.54, respectively, together with low Finn’s cycling index (0.07), high surplus production being434.41t-km-2yr-1and low system connectance index (0.29), indicating that this ecosystem was at an early development stage according to Odum’s theory. Moreover, the analysis on the keystone species showed that Chinese shrimp was not a keystone species of this ecosystem. Current biomass of Chinese shrimp was0.1143t-km2, and Chinese shrimp has potential for continued enhancement. The biomass of Chinese shrimp could be increased25.8times without exceeding the ecological carrying capacity of2.9489t-km-2. |
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