| There isa large population and relatively little arable land in China. But we have vast adjacent sea, broad continental shelf and a long coastline. The coastal sea of China is rich in biological resources. Now the coastal zoon became a major supplier of high quality protein and sea food. Further study and understand of the key process and sustainable mechanism in coastal ecosystems is necessary because it's important to the sustained exploiture of sea biological resources, and thus to the country's food safety.Anchovy is a kind of small pelagic fish live in temperate sea, widely distributed in the Bohai Sea, Yellow Sea and East China Sea. It's the food for many commercial fishes. In China, since the mid-1980s, as resources of major commercial fishes declined, anchovy is no longer a subordination object of fishery but become a main object. The output increased obviously. However, due to overfishing, anchovy resources have declined. Recent years, anchovy have almost disappeared in adjacent sea. This shows it is extremely necessary to strengthen fisheries management. Fish resources should be fully utilized while its ecological balance should be maintained. The main purpose of this study is to establish an ecological model of anchovy, study the mechanism of changes in anchovy population, provide the scientific basis for the sustainable development of China's coastal ecosystems and a responsible fisheries and fishing management system.In recent years, individual based model (IBM) has been widely studied and used. A large number of individual objects are simulated in IBM while the differences between individuals and the influence of spatio-temporal changes of environment are considered. Based on the statistics, the population level attributes are got. Previous studies show that it is of great significance to consider individual differences and environmental heterogeneity in a population dynamics model. Therefore, IBM is used in this study. 2D unstructured triangular grids are used in this model. Environment factors for anchovy are calculated in triangular cells. Environment includes physical factors and low trophic level organisms. In this model, water temperature is the only physical factors which directly affect anchovy's behavier. Anchovy prey on zooplankton. The biomass of zooplankton is supplied by NPZ model. NPZ model takes the nutrients, phytoplankton and zooplankton as the variables and considers the influence of solar radiation and water temperature.In this IBM model we established, length, weight of individual anchovy and abundance are the variables. The ingestion, metabolism, swimming, spawning, death of anchovy and hatching of eggs are considered. The simulation starts when an anchovy is older than 45 days. The swimming of anchovy depends on their individual behavier and environmental conditions. Each anchovy individual integrates environmental temperature and the density of food (zooplankton), and in light of its own characteristics, the fitness of the environment where it lives and that of the surrounding environment are calculated. Fitness gradient, swimming ability (related to body length) and two random numbers decide the direction and speed of anchovy swimming.For anchovy, the individual difference not only include phenotype differences, such as difference in body length, body weight, swimming ability and spawning ability, but also include the intrinsic differences(genetic difference), which is even more important. From the biological perspective, the individual genes and the environment decide the individual phenotypes together. Previous studies have accumulated large amounts of data and empirical formulas, these formulas describe the individual's physical condition and the rule of growth. There are many parameters in these formulas. In the model, parameters which are constant during the life are defined as gene. Parameters which varies with individual age, state or season is defined as semi-gene. It is assumed that semi-genes are continuous piecewise liner functions of age, season and body length. The value of the semi-gene on the section nodes is defined as geneand the value of the semi-gene can be calculated real-time. Genes are inherited from parents, while some variation takes place. In the model parameters which are same between individuals are defined as population parameter.With the passage of time, individual phenotypes renew. Some individual starved to death as a result of competition, some frozen to death as a result of low environment temperature, some others are forced to death because of abnormal phenotype. In spawning season, anchovies with certain age, length and fullness and in spawning grounds lay eggs.Through survival choice, reproductive choice and genetic variation and heredity, evolution of anchovy is simulated in this model. Appropriate use of the model can optimization many parameters which are difficult to identifyIn this model, temperature field and food density field are used to driven anchovy swimming, reproduced the migration of anchovy. Experiments were made by changing environment temperature and fishing effort. The population distribution, biomass, age structure and body length of anchovy under these conditions are studied. The results are close to or in qualitative agreement with the observed values.The study shows that when the temperature rises, the spawning migration will be advanced, while the wintering migration will be delayed, the distribution will be changed in the same time. As long as the change of temperature is not too much, its impact on biomass will be little. But when it changes too much, the stock of anchovy will decrease.Simulation results show that when fishing effort is small, sustainable catch will increase with fishing effort, when sustainable catch reaches its maximum, when fishing effort increases, catch will first slowly decreases ,then reduces sharply, even results in the extinction of species. This told us when catch don't increase with fishing effort, fishing effort should be reduced properly.
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