Impacts of fishery on marine ecosystem.Fishery is one of the mostin fluential human activities
on aquatic ecological systems. Due to continuous and selective removal of the top predator during
fishery processes, the predation pressure is reduced and the top-down effect is dramatic on the
structure of ecosystem. The Ecosim module can dynamically simulate the influence of fishery policy
and environmental disturbance on the production and the amount of the resource in a certain period of
time. Pauly et al summarized the results from over 60 studies based on the Ecopath model, and
showed that the global mean trophic level of the fisheries landings decreased from slightly more than
3.3 in the early 1950s to less than 3.1 in 1994 (Fig. 1). The reason is that with increase of fishing
pressure, the catches gradually change from carnivorous, demersal fish of long-life time to pelagic
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fish of plankton feeding and short-life time. Correspondingly, the fishing yield was first increased
and then reduced, suggesting that the global fishery resources have been over-exploited and the
development is not sustainable [6].