| Summary: | 碩士 === 南華大學 === 環境管理研究所 === 92 === The over-harvesting of fishery resources has leaded to exhaustion of fishery stock around the island. Moreover, the environmental pollution along the coastal line also aggravated the environmental deterioration and consequent resource depletion. Past empirical studies by experimental researches and practical programs find that the artificial reefs (ARs) as a fishery habitat that can change the water flow to improve the environment for fishery. In this case, the construction of ARs in the sea is an effective way to restore the fishery stocks and improve fishermen’s income. As most constructed ARs in Taiwan were not taken care duly, the service life was much shorter then that in developed countries.
In this paper, if fishery resources are seen as a private ownership, we attempt to analyze the cost benefit of an ARs construction through the proposed artificial reefs harvesting model to accomplish the optimal harvesting strategies. Since an ARs ecosystem has its characteristic existence, it will be buried and scoured later due to its finite service life; and when the ARs is deemed to the private goods, it would be a non-closed ecosystem because of its permeable boundary. For this reason, this study incorporates with the population dispersal dynamics (Buechner, 1987; Stamps et al., 1987) into the conventional open access fishery management model to conform to the characteristic of practical application in ARs. An optimal number of fishing boats and the timing to dispatch the boats (i.e., control variables U and τ) at steady state are obtained by using optimal control theory with the Most Rapid Approach Paths (MRAP). Then we transform the optimal control problem into static optimization problem. Sensitivity analyses on the effects of environmental parameters on optimal harvesting strategies are analyzed.
The results reveal that the fishery firm will dispatch more fishing boats as early as possible to achieve the maximization of profit in case of the following situations: discount rate is increased, area of ARs is expanded, target species move less mobile, the price per unit catch increases, and operation cost is decreased. This harvesting strategy is also constrained by the rule that the profit rate (i.e.,1-b ) must be greater than the ratio of population loss rate to intrinsic growth rate (i.e., λ/r0 ). In brief, the effect of permeable boundary in ARs ecosystem has been considered and incorporated in our model presented in this paper. The major contribution of this paper is our focus on open populations of mobile, long-lived species, boundary type and geometrical configuration of an ARs ecosystem that plays an increasingly crucial role in determining the potential equilibrium population size.
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