Maintenance of yield maximization and species conservation perspective in a three species food chainmodel

摘要

In this paper we develop an outline of possible impacts of applying Maximum sustainable yield (MSY) and Maximum sustainable total yield (MSTY) policy in a ecosystem consisting of prey, first predator and second predator and investigate on different coexistence and extinction scenarios under certain ecological conditions. Generally we have found that application of MSY in single species system or MSTY in multi species system may cause the extinction of several species. In traditional prey predator system fishing under combine harvesting effort may not be a sustainable policy due to the extinction of predator species. But in case of a generalists prey predator system fishing of any one species at MSY level is always a sustainable policy. But in our considered food chain system we have found that when there are more than two trophic level harvesting of the highest trophic level may or may not be a sustainable policy. We have studied throughly the impacts of applying MSY and MSTY policy in different trophic level or combination of trophic level in three species food chain system where predators are generalists in nature. In addition, we have also investigated the role of catchability coefficient of different trophic level on the existence of MSTY andon the quantity of yield as well as on the equilibrium stock density. Our study reveals a trade off between a prey-oriented effort with higher amount of yield and also risky from conservation view point and a top predator oriented harvest with lower yield but sustainable in terms of conservation in a three species food chain system with generalist predators.