A mathematical model of predator-prey interaction between Seal, Herring and Steelhead Trout will be introduced in this article. The population of Steelhead Trout is divided into two subpopulations according to their living ecosystem, i.e in freshwater and sea ecosystem. Therefore, the model will be developed as a four-dimensional system of differential equation. The migration of Steelhead Trout is assumed to take place all over the year as a constant parameter as well as the harvesting rate in Herring and Steelhead Trout population. Mathematical analysis of the equilibrium points and local stability criteria was done. Some numerical simulation to give an interpretation about the analytical results has been conducted. The result shown that harvesting steelhead trout in fresh water has a significant impact to the ecosystem. Having the periodic harvesting strategy on the steelhead trout allows the population to recover and to ensure the sustainable harvest.