The second half of the twentieth century has witnessed the emergence of ecological issues as among the most important problems in the global political agenda. The aim of this thesis is to demonstrate that the challenge of ecology is larger than it initially appears to be. It argues that ecological problems represent a deeper problem in the way that the relation of human being to nature is conceptualised in International Relations. The structure of the thesis works through three layers. In the first layer, chapters 1 and 2, the problems in the oceans' ecosystem are presented, with particular emphasis on ocean management system in the south Pacific Cooperation. The impact of the United Nations Convention on the Law of The Sea III (UNCLOS III) in the region and on the ecosystem is analysed with particular emphasis on the species of Tuna. In this analysis the focus is the newly formed Exclusive Economic Zones and the concept of sovereignty. The second layer, chapter 3, begins with an overview of the importance of the concept of sovereignty for the discipline of International Relations. The analysis of the deployment of the concept in UNCLOS III constitutes the middle section. The last section presents the concept of sovereignty in terms of its operational aspect. It argues that sovereign decisions always decide about an exception on life. This move opens up the philosophical constitution of the concept by pointing to the deeper relationship between human beings and nature. The third layer, chapters 4 and 5, engages with the philosophical discussion of the human subject and nature. In chapter 4, the particular anthropocentric constitution of human being through Cartesian and Kantian philosophies is critically analysed. In chapter 5, a Heideggerian formulation of human subjectivity is presented as a new ground of thinking about nature. The conclusion, then, seeks to outline more precisely the implications of the thesis' argument with respect to International Relations