| Summary: | Ecosystem-based management is necessary for management of marine ecosystems because they are affected by multiple impacts, and some synergistic effects or conflicts may exist among these impacts and the possible solutions. This thesis applies three different approaches to contribute to ecosystem-based management. First, this research develops a multispecies bio-economic model that is able to consider food web interactions, different types of fisheries, and the various economic benefits provided by multiple ecosystem services. The developed model focuses on a food web consisting of migratory fish (salmon; Salmo salar), mammalian predators (grey seals; Halichoerus grypus), and schooling fish (herring; Clupea harengus) in the Baltic Sea. Additionally, the included ecosystem services include both provisioning and non-market cultural services, such as ecosystem services for fisheries, recreation and the existence of the species. By applying optimization approaches, the developed model is used to examine fisheries management. Second, structural equation modelling is applied to explore the causal relationship among climate and environmental factors, fisheries, prey availability and competitors to the salmon population. The last applied approach was ecosystem accounting, which is able to reveal the economic implications of ecosystem changes and the use of ecosystem services by different economic sectors. A framework integrating the ecosystem services and accounting system is proposed with a marine case study. Furthermore, the developed multispecies bio-economic model is applied with different valuation approaches to value the marine ecosystem for ecosystem accounting. By applying different approaches, this thesis provides insight and recommendations for ecosystem-based management from various perspectives. -
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