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A Framework for Multispecies Assessment and Management

An ICES/NCM Background Document

image of A Framework for Multispecies Assessment and Management

The report describes a framework that can be used to identify the most important trade-offs in ecosystem based fisheries management. The framework contains a description of how to identify the border between the science and policy domains, how to identify objectives and set goals for management, and how to communicate the management advice. Consultations with stakeholders showed that multi-species management advice needs to be precautionary, provide yields close to MSY, be in accordance with ecosystem constraints and be possible to communicate clearly to managers and policymakers. The use of the framework is demonstrated through examples from three different ecosystems: the Baltic Sea, the North Sea and the Barents Sea.

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Economic trade-offs

Multispecies trade-offs for management are already obvious, just taking stock sizes into account. However adding economic considerations might emphasize the need to make explicit management decisions. Here an example from a relatively simple system is given. In the Central Baltic Sea the major commercial species are cod, sprat and herring. The main interaction is the predation of cod on sprat and herring. Thus a larger cod stock might lead to smaller sprat and herring stock and vice verse. There are also some feed back interactions, which possibly strengthen the negative feedback of cod and clupeids, mainly the predation of clupeids on cod eggs. In this example the only interaction taken into account is predation of cod. The economic part in the example consists of costs of fishing and the market price of the species. Herring and sprat are schooling fish and thus the cost of fishing is relatively independent on the stock size. Cod is more dispersed and thus the cost of fishing increases when the stock decreases. The economic parameters for the model were derived from empiric al data, derived from the Annual Economic Report of the Joint Research Centre of the EU (STECF, 2011). For age-specific prices, we use the European reference prices, which are the lowest prices at which imports of cod of specific weight classes, sprat or herring into the European Union are allowed (EC 1999, 2009). The individual models were developed for Central Baltic herring, sprat and Eastern Baltic cod. They are all age-structured (8 age-classes) models to meet the standard assessment models used in ICES. The stock-recruitment function for cod and herring is a basic Ricker equation, whereas for sprat we applied a Beverton/Holt type S/R relationship. The only species interaction included at the moment is the predation of cod on herring and sprat. The equations were derived using output from the SMS model.

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