Towards bridging biogeochemical and fish-production models

Abstract

The paper presents a theoretical approach to formulate a model which comprises the full food web. The lower part of the food web is represented by a biogeochemical model which interacts explicitly with a fish-production model. The fish-production model component builds on existing theories but was substantially reformulated in order to facilitate the model coupling. The dynamics of the fish-production model is basically driven by the predator–prey interaction. We use the example of the Baltic Sea, which has a relatively simple foodweb structure. The fish biomass is dominated by three groups, sprat, herring and cod, which represent about 80% of fish biomass in the Baltic. The zooplanktivors sprat and herring are eaten by cod. In this paper we start the construction of the model as a simple box system, which can be considered as an isolated water column of 10 × 10 km 2 times the water depth in the central Bornholm basin of the Baltic Sea. The stepwise building up of the model is illustrated by example simulations, which allow to assess the consistence of the theoretical approach and the choices of parameters. As last step we introduce a simple biogeochemical model and link it with the fish model. The resulting model system is strictly mass conserving without unspecified sources of food or so. We conduct experiments with the model system and show that it can reproduce features such as interannual variation in fish catches and trophic cascades.