Modelling production and biomasses of prey and predatory fish in lakes

  • Håkanson L
  • Boulion V
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Abstract

This work presents a new dynamic model to predict two fundamental functional categories of fish in lakes, prey and predatory fish. The model has been developed within the framework of a more comprehensive lake ecosystem model, LakeWeb, which also accounts for phytoplankton, bacterioplankton, two types of zooplankton (herbivorous and predatory), zoobenthos, macrophytes and benthic algae. The new fish model gives seasonal variations (the calculation time is 1 week). It is meant to account for all factors regulating the production of fish for lakes in general. The model has not been calibrated and tested in the traditional way using data from a few well investigated lakes. Instead, it has been tested using empirical data and regressions based on data from many lakes. The basic aim of the model is that it should capture typical functional and structural patterns in many lakes. It accounts in a relatively simple manner for many complicated processes, like fishing (by birds, animals and man), fish migration to and from lakes and how macrophyte cover gives shelter to small fish and reduces predation pressure. Food choices are handled by distribution coefficients regulating how much of the different available food sources a given organism would consume. Beside these distribution coefficients, and the way the food choices are structured (the food choice panel), fundamental concepts in the fish model are: (1) metabolic efficiency ratios, which express how much of the food consumed by the predator that will increase the biomass of the predator and how much that will be lost by respiration and faeces, (2) actual consumption rates, which are defined from the ratio between the actual biomass of the predator and the normal biomass of the predator, and the normal consumption rates, which are related to the turnover time of the predator. We have demonstrated that the new model gives predictions which agree well with the values given by the empirical regressions, and also expected and requested divergences from these regression lines when they do not provide sufficient resolution

Author-supplied keywords

  • Biomass
  • Environmental factors
  • Lakes
  • Macrophyes
  • Models
  • Predation
  • Predatory fish
  • Prey fish
  • Production

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Authors

  • Lars Håkanson

  • Viktor V. Boulion

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