Scenario - C : The cod predation model
نویسندگان
چکیده
Tittel/Title: Scenario-C: The cod predation model. Sammendrag/Abstract: The Scenario C project aims at a dynamic minimal realistic model for capelin, herring, cod, harp seals and minke whales in the Barents Sea and for herring in the Norwegian Sea. This report is an attempt to estimate a consumption function for cod from estimated monthly abundances of capelin, herring and younger cod in regions of the Barents Sea, and the observed stomach contents of cods. The data are obtained from Institute of Marine Research. A discrete choice model for the diet choice and consumption function of cod in the Barents Sea is implemented using the data of cod and three main prey species (herring, capelin, cod) from 1992-2000. It uses the notion of choice probability to describe the foraging behavior. In particular, it estimates how prey selection varies with respect to environmental changes. By using diet choice model, prey consumption can be easily computed and predicted from environmental variables. In conclusion, the empirical results are quite consistent with the hypothesis that prey selection probability is highly related to the biomass amount of the specific prey. Particularly when the biomass is at low levels, even a small increase will lead to a large probability change, with the more available biomass, the smaller the growth. At high levels, the probability is nearly linear in biomasses. As a whole, the probability change is modeled to have a logistic pattern. In addition, it shows that cod prefers capelin, rather than young cod and herring. In this paper, we try to estimate a consumption function for cod from estimated monthly biomass abundances of capelin, herring and cod in regions of the Barents Sea, and observed stomach contents of cods. Biologists and marine researchers have developed several approaches for modeling cod predation. Schweder et al (1998) present models of the logistic type for choice probabilities for minke whale and cod predations, and fit the models to data of the type we will consider. We will continue the line of research sketched by Schweder in NAMMCO (2002, page 13) by introducing alternative models for choice probabilities, and fitting these models to cod data. A discrete choice model for the diet choice and consumption function for the cod stock in the Barents Sea is implemented using the stock data of cod and three main prey species (herring, capelin, young cod) from 1992-2000. It uses the notion of choice probability to …
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