Cel The aim of the research is the continuation of the development of the multispecies virtual population analysis (MSVPA) by: extending it into an area based model in which the spatial overlap between fish predators and prey is accounted for; including a dynamic description of the size at age of prey as a function of predation mortality; incorporating a description of the predation by other predators (seals, birds, rays, etc); exploring alternative models of food selection; and studying the sensitivity of the model to changes in the level of recruitment. The project continues the development of the Multispecies Virtual Population Analysis (VPA). As part of the computer package 4M the area based multispecies VPA has been implemented and tested. The package constitutes an integrated package including historic analyses, predictions based on these and database facilities. The package contains 2 different types of approaches for conducting area based analyses. One approach assumes that full information (catch and stomach content data and migration) is available for a historic period. In this case a multispecies VPA can be carried out for each of selected subdivisions separately. However, using the standard multispecies VPA estimation method estimation problems are encountered with respect to stock size and fishing mortality. The second approach offers the possibility of estimation of area based parameters based on one year's intensive collection of data. Both approaches makes it possible to perform area based predictions. The basis for a length based VPA method including a tuning module has been formulated. The method is formulated as a forward minimalization algorithm based on the usual catch equation, a growth equation and a model for linking the tuning data with the stock parameters (eg stock abundance or fishing mortality). The approach presented is in close accordance with the ideas behind the much used methods for age based VPA and Extended Survivors Analysis (XSA). The multispecies VPA (MSVPA) was modified to allow inclusion of other predators, for which data on biomass, food intake and food composition are available. The inclusion of starry ray and western mackerel as other predators increased predation mortality and recruitment estimates significantly for herring, sprat, Norway pout and sandeel. The effect of including prey and predator switching in the MSVPA for the North Sea was examined. Switching was modelled by making suitability a function of prey abundance. The results were evaluated by comparing observed and estimated stomach contents. It is concluded that additional stomach content data are needed to evaluate the significance of switching in the North Sea. The multispecies prediction program (MSFOR) was modified in order to allow the relative changes in yield and biomasses resulting from a change in fishing mortality to be evaluated at various recruitment levels. The model was used to predict the consequences of an increase in mesh size to 110 mm in the roundfish fleet. Although multispecies predictions are highly sensitive to recruitment the results show that conclusions that are independent of recruitment changes can be drawn in some cases.The development of the MSVPA will consist of elaborating the current FORTRAN program and of parameter estimation based on existing data from surveys and from the commercial fishery. The work will be divided into 5 subprojects which are undertaken in a total of 6 phases as follows. The model will be extended to include a description of the predation mortality generated by other fish predators such as seals, birds, rays, etc for which no catch at age data is available. The data on stock size, food composition and rate of food intake for the most important species will be summarised and used as input to the model. Available information on the migration patterns will be summarised and a first outline of an area based model will be made. The effect of making suitability a function of prey availability will be studied. Comparisons between observed and estimated stomach content and between MSVPA estimates of year class strength and survey indices will be used to evaluate whether switching is likely to be of importance in the North Sea. The model will be extended to allow 2 or more fishing strategies to be compared directly in terms of percentage changes in yield from a baseline run. The sensitivity of the conclusions to variations in recruitment will be evaluated using an experimental design approach. A simple continuous model of the growth of individual cohorts will be developed with the aim of explaining how the average size of the individuals depend on total mortality. The model will be incorporated in the MSVPA and tested by comparing the results with length distributions obtained during surveys. Based on the information collected under the second phase, a migration model will be constructed. This model will be used to extend the MSVPA to an area based model. Dziedzina nauki agricultural sciencesagriculture, forestry, and fisheriesfisheriessocial sciencessociologydemographymortalitynatural sciencescomputer and information sciencesdatabasesnatural sciencesbiological sciencesbiological behavioural sciencesethologybiological interactionsagricultural sciencesagricultural biotechnologybiomass Program(-y) FP2-FAR - Community research and coordination programmes (EEC) in the fisheries sector, 1988-1992 Temat(-y) Data not available Zaproszenie do składania wniosków Data not available System finansowania Data not available Koordynator Danmarks Fiskeri og Havundersoegelser Wkład UE Brak danych Adres Charlottenlund Castle 2920 Charlottenlund Dania Zobacz na mapie Koszt całkowity Brak danych
