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Satellitdata för miljöövervakning och fiskeriförvaltning i Sveriges stora sjöar

Philipson, Petra; Sandström, Alfred; Asp, Anders; Axenrot, Thomas; Kinnerbäck, Anders; Ragnarsson Stabo, Henrik; Dekker, Willem


The report is a full description of the work accomplished within the SNSB user project "MERIS and hydroacoustic data for fisheries management, assessment of ecosystem status and identification of essential habitats in Sweden's large lakes". The project goal was to develop MERIS based water quality indicators for the large lakes and to employ these to predict the distribution of essential and sensitive habitats, to assess ecological status and to optimize fish monitoring. MERIS based water quality products have been developed and the possibility to use these as pressure variables in assessments of ecological quality based on metrics originating from fish monitoring has been investigated. Our results verify that predictors acquired from MERIS based water quality products can be useful for many purposes. Chlorophyll a as well as CDOM (Colored Dissolved Organic Matter), together with depth at the sampling site explained a significant part of the variation in fish assemblage composition. The major changes that normally follow eutrophication, i.e. a dominance shift to cyprinids in benthic fish communities and to young smelt in the pelagic zone, could be successfully predicted using MERIS data. Particularly CDOM and Chl a, which were highly correlated, were both strong predictors. MERIS based data layers could be a useful contribution to model the distribution of individual species and assemblages as well as the characteristics of their habitats. However, since depth in many cases is the single most important environmental factor, bathymetry maps must be markedly improved to enable modelling of the distribution of essential habitats in these systems. Another important factor that could improve the potential to model distributions would be to collect data on fish abundance and presence more evenly along the environmental gradients described by MERIS data. One example is monitoring data from hydro-acoustics that has been focused on the very largest open basins and thus do not cover the entire productivity gradient. We tested several candidate metrics to describe the influence of eutrophication on fish assemblages in large lakes using MERIS data as proxy pressure variables. In total, we were able to assess the status in thirty-one different water bodies. There were two metrics that appeared to be very promising: the density of pelagic fishes (number per hectare) and the percentage of cyprinids (when roach is excluded). We recommend that these two metrics are further explored as primary candidates for assessment of ecological status when the pressure variable is eutrophication and that the potential of a third candidate metric comprising information on age/size structure of fish communities also is investigated. To conclude, MERIS based data was a relatively powerful predictor of variation in fish monitoring data. It could be used for modelling distribution and to describe the pressure of eutrophication on water bodies in large lakes. Additionally, since the continuous maps derived from MERIS cover the majority of the lakes surface indicates that they also can be used to improve the design of field based monitoring efforts. The information can be used to ensure that the existing fish assemblages are covered and that data is representatively collected and covers the majority of the existing habitats of the monitored systems.

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Rapport från Vätternvårdsförbundet
2015, nummer: 90
Utgivare: Vänerns vattenvårdsförbund, Vätternvårdsförbundet, Mälarens vattenvårdsförbund och Hjälmarens vattenvårdsförbund.