GIS-aided spatial analysis of fish abundance and biomass in the Bulgarian Black Sea

Geographical information systems (GIS) are commonly used as a supplementary tool in fisheries analysis. We used tabular data containing calculated indices of catch per unit area (CPUA) and biomass regarding 5 target species. These post-expedition data were integrated into GIS by using the trawling locations coordinate records. The latter were subsequently exported as georeferenced points containing CPUA and biomass values in the shapefile attribute tables. These values were interpolated into grids using inverse distance weighting (IDW), with the interpolation procedures applied for each of the 5 species and each expedition separately. The resulting raster files were reclassified converting the quantitative data from stretched values into interval breaks. The interpolation results were illustrated as digital maps. The study proves that GIS represents an effective tool in fisheries assessments, especially when using IDW. However, the credibility of this approach is highly dependent on the input data and the point densities, therefore GIS cannot replace entirely the analysis/assessment expertise by experienced ichthyologists. Nevertheless, GIS and georeferenced data remain of crucial importance.