For monetary value, the value associated with each fishing polygon is calculated from the percentage contribution and gross vessel earnings data. Each polygon is overlaid with a grid (800 cells per ICES statistical rectangle with an average area of ca. 4.20 km2) and the polygon monetary value is divided by the number of overlapping grid cells, to equally distribute the value to all overlapping grid cells irrespective of the extent of the overlap. This process is repeated for all polygons and the values associated with each grid cell are finally summed to produce a gridded dataset.
The analysis for relative value is similar to monetary value (above) but in this case the percentage associated with each polygon, rather than the absolute monetary value, is divided equally among the overlapping grid cells, before being summed to produce a gridded data set. Treatment of the data in this way reduces the influence of larger vessels, which generally have higher gross earnings and of those vessels fishing for relatively high value species, such as lobster and scallops, often evident in the monetary value analysis. Relative value provides an alternative representation of ‘the value’ of different fishing areas. It can indicate areas important to relatively large numbers of low earning boats, and other small, often remote sea areas which are particularly important to local boats, which may be less evident in the monetary value analysis.
The number of vessels in each grid cell is the sum of the number of polygons which overlap the cell. Thus, if two fishing polygons associated with a single vessel overlap one grid cell the vessel will be counted twice in that cell and, contingent of the size of the polygon, a vessel will be counted in more than one cell. The numbers of vessels analysis provides information on the spatial extent of fishing as reported during interviews and a representation of fishing intensity i.e. where most boats fish. It is not necessarily a good indicator of fishing effort, particularly for the combined (all interview) data set, or for fisheries where activity varies seasonally. Please note all rasters shared here have been aggregated to a minimum of three vessels per cell.
For the analysis of number of crew, the average number of crew working on a vessel is attributed to each polygon for that vessel. The same value is then allocated to each overlapping grid cell and numbers summed to derive the number of crew associated with each grid cell. Please note all rasters shared here have been aggregated to a minimum of three members of crew per cell.
15 files in this archive
- National Maps/LPKs/
- National Maps/LPKs/ScotMap_Central_monetaryValue_190713_tif.lpk
- National Maps/LPKs/ScotMap_Central_numberCrew_aggr_3_230713_tif.lpk
- National Maps/LPKs/ScotMap_Central_numberVessel_aggr_3_190713_tif.lpk
- National Maps/LPKs/ScotMap_Central_relativeValue_190713_tif.lpk
- National Maps/PDFs/
- National Maps/PDFs/MonetaryValue_240713.pdf
- National Maps/PDFs/NumberCrew_240713.pdf
- National Maps/PDFs/NumberVessel_240713.pdf
- National Maps/PDFs/RelativeValue_240713.pdf
- National Maps/Rasters/
- National Maps/Rasters/ScotMap_Central_monetaryValue_190713.zip
- National Maps/Rasters/ScotMap_Central_numberCrew_aggr_3_230713.zip
- National Maps/Rasters/ScotMap_Central_numberVessel_aggr_3_190713.zip
- National Maps/Rasters/ScotMap_Central_relativeValue_190713.zip