Marine Scotland requires a detailed understanding of fishing activity in Scottish Territorial Waters to inform marine spatial planning at both the national and regional level, and in relation to marine renewable energy development, marine nature conservation designations and fisheries mnagement. For larger fishing vessels (those over 5 m overall length) which fish mainly in offshore wters, spatially resolved information on the ctivity and the value of fishing can be derived fom Vessel Monitoring Systems (VMS) and landings data. The competition for space is, however, often greatest in inshore waters where most fishing is undertaken by small vessels which are not currently fitted with VMS. To improve knowledge of the distribution of fishing activity and the value of fisheries in inshore waters, Marine Scotland carried out a fisheries mapping study known as ScotMap. ScotMap provides spatial information on the fishing activity of Scottish registered commercial fishing vessels under 15 m in overall length.
]]>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.
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