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Global Fisheries Data

by Matthew Perry — last modified 16-06-2006 16:11

Global fish catch data is first classified into fishing methods, associated with point locations, converted to a raster grid, then adjusted by primary productivity of the surrounding are. This technique gives us a ratio of fish catch to productivity - a useful measure of fishing pressure for each method.

Overview

The fish catch data was aggregated by 5 different fishing methods:

  1. Palagic, high bycatch
  2. Palagic, low bycatch
  3. Demersal, destructive
  4. Demersal, non-destructive, high bycatch
  5. Demersal, non-destructive, low bycatch


Each catch rate is associated with a particular point location. It is then rasterized and normalized by primary productivity to give an indicator of global fishing pressure.


Methods

  • Export the the point locations table to dbf files
  • Add XY data in ArcMap to convert the location table into a point dataset. Save as shapefile.
  • select for each catch type and export a seperate dbf
  • join each dbf to the cell locations (SEQ from the point layer -> CELL from the catch data) and output the 5 joined shapefiles.
  • Rasterize each of the joined shapefiles using the catch rate column (CR) for the value.
  • Resample the fisheries data to the same cellsize and extent and the productivty data
  • Grid algebra to adjust for productivity. The focalmean ensures that local variations in production are not as important as the average productivity of the general area. 
cw C:/WorkSpace/Global_Fisheries_NEW/normalized
w C:/WorkSpace/Global_Fisheries_NEW/normalized
grid

fishprod1 = (C:/WorkSpace/Global_Fisheries_NEW/resamp_rasters/fish1 * 907184.74) div 
            float(focalmean(C:/WorkSpace/ocean_primary_production/nibble/prodnib))
fishprod2 = (C:/WorkSpace/Global_Fisheries_NEW/resamp_rasters/fish2 * 907184.74) div 
            float(focalmean(C:/WorkSpace/ocean_primary_production/nibble/prodnib))
fishprod3 = (C:/WorkSpace/Global_Fisheries_NEW/resamp_rasters/fish3 * 907184.74) div 
            float(focalmean(C:/WorkSpace/ocean_primary_production/nibble/prodnib))
fishprod4 = (C:/WorkSpace/Global_Fisheries_NEW/resamp_rasters/fish4 * 907184.74) div 
            float(focalmean(C:/WorkSpace/ocean_primary_production/nibble/prodnib))
fishprod5 = (C:/WorkSpace/Global_Fisheries_NEW/resamp_rasters/fish5 * 907184.74) div 
            float(focalmean(C:/WorkSpace/ocean_primary_production/nibble/prodnib))


 The unit conversion factor ensures that the output grids ensure that the units are tons of fish catch per tons of carbon production annually.


units on fish catch: millions of tons fish / km^2 * 1km^2/ 1,000,000 m^2 = tons fish/ m^2

units on procuctivity: grams Carbon/ m^2 * 1 ton carbon/ 907184.74 g carbon  = tons carbon / 907184.74 m^2

fish catch / productivity : tons fish / m^2 * 907184.74 m^2 / tons carbon = tons fish / tons carbon







        


        

    
        
            
        
    


    
    


                    
                      
                 
    
        
    

                    

                  

                  

                



              
            		
            

            
            
            
          

        
      

      

      



      


      

        

        

      

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