Benthic Habitats and the Effects of Fishing

Symposium Abstract: A GIS Routine for Assessing Designs that Sample an Area of Fish or Lobster Traps

G. A. Matthews, R. L. Hill, and P. F. Sheridan

doi: https://doi.org/10.47886/9781888569605.ch126

Traps used in tropical fish and lobster fisheries may harm shallow reef habitats that have been identified as essential fish habitat for a number of federally managed species. We are evaluating the effects of these traps on benthic habitats in the Florida Keys, Puerto Rico, and the U.S. Virgin Islands by examining spatial distribution of traps and quantifying damage to structural benthos. ArcView is being used to organize and visualize the data and to choose some sampling parameters. An automated routine tests how well different transect widths represent the actual population density of traps among the area’s habitats. Custom scripts register the trap population density, the trap sample density by benthic habitat, and their cumulative differences. Trap locations (latitude and longitude) and benthic habitat polygons form the bases over which the user fits a rectangle to encompass the known trap population area. The user can then establish sub-rectangles of varying widths as ‘test-transects’ for sampling. A test-transect is stepped across the trap area in as many increments as desired up to a limit set by a required minimum 1-m offset distance. The number of traps in each transect is obtained, along with the density distribution among the benthic habitats. Using the cumulative differences in percentage distributions for habitats between test-transects and the trap population area, an optimal minimum transect width can be established to acceptably represent the distribution of traps among habitats. This will help focus underwater research on specific habitats (corals) where damage is most likely.