Evaluating Sponge Encounter Thresholds through GIS Simulation of the Commercial Groundfish Fishery in the NAFO Regulatory Area

This report utilizes a geographic information systems (GIS) modelling approach to simulate commercial groundfish trawling sponge by-catch in lieu of actual commercial observations within the confines of current management restrictions to fishing within the Northwest Atlantic Fisheries Organization Regulatory Area (e.g., coral and sponge closed areas). Simulated trawl start locations (1500) were generated by using an aggregated 2008-2009 groundfishing effort raster asa probability surface. This effort surface was also used toset a heading for each of the lines following the direction corresponding to the maximum sum of effort. Combined and standardized sponge bycatch data from the Spanish and Canadian research vesseltrawls were used to create a by-catch sponge biomass surface. The model extracted the spongebiomass values to each line to calculate the total by-catch per line (kg). Artificially imposing a range of threshold values on simulated by-catch data showed very few simulated trawls (0.4%) would catch more than the 800 kg encounter threshold of sponge under current management conditions. The percentage of simulated trawls above the imposed range ofthreshold values does not start to increase quickly until the threshold was between ~30 and 50 kg. At 50kg of simulated by-catch, only 5.5% of simulated tows would be affected and could be easily avoided as the areas impacted are localized. If the current encounter threshold for sponges was reduced from 800 kg to between 30 and 50 kg per tow it is unlikely to have a large effect on the commercial fishery within the fishing footprint and would serve as a more effective sponge conservation measure in un-fished areas under an exploratory fishery.Versión de edito