A Geographic Information System (GIS) simulation model was developed to assess management decisions pertaining to commercial sponge by-catch by the Greenland halibut fishery in the Northwest Atlantic Fisheries Organization (NAFO) Regulatory Area (NRA). Sponge biomass by-catch from research vessel stratified random surveys was interpolated using an inverse distance weighted (IDW) algorithm to produce a smoothed surface. Data on fishing effort were interpolated using a kriging procedure and were used to weight both start positions of simulated trawls, as well as trawl direction. These weighted positions (Model B) were contrasted with randomly placed start positions with random trawl direction (Model A). In order to evaluate the effect of area closures put in place by NAFO on the simulated sponge by-catch, Models A and B were each run iteratively under two scenarios: 1) simulated trawl lines within the fishing footprint, and 2) simulated trawl lines within the fishing footprint and outside of the closure areas. For each of the four outcomes, 1500 simulated sponge by-catch weights were used to evaluate the effect of spatial closures and an 800 kg encounter threshold for commercial catches. The model suggests that the current area closures to protect coral and sponge grounds will have reduced sponge by-catch by 28% if fishing effort was distributed as it had been for the previous 20 years. It also estimated that 8.5% of the by-catch records were over 800 kg, with most of these found adjacent to the Sackville Spur sponge closure or the Flemish Pass area closure, and along the canyon heads of the Grand Banks. The model indicates that reducing the encounter threshold from 800 kg to 100 kg/37 km tow would only affect a further 8% of the simulated by-catch records and protect sponges at the canyon heads of the Grand Banks and in the slope waters of Flemish Pass.
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