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Layer: Intensity (ID: 67)

Parent Layer: Non-Catch Shares Pot (2016-2017)

Name: Intensity

Display Field:

Type: Raster Layer

Geometry Type: null

Description: <DIV STYLE="text-align:Left;"><DIV><DIV><P><SPAN>This data layer depicts the relative intensity of fishing effort for commercial non-catch shares pot gear off the U.S. West Coast from 1 Jan 2016 to 31 Dec 2017. Records of pot gear fishing locations were compiled from one source: observer records from the West Coast Groundfish Observer Program (WCGOP) database. The WCGOP database includes records of trips for vessels participating in the following sectors: limited entry sablefish-endorsed primary season, limited entry non-sablefish endorsed, and open access fixed gear</SPAN><SPAN><SPAN>.</SPAN></SPAN><SPAN><SPAN>Annual WCGOP coverage of fixed gear sectors can be found online at: </SPAN></SPAN><SPAN><SPAN> </SPAN></SPAN><SPAN><SPAN>Because all fishing operations are not observed, neither the maps nor the data can be used to characterize the fishery completely. We urge caution when utilizing these data due to the complexity of groundfish management and fleet harvest dynamics.</SPAN></SPAN></P><P><SPAN>The intensity layer is a raster layer with cell values representing the total length of all lines intersecting a standardized area. To calculate this metric, we applied a line density algorithm in ArcGIS geographical information system software (Environmental System Research Institute, Incorporated, Redlands, California). The line density algorithm calculates density within a circular search area (radius = 5 km) centered at a grid cell (size 500 m x 500 m). The value (units: km/km</SPAN><SPAN><SPAN>2</SPAN></SPAN><SPAN>) for each raster cell is the quotient of total line portions intersecting the circular area per cell area. Since density outputs are highly sensitive to the specified radius and cell size, the absolute values are less important than the relative nature of them. The benefit of this output over depicting lines themselves is that the density output better identifies areas where fishing effort is concentrated, while still ensuring confidentiality of individual fishing locations. The initial density output was more spatially extensive than the one shown in the figures, because it included cells with density values calculated from tows made by less than three vessels. Those "confidential" cells were removed for the final published data layer. Density parameters were chosen in order to minimize data exclusion (due to confidentiality mandates) while still providing a fairly high spatial resolution (500 x 500 m).</SPAN></P><P><SPAN><SPAN>This spatial summary of fishing effort was developed from lines connecting gear set and retrieval points. Although fishing does not occur continuously along a fixed gear set (e.g., longline, pots), some amount of fishing does occur between set and retrieval points. For that reason, we treated fixed gear sets similarly to trawl tows. This summary is not intended to quantify total impact of fishing on either benthic or pelagic habitats.</SPAN></SPAN></P></DIV></DIV></DIV>

Copyright Text: Fishery Resource Analysis and Monitoring Division, Northwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration

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