Name: Biomass_Hotspot_Invert_Trawl

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Description: Data source:DFO synoptic groundfish trawl surveysMethods summary:Invertebrate biomass was calculated from CPUE (kg/hr) from DFO groundfish synoptic bottom trawl surveys that are carried out at depths of 50–1300 m. DFO synoptic surveys are standardized, depth-stratified random bottom trawl surveys in four regions of BC that cover the continental shelf of BC: West Coast Haida Gwaii, Hecate Strait, Queen Charlotte Sound, and West Coast Vancouver Island. These surveys do not include inlets, enclosed waters, sensitive habitats (e.g., Hecate Strait Glass Sponge reefs, Learmonth Bank Red Tree corals, Rockfish Conservation Areas), areas that are not trawlable or the steep slope off the southwest part of Haida Gwaii (Workman et al. 2008, Olsen et al. 2009). All species caught are weighed or counted and identified to the lowest possible taxonomic level. Data was extracted from DFO's GFBio database on 28 November 2016, limiting the query to records quality-tagged as "fully usable". The synoptic dataset spans July 2003 - June 2016, and includes samples from the months of May to October, but most are from May to July. Total biomass was calculated from the sum of CPUE fromall invertebrate taxa within each fishing event (trawl tow).Biomass values were used to detect hotspots of invertebrate biomass within shelf areas using the Getis-Ord G* tool. The G* statistic represents the local neighbourhood sum compared proportionally to the sum of all features in the study area. When the local sum is significantly different from the expected sum, then that site is identified as a hotspot (Gi_Bin>0), a cold spot (Gi_Bin<0), or neutral (Gi_Bin=0). A 10 km distance value was used as the neighbourhood size. The false discovery rate correction was applied, which accounts for multiple testing and spatial dependence. Absolute Gi_Bin values of 1, 2, and 3 correspond to 90, 95, and 99% confidence, respectively. Using the Minimum Bounding Geometry Tool, convex hull polygons were drawn around groups of hotspot points (confidence ≥90%) containing 10 or more points. The resulting polygons were then buffered by 1 km and manually edited where needed to exclude any large areas of the polygons that did not include hotspot points.This layer was reviewed as part of a Canadian Science Advisory Secretariat (CSAS) regional peer review process on Nov 1-2, 2017 (Rubidge et al. 2018).Date Represented: 2003-2016Date Updated: Nov 2017References:Olsen, N., Rutherford, K.L., Stanley, R.D., and Wyeth, M. 2009. West Coast Vancouver Island Groundfish Bottom Trawl Survey, May 26th to June 22nd, 2008. Can. Man. Rep. Fish. Aquat. Sci. 2092: 50 pRubidge, E., Nephin, J., Gale, K.S.P., and Curtis, J. 2018. Reassessment of the Ecologically and Biologically Significant Areas (EBSAs) in the Pacific Northern Shelf Bioregion. DFO Can. Sci. Advis. Sec. Res. Doc. 2018/053. xii + 97 p.Workman, G.D., Stanley, R.D., Olsen, N., and Rutherford, K.L. 2008. West Coast Queen Charlotte Islands Groundfish Bottom Trawl Survey, September 11th to October 17th, 2007. Can. Man. Rep. Fish. Aquat. Sci. 2823: 45 p.

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