Report of the Workshop on Trawl Warp Effects on Fishing Gear Performance, Marine Biological Laboratory, Woods Hole, Massachusetts, October 2-3, 2002
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Report of the Workshop on Trawl Warp Effects on Fishing Gear Performance, Marine Biological Laboratory, Woods Hole, Massachusetts, October 2-3, 2002

Filetype[PDF-3.58 MB]


  • Description:
    "On 3 September 2002, in response to a concern raised by a member of the fishing industry, the trawl cables ('warps') on the NOAA Ship ALBATROSS IV were inspected and found to have inaccurate 50-meter markings. That is, the marks were not exactly at true 50-meter intervals over the first 1,000 meters of the warps. The difference in marks from the true values ranged between less than 1 inch to 38.4 inches. Also, some of the marks were not evenly matched between the port and starboard cables. The cables were mismarked by the vendor upon installation in February 2000 and were used in eight bottom trawl surveys beginning with Winter 2000 and ending with Spring 2002. Thus, at times during these surveys, more cable may have been deployed on one side of the bottom trawl than on the other. The difference between the two warps is a matter of inches at shallower fishing depths but increases as more cable is set out. For example, when 100 meters (328 feet) of cable are deployed, the warp lengths differ by about 1 inch; when 300 meters (984 feet) are let out, the warp lengths differ by about 6 feet. Approximately 75% of the sampling tows accomplished in the bottom trawl surveys use 300 meters or less of cable. Due to the warp offsets, the survey trawl gear may have fished differently during the eight bottom surveys than during previous surveys, and this may have affected survey catch rates and related survey data used in stock assessments. To evaluate the possible impacts of the warp offsets, data from the last two year's of surveys are being reanalyzed by species, geographic area and depth to detect any changes in catchability that may have occurred . Additionally, the survey results are being compared to the results from other trawl surveys (e.g., Canadian Georges Bank bottom trawl surveys; NMFS sea scallop surveys) conducted during the winter 2000-spring 2002 time period. The sensitivity of groundfish stock assessment results to possible changes in survey catch per tow indices that may have been induced by the warp offsets is also being examined by arbitrarily increasing the catches in the eight surveys by 10%, 25% and 100%, redoing the assessments and then determining the improvement, if any, in the fits of the assessment models. All of the above analyses will be summarized in the Report of the Groundfish Assessment Review Meeting (GARM) that will be available and distributed at the end of October 2002."--Introduction.
  • Content Notes:
    "October 2002."

    "Web version posted October 25, 2002."

    System requirements: Adobe Acrobat Reader.

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