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What Happened?

What Happened?. Last week, inspection of Albatross IV’s trawl warps indicated inaccurate 50m markings Port and starboard warps fished at unequal length Mismatched length greater with depth Mis-marked cable used in winter 2000 through spring 2002 trawl surveys. What Have We Done?.

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What Happened?

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  1. What Happened? • Last week, inspection of Albatross IV’s trawl warps indicated inaccurate 50m markings • Port and starboard warps fished at unequal length • Mismatched length greater with depth • Mis-marked cable used in winter 2000 through spring 2002 trawl surveys

  2. What Have We Done? • Re-measured and remarked cable • Currently in use on fall 2002 trawl survey

  3. How Did It Happen? • We are still investigating the events • It appears that the cable was not marked at true 50 m intervals as it was wound on the cable winches in Feb 2000 • The cables are marked so the lead fisherman can tell how much cable is out • Marks are aligned to ensure that the port and starboard warps are the same length

  4. What Does it Mean? • At times, more cable was deployed on one side of the trawl than the other • The difference in length increased with the amount of cable out • Gear may have fished differently than previous surveys • Impacts on catch rates uncertain

  5. What was the difference between the warps? Percent of all tows Difference in warp lengths

  6. Will Advice on Stock Status be Affected? • We don’t know • We are currently examining the impact • We are examining our data and have planned additional analyses

  7. What Do We Know So Far? • Observed generally consistent trawls between NEFSC and other trawl surveys (Canadian DFO and inshore State of Massachusetts) for several species • Trawl mensuration experiments conducted in Spring 1996 (before current trawl warps installed) and Spring 2001 (after current trawl warps installed) • Differences in wingspread dynamics the same for both sets of experiments • Recent and current assessments diagnostics (residuals) do not indicate a change in catchability in the survey

  8. Planned Field Investigations • Underwater video work on tows with even and intentionally offset trawl warps to determine trawl configuration (next week) • Additional net mensuration work on tows with even and intentionally offset trawl warps (October 15-25, 2002) • Paired tows to compare catchability (Oct 15-25, 2002)

  9. Analyses of Information Already Collected • Conduct sensitivity analyses of VPA stock assessments (e.g. increase 2000-2002 survey indices by 10-50%) • Compare multispecies catch rates by depth from pair-wise surveys • Evaluate swept-area biomass estimates from surveys by depth to classify species most likely influenced by non-trivial differences in warp lengths

  10. Timelines Relative to Assessment Updates: • Groundfish Assessment Review Meeting (GARM) • October 8-11 – assessment meeting to update assessments • October 21 – GARM report finalized • Review of trawl warp analyses (data already collected) • Can be reviewed at GARM as separate term of reference • Review of data from 2002 autumn trawl survey as available (4th leg of trawl survey completed ca. October 25)

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