What Happened?

1
What Happened?

• Last week, inspection of Albatross IVs 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 dont 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)