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?

• Re-measured and remarked cable

• Currently in use on fall 2002 trawl survey

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

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

0

3

6

9

12

0 100 200

Approximate Fishing Depth (m)

War

p L

engt

h D

iffe

ren

tial

(ft

)

0

25

50

75

100

Cu

mm

ula

tive

Fre

qu

ency

D

istr

ibu

tion

of

Tow

s

What was the difference between the warps?

Percent of all tows

Difference in warplengths

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

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

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)

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

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)