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NEFSC/Industry Cooperative Survey Gear Study 28 October – 6 November, 2002 PowerPoint Presentation
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NEFSC/Industry Cooperative Survey Gear Study 28 October – 6 November, 2002. OBJECTIVE.

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slide1

NEFSC/Industry Cooperative Survey Gear Study

28 October – 6 November, 2002

OBJECTIVE

To examine differences in catch rates of the R/V Albatross IV using standard Yankee #36 trawls in two configurations; one configuration that conformed to standard specifications and a second configuration that was known not to meet specifications, including offset trawl warps.

Source Document: Specifications for Construction of NEFSC Standard #36 Bottom Trawl

slide2

SAMPLING AREAS

  • General sampling areas provided by industry
  • Specific areas determined onboard the ship

shallow - approximately 87 m (47.5 fm) in depth

mid-depth - approximately 139 m (76 fm)

deep - approximately 198 m (108 fm)

  • Areas selected in order to cover a range of depths and to sample
  • as many species as possible
  • Original plan was to sample 2 areas in 1 depth zone then 2 areas

in a second depth zone

  • Weather prevented occupation of 4 areas; therefore a third

‘shallow’ area was sampled

slide3

Area 2

100m

Area 1

Area 3

NEFSC/Industry Cooperative

Survey Gear Study – Part I

28 October – 6 November, 2002

Location of Sampling Areas

Closed Area I

slide4

BOTTOM PHOTO from NW CAI (Area 1)

Albatross Cruise 99-08, July 1998, Site I2

Image provided by Page Valentine, USGS, Woods Hole Field Center

slide5

BOTTOM PHOTO from NE CAI (Area 2)

Albatross Cruise 99-08, July 1998, Site I2

Image provided by Page Valentine, USGS, Woods Hole Field Center

slide6

STATION SELECTION

  • The areas were 5-minutes by 5-minutes (approximately 25 nm2)
  • Each area was subdivided into 25 blocks, each 1-minute by 1-minute
  • Each block was further subdivided into four quadrants
  • Sixteen blocks were chosen, the maximum possible number of
  • stations that could be performed during one 24 hour period,
  • using uniformly distributed random numbers
  • Stations were then placed in a randomly selected quadrant within
  • each block
slide7

4.75

4.25

3.75

3.25

2.75

2.25

1.75

1.25

0.75

0.25

GRID USED TO POSITION TOW STARTING POINTS

slide8

TOWING PROTOCOLS

  • Each area sampled for 48 hours
  • Order of gear configurations used determined by coin toss
  • One randomly chosen gear configuration was used for 24 hours,
  • then configurations switched and tows made at the same locations
  • the following day
  • Tows offset by approximately 1 additional hour to account for tide
  • and light conditions
  • Direction of tows determined by the Captain of the F/V Sea Breeze
  • Constant scope used for all tows within an area. Scope chosen
  • was that used for the deepest likely depth in an area
slide10

GEAR SPECIFICATIONS - R/V Albatross

‘Optimal’ (OPT)

  • Net #21, constructed prior to the experiment and inspected to meet
  • the specifications by industry representatives
  • Doors used (Pair #38) were inspected by industry representatives
  • to meet tuned door specifications
  • Backstraps used were fitted with swivels (with the appropriate
  • number of links removed to maintain standard specification) to
  • ensure that there were no twists in the chain while the net was
  • fishing
  • Even trawl warps; re-measured and certified the day of sailing
slide11

GEAR SPECIFICATIONS - R/V Albatross

‘Worst Case Scenario’ (WCS)

  • Net #14, used during the 24-27 October, 2002 ‘video cruise’
  • (the last 4 days of Leg II of AL 02-09, Autumn Bottom Trawl
  • Survey)
  • Pair #37 doors considered to be performing poorly during the
  • ‘video cruise’
  • Backstraps with no swivels and intentionally twisted 2 times
  • Trawl warps offset to match the mis-marked warps used during
  • 2001-2002 surveys
slide12

GEAR SPECIFICATIONS - F/V Sea Breeze

  • Standard 6" mesh groundfish net
  • 16” (with 12” at wings) rockhopper footrope with 2” cookies
  • 110' sweep
  • 30 fm groundcable used in Area 1
  • 50 fm groundcable used in Areas 2 and 3
  • 2.4” (6 cm) mesh codend liner
slide14

Albatross IV Tows

Sea Breeze Tows

Location of Paired Tows

Area 1: NW Closed Area I

‘Optimal’ Configuration

slide15

Albatross IV Tows

Sea Breeze Tows

Location of Paired Tows

Area 1: NW Closed Area I

‘Worst Case Scenario’ Configuration

slide16

Albatross IV Tows

Sea Breeze Tows

Location of Paired Tows

Area 1: NW Closed Area I

29-30 October, 2002

slide17

Albatross IV Tows

Sea Breeze Tows

Location of Paired Tows

Area 2: East of Cape Cod

‘Optimal’ Configuration

slide18

Albatross IV Tows

Sea Breeze Tows

Location of Paired Tows

Area 2: East of Cape Cod

‘Worst Case Scenario’ Configuration

slide19

Albatross IV Tows

Sea Breeze Tows

Location of Paired Tows

Area 2: NW Closed Area I

31 October-3 November, 2002

slide20

Albatross IV Tows

Sea Breeze Tows

Location of Paired Tows

Area 3: NE Closed Area I

‘Optimal’ Configuration

slide21

Albatross IV Tows

Sea Breeze Tows

Location of Paired Tows

Area 3; NE Closed Area I

‘Worst Case Scenario’ Configuration

slide22

Albatross IV Tows

Sea Breeze Tows

Location of Paired Tows

Area 3: NW Closed Area I

3-5 November, 2002

slide23

SAMPLING PROTOCOLS

  • Albatross
  • Catch sorted by species and weighed (nearest 0.001 kg) using
  • motion compensated digital scales
  • Lengths of all fish measured (nearest cm)
  • All catch and biological data were recorded using the shipboard
  • automated data entry system
  • Sea Breeze
  • Catch sorted by species and weighed using same scales
  • Individual fish lengths were taken on a subsample of the catch
  • when time allowed
  • Catch weights were recorded on standard fisheries observer program
  • logsheets and transmitted to the Albatross
  • Catch numbers and individual fish length data were also recorded on
  • fisheries observer program logsheets and processed at the Woods
  • Hole Laboratory the day after the cruise ended
slide24

SUMMARY OF TOWS CONDUCTED

IN EACH SAMPLING AREA