Trawl-mounted video camera observations of snow crab interaction with footgear

Transcription

1 Trawl-mounted video camera observations of snow crab interaction with footgear Truong Nguyen 1, Paul Winger 1, George Legge 1, Earl Dawe 2, and Darrell Mullowney 2 1 Fisheries and Marine Institute, Memorial University 2 Fisheries and Oceans Canada

2 Purpose: Conduct trawl-mounted video camera observations of trawl footgear interacting with snow crab (including soft-shelled) on varying substrates. The goal was to provide insight into how individual crab interact with footgear components.

3 Materials and Methods:

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7 Start Start End End Depth (ftm) Tow No. Date Time Latitude Longitude Time Latitude Longitude Heading 1 June 19, : : June 19, : a a 09: a a June 19, : : June 19, : : June 19, : : June 19, : : June 20, : : June 20, : : June 20, : : June 20, : : June 20, : : June 21, : :26 b June 21, : : June 21, : : June 21, : :

8 Tow No. Camera Location Total Video (min)* Usable Video (min)** Comments 11 SD camera with 33% light (30 0 angle) was attached to fishing line of bosom section. 12 SD camera with 33% light (30 0 angle) was attached to fishing line of bosom section (as Tow 11) Light on camera caused reflection with suspended sediment in water. However, we were still able to examine a part of the bosom section. Two hard shelled crabs on GRID with no limb loss. One semi softshelled crab in pot with no limb loss Light on camera caused reflection with suspended sediment in water. However, we were still able to examine a part of bosom section. 13 SD camera with 33% light (30 0 angle) was mounted on the port side end of bosom section on fishing line. 14 SD camera with light off (30 0 angle) was mounted on fishing line of bosom section. Camera 2xLED with 100% was attached to headline pointing down to bosom section. 15 SD camera with 33 % light (30 0 angle) was mounted on fishing line of bosom section. Camera 2xLED with 66% was attached to headline pointing down to bosom section Light on camera caused reflection with suspended sediment in water. However, we were still able to examine a part of bosom section Fewer crab observed. No reflection with suspended sediment was found as in Tow It seemed to be easier to see footgear/crab interaction, but not really clearly as the turbid water Light on camera caused reflection with suspended sediment in water. However, we were still able to examine a part of bosom section.

9 Different Substrates Video Clip 1 Video Clip 2

10 Results: 1081 crab were observed

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12 Examples of snow crab in the mud

13 Examples of snow crab on the surface

14 180 Numbers of crab observed by size Small Large 0 Tow 11 Tow 12 Tow 13 Tow 14 Tow 15

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19 Video clip

20 Orientation of snow crab on or in the substrate relative to the centre of the footgear. Bars indicate percentage of individuals. The black line indicates the mean direction (193 ). A total of 1081 observations were included in the analysis. The Rayleigh test concluded that the orientation was non-random.

21 Direction of snow crab movement on the substrate relative to the centre of the footgear. Bars indicate percentage of individuals. The black line indicates the mean direction (1.85 ). A total of 938 observations were considered moving and included in the analysis. The Rayleigh test concluded that the direction of movement was non-random.

22 Other Interesting Observations? Images of Crab with Missing Limbs Interaction of the Shrimp Trawl with a Lost Crab Trap

23 Conclusions: Majority of crab were on the surface of the substrate. Majority of crabs were moving. 53% of crabs observed experienced a collision with the footgear (either disc or spacer/chain). Majority of collisions were less than 1 second. Majority of crabs passed under the footgear. Majority of crabs appeared to be aware of the footgear and are actively responding/reacting.

24 Recommendations: Conduct trawl modification to reduce impacts. Collect more video: - Other gear components (i.e. wires/doors or wing-sections). - Other substrates. - Higher crab densities. - Other footgear types (e.g. bobbin footgear).

25 He and Winger (2010)

26 Injury rates ranged between 3.3 and 10%, depending on the footgear type.

27 Ongoing Work: Two NL trawl manufacturers have been experimenting with seabed friendly versions of: 1) trawl footgear 2) semi-pelagic trawl doors. Flume tank experiments and preliminary field trials have been conducted. More field trials planned for this summer!!!

28 Funding Support Provided By:

29 THANK-YOU Paul Winger, PhD Centre for Sustainable Aquatic Resources Fisheries and Marine Institute of Memorial University of Newfoundland Web: