Marine

MRV Alba na Mara: Survey 0316A Programme

March 4, 2016 by Marine Directorate Communications No Comments | Category Compliance, Marine Directorate general, Marine Directorate Science, Marine Litter, Research Vessel Surveys

Duration: 7-21 March 2016

Equipment:

• BT 201 Prawn net – rigged with separator grid and two 80 mm codends
• Trawl doors
• Sweeps, bridles, backstrops and pennants
• Spare netting and twine
• Live capture codends
• PSL5000 light unit x 2
• 4 x 10m side emitting light cables
• Battery pods
• Video Cameras
• Flashback recorders and housing
• Pyramid camera frames
• TechnoSmart AXY tilt sensor
• Scanmar units – wing, door, height and depth
• Catch bins
• Catch sorting table

Objectives:

• Investigate whether light influences fish behaviour in the extension of the trawl.
• Obtain video footage of the separator lighting grid.
• If time permits at the end of the cruise, carry out live capture of haddock for fish behaviour work back at the lab.

Procedure
Equipment will be loaded onto MRV Alba na Mara at Fraserburgh on 4 March 2016, where the trawl will be rigged onto the net drum.  Scientific staff will join Alba on the evening of 6 March, then leave harbour and steam to fishing grounds approximately 9nm east of Aberdeen to commence work on 7 March.  A number of short hauls will be carried out to ensure the separator grid in the trawl is rigged correctly through observations with video cameras mounted on the trawl and analysis of a tilt sensor mounted on the grid.  After the rigging trials are complete fish behaviour trials will commence.  If sufficient valid fish behaviour hauls are completed during the survey, then some time at the end of the trip will be used for live fish capture.  Alba will return to Fraserburgh on the evening of 20 March to unload equipment and scientific personnel on 21March.

Fish Behaviour Trials
The BT201 prawn trawl is fitted with a horizontal separator grid in the extension that leads to two separate 80 mm codends.  There will be two light fibre lines permanently attached to the grid, one illuminating the upper half and one illuminating the lower half of the grid.  This will allow four lighting variables to be trialled: upper light on, lower light on, both lights on and both lights off.  The lighting variable will be changed between hauls so that each gets an even distribution of the working period throughout the survey.  The PSL5000 light unit and 12V battery pack cannot be wound onto the net drum so will be attached to/detached from each light fibre cable during shooting/hauling as required.

The working hours during the survey will be midday to midnight.  This is to allow hauls to be conducted in daylight and dark conditions.  Around four or five fishing hauls will be carried out each day, with the aim of achieving at least two light and two dark hauls per day.  Hauls will be 45 minutes long initially, with the potential to be adjusted depending on the catch volume.  The net will be towed at three knots.  Scanmar units will be used to monitor wing spread, door spread, and headline height and depth during each haul.

Large bins will be used on deck to receive and store the catch from the separate codends.  The catch will be sorted into key species, weighed and individual total length measurements recorded.

Live Fish Capture
The separator grid and twin codends will be replaced with the live capture codend.  The tows will last 20 minutes and the net will be hauled back slowly.  The catch will be sorted on-board with healthy haddock in good condition being placed in tanks of aerated seawater.  The fish will be handed over to MSS aquarium personnel once in harbour for transporting back to the marine lab.

Marine Litter
Any marine litter brought onboard during trawling operations will be documented before being placed into “KIMO Fishing for Litter” bags.  At the end of the survey the bags will be deposited safely on the quayside to be collected for disposal.

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