Marine

MRV Alba na Mara: survey 1215A programme

August 5, 2015 by Marine Scotland Communications No Comments | Category Marine Directorate Science, Research Vessel Surveys

• Duration: 12 – 28 August 2015

Gear:

• 60 mm prawn trawl BT 201
• 2 x Day grabs and 1 x sieving table
• Towed TV sledge, 600m umbilical towing cable and cameras (plus backup)
• TV drop frame (large version)
• Lasers and bracket for drop frame
• Prawn sorting table

 Objectives

• To obtain estimates of the distribution and abundance of Nephrops burrows in the Firth of Forth, and the Moray Firth using underwater cameras.
• To use the TV footage to record the occurrence of other benthic fauna and evidence of commercial trawling activity.
• To collect trawl caught samples of Nephrops for comparison of reproductive condition and morphometrics in each of the different survey areas.
• If time permits, deployments of the sledge and then the drop frame will be carried out on the same ground to compare Nephrops burrow density estimates obtained using the two different methods.

Procedure

Where possible, a random stratified approach will be adopted to investigate Nephrops burrow density in different regions of the study areas.

1. TV Observations: At each station a video camera mounted on the TV sledge will be towed across the seabed for approximately ten minutes at approximately one knot. Nephrops burrow abundance, other benthic fauna and signs of anthropogenic activity will be recorded on to DVD. Distance traveled by the sledge, the depth at which the sledge is at and camera height from the seabed will be monitored and recorded using a range finder mounted on the sledge.
2. Trawling: Fishing trawls of approximately 60 minutes duration will be made within each sediment type, within each survey area. A range of biological and morphometric data will be collected on Nephrops caught.
3. Drop Frame: The drop frame will be used where conditions are not suitable for using the TV sledge, recording similar data as to that of the TV sledge.
4.  Comparative work: Following on from work carried on previous surveys, on known Nephrops grounds the sledge will be towed along parallel tracks approximately 200 m in length (ten minutes towing time) and 100 m apart. Video footage and all observed data will be recorded as usual. Following this, the drop frame will then be drifted across the same area at 90^o to the sledge tracks. The frequency of this operation will depend on the weather and available time.

Further Information

• Marine Scotland Science
• Marine Scotland research vessels

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