July 2, 2015
by Lyndsay Cruickshank
Duration: 3-22 June 2015
- 2 x ScotiaBT175 80mm prawn trawls
- 2 x Day grabs and 1 x sieving table
- Towed UWTV sledge
- 2 x 600m umbilical towing cables and associated TV equipment (including back up).
- To obtain estimates of the abundance and distribution of Nephrops burrow complexes at Fladen, in the North Minch, theSouth Minch, the Firth of Clyde, in the Sound of Jura and at Devil’s Hole. If time and weather permits, stations at the Noup may also be surveyed;
- To use the TV footage to record the occurrence of other benthic fauna as well as evidence of commercial trawl activity;
- To collect sediment samples at each station;
- To carry out trawling for Nephrops, based on one haul in each sediment stratum in each of the main survey areas, to obtain samples of Nephrops for size composition analysis;
- To collect samples of Nephrops from the trawls for comparison of reproductive condition and morphometrics in each of the different survey areas (functional units);
- To record and retain marine litter obtained from trawling as part of the MSFD.
The main areas in which the survey will take place have been surveyed on annual basis for a number of years and are shown in Figure 1. A combination of two approaches will be used to derive the survey positions: a stratified random approach and fixed stations. The majority of stations will be generated by employing the traditional stratified random technique based on sediment distribution in all areas except the North Minch, where stations will be randomly generated within the boundaries of commercial Nephrops fishing effort, obtained from the Vessel Monitoring System. Alternatively at the Devils Hole and within some of the other survey areas there are a number of fixed stations. The location of all TV stations will be provided ahead of the cruise.
Weather permitting, it is planned that the vessel will first carry out a training session in deploying the sledge en route to the Fladen grounds. Initially approximately 450 m of the TV cable will be paid out with a large buoy (supplied by MSS) attached to the end of the cable to be lowered into the water. This will add back tension to the cable on recovery. The sledge will then be attached to the umbilical, and as a training session, the sledge will be shot and recovered. When this procedure is completed to the satisfaction of all involved, the vessel will then progress on to the first of the Nephrops burrow TV stations at the SW edge of the Fladen ground. Once the work at Fladen has been completed, the vessel will then steam around to the west coast and survey stations in the North andSouth Minches.
It is anticipated that the vessel will work south along the western side of the minches towards theClyde, surveying TV sites and carrying out trawls as required. The timing of the half landing will depend on how well the work has progressed and berth availability at Campbeltown, but it is anticipated that theClydewill be surveyed before the half landing; although this can be reviewed nearer the time and adjustments made accordingly. There are no fixed commitments to when the half landing takes place and there will be no exchange of MSS staff when tied up in port.
Following the half landing the survey will continue in the Sound of Jura, followed by the remaining South andNorth Minchstations whilst working north. If time and weather permits, a small number of stations at the Noup may be attempted before heading east. Any additional stations in Fladen (if required), or those not covered on the first leg of the survey, will be completed before heading to the final survey area at the Devils Hole.
When on station, sledge deployments and TV observations will be carried out 24 hours a day. There will be three teams of two staff, each working eight hour shifts and all will be involved in deploying and recovering the TV equipment, recording data and liaising with the ship’s compliment. There will be a requirement for staff to work outwith their shift period, which will include reviewing video footage, assisting in working up trawl catches and data entry. All work will be carried out in accordance with WTR regulations. The names of staff on each shift, watch leaders and the shift patterns will be provided to the ship prior to sailing.
At each TV station a video camera mounted on to the sledge will be towed along the seabed for approximately 10 minutes at approximately 1 knot and in to the tide – the ship’s dynamic positioning will be required for this. Observed Nephrops burrows, individual Nephrops and other benthic fauna will be recorded onto DVD for analysis. The depth and distance travelled by the sledge, as well as camera height from the sea bed, will be recorded automatically. Where practical sediment samples will be taken using the mini van Veen grab mounted on the sledge. However it may be necessary to use the Day Grab on occasion, if the mini van Veen fails. All sediment samples will be frozen.
Trawl caught samples of Nephrops will be collected and information on size composition, maturity and morphometrics will be recorded. Up to five trawls may be made in Fladen with a maximum of three tows in each of the other survey areas. Trawls will be carried out over different sediment types as defined by BGS. Trawls will be no longer than one hour long and carried out at either dawn or dusk. Any litter collected in the trawl will be recorded as set out in the SOP and placed in bags to be disposed of on return to port. There will be a requirement for the trawl to be cleaned by ‘streaming’ it behind the vessel for 15 minutes between the main fishing areas, as well as a final, more prolonged clean at the end of the survey.