October 6, 2015
by Lyndsay Cruickshank
Duration: 5-16 October 2015
- Midwater trawl PT160 x 2
- Edgetech broadband towed system
- Seabird 911 CTD
- Go-pro camera system(s) with additional sensors (depth, temp, attitude etc)
- Towed hydrophone array
- Lowrance echosounder system
- Simrad WBAT autonomous broad band sounder system
- Rod and line systems.
- Electronic load shackle for weighing catch.
- Scanmar trawl eye sensor.
- To estimate mackerel density and abundance in the area of the Shetland Isles
- To investigate the use of a broadband system as a means to determine mackerel size
- To study distribution of cetaceans and their relationship to mackerel shoals.
- Calibration of Edgetech Broadband system.
- Calibrate Sv and TS gains on the Simrad EK60.
- Obtain acoustic data from mackerel using the Edgetech broadband system.
- Obtain biological samples of mackerel from schools by trawling.
- Trial deployment options for the Edgetech broadband system.
- Obtain acoustic data from mackerel using the Simrad WBAT autonomous broadband system.
- Compare the echo returns from a low cost portable sounder system with those from the calibrated Simrad EK60 echo-sounder system.
- Deploy a lightweight AU Go-Pro camera system into the mackerel schools to observe behaviour.
- Deploy MSS Go-Pro system on PT160 net
- Deploy MSS Go-Pro lander system onto the sea bed to identify fish traces on un-trawlable ground.
- Visually observe marine mammal distribution and activity during daylight hours.
- Obtain towed hydrophone acoustic recordings of mammal vocalisation during survey transects.
- Compare netsonde traces of mackerel in the net with those seen using the cable less Scanmar trawl eye system.
All gear will be loaded inAberdeenon 2 October. The vessel will departAberdeenon 5 October and make passage for Loch Erribol, where a calibration of all drop keel mounted acoustic transducers will take place (approximately 8-12 hours at anchor). Crew training and trial deployments of fishing gear will take place en route to the calibration site as convenient for the fishing master. (Note that weather conditions may preclude this activity, in which case the survey transects will commence with acoustic calibrations taking place when conditions are suitable).
In addition, during calibration, an investigation of the acoustic output of the broadband system will be attempted using a standard target below the suspended towed body. In the event that there is insufficient depth for this exercise in the selected anchorage this may be done later in the open sea with the vessel drifting if weather conditions allow. Time period for the broadband system investigation is likely to be six to eight hours.
Scotia will make her way to the survey area after the calibration has been completed. The proposed survey area and possible survey track is shown in Figure 1. However, this is based on the expected position of the Scottish pelagic fleet which will be fishing for mackerel at this time. Contact will be maintained with the commercial fleet using email, cell phone and radio communication and the survey area/design may be altered to reflect any changes in the fish distribution. The survey design will consist of a combination of parallel transects running east/west, or zig-zags into and out from the coast at normal steaming speed (approximately 10.5 knots). When areas of suitable shoals are encountered work using the broadband system will then be concentrated in that area.
A small boat transfer or short port call may be made, as convenient, after 9 October to allow A Fenwick off the vessel. This is likely to be from Scalloway or Lerwick depending on the progress of the survey and position of the mackerel schools. Note this will not be a 24 hour port call.
Acoustic data will be collected at four frequencies (18, 38, 120 and 200 kHz) on a 24 hour basis. While transecting, a towed hydrophone array will be deployed over the stern of the vessel and will be recovered prior to any fishing operations. The towed hydrophone will not restrict the vessels movement when at survey speed.
Fish schools seen on the echosounder will be identified using a pelagic trawl (PT160). Trawling operations will be carried out at any time in a pre agreed period, probably between 09:00 and 21:00 hours. The vessels netsonde systems will be required to monitor catch density and position of schools in the water column during trawling. The SH80 sonar will be used to collect acoustic data and direct trawling operations.
Biological sampling of all species caught will be carried out as per standard sampling protocol with 5 otoliths per cm length for each haul plus required length and weight data.
A vertical CTD dip will be carried out immediately following a pelagic trawl or once a day if trawling has not taken place, this will require the vessel to use its DP system to remain on station.
Deployment into mackerel schools of the fishing rod mounted Go-Pro camera/sensor system will be done either from the hanger deck in DP or with vessel drifting depending on the conditions. The opportunity will be taken during some tows to deploy the MSS net mounted Go-Pro system on the net.
Go pro systems may be deployed onto the seabed if schools are seen in un-trawlable areas.
The ships thermo-salinograph will be run continuously to obtain sea surface temperature and salinity throughout the survey area.
Figure 1: Provisional Survey track 1415S.