Nephrops Under Water TV Surveys
Norway prawns (Nephrops norvegicus), also known as the Dublin Bay prawn, are common around the Irish coast. They are found in distinct sandy/muddy areas where the sediment is suitable for them to construct their burrows. Nephrops spend a great deal of time in their burrows and their emergence from these is related to time of year, light intensity and tidal strength. The Irish Nephrops fishery is extremely valuable with landings recently worth around €55m at first sale, supporting an important Irish fishing industry.
Purpose of Survey
Nephrops are managed in Functional Units (FUs). We have conducted under water television surveys since 2002 to independently estimate abundance, distribution and stock sizes of Nephrops norvegicus for:
- Irish Sea Nephrops Grounds (FU 14 and 15) in collaboration with AFBI an CEFAS.
- Porcupine Bank Nephrops Grounds (FU16)
- Aran, Galway Bay and Slyne Head Nephrops Grounds (FU17)
- South and South west Ireland Nephrops Grounds (FU19)
- Labadie, Jones and Cockburn Nephrops Grounds (FU20 and 21)
- “Smalls” Nephrops Grounds (FU22)
Each year during the summer months, on average 300 stations are surveyed each year, in three survey legs, covering all the FUs in depths from 20 to 650 metres.
Data are also collected on Nephrops behaviour, the impact of fishing activity on the seabed and benthic megafauna occurrence such as sea pens. Sea pen photograph guide for training is available here.
How Under Water TV Surveys Work
A high definition camera system is towed over the sea bed for 10 minutes travelling approx. 200m at 0.8 knots on a purpose built sledge. The Nephrops burrows in the seabed are annotated by experienced scientists using an inhouse developed review app. The burrow density estimates are then calculated up to the entire area of the Nephrops grounds using geo-statistical methods. The UWTV survey follows survey protocols available here agreed by International Council for the Exploration of the Sea (ICES) Working Group on Nephrops surveys (WGNEPS).
View 'A guide to Nephrops burrow identification'.
Photo of UWTV sledge on the deck of RV. Tom Crean during the Porcupine Survey
How We Review UWTV Images
Image-annotation-R-Shiny-app was developed in-house to review the images so we can annotate the Nephrops burrows, log presence / absence data for benthic megafauna. The code for the app is here.
A video clip demonstration of UWTV review app can be viewed below.
Recent Survey Results
Results of these surveys are submitted to annual ICES Working Group for the Celtic Seas Ecoregion (WGCSE) for the provision of catch advice for the next fishing year.
Survey summaries are also presented in the context of the other Nephrops UWTV surveys across the survey network in the annual WGNEPS reports. These include recent trends, density (burrow/ m²) maps and technology advances.
Annual UWTV Survey reports for each Marine Institute survey can be downloaded from the open access repository.
Areas Covered during our Nephrops UWTV Surveys
In the map above, the blue dots illustrate the stations positions surveyed by the Nephrops Under Water TV Surveys on each of the Nephrops grounds. The functional units (FU) are numbered 14 to 22, and shaded in different colours.
The Nephrops Under Water TV Surveys are part of Ireland's Data Collection Scheme which is carried out under Ireland's Operational Programme (OP), co-funded by the European Maritime, Fisheries and Aquaculture Fund (EMFAF) and by the Irish Government.