Irish Ground Fish Survey for commercial fish species

The dataset includes age- and length-based catch per unit effort data for commercial fish species collected during the Irish Ground Fish trawl survey.
Fisheries Science Services (FSS) carries out the annual Irish Groundfish Survey (IGFS) in the fourth quarter of each year as part of a larger coordinated survey effort with our EU neighbours (France to the south; and the UK to the north). 

A broad spectrum of data is collected during the survey, but the overriding objective is to provide information on commercially exploited fish stocks. In particular the survey provides an index of the proportion of juveniles in the stock, which in turn gives an indication of its spawning success. This is an important source of information not available from commercial landings due to the necessary minimum fish length restrictions on commercial catches. 

In addition, the survey provides data on species and environmental parameters in areas of both high and low commercial activity. This gives a better context to data for the entire survey area as opposed to focusing entirely on traditional fishing hot-spots that can remain stable while significant changes in surrounding background abundance and distribution go un-noticed.

The primary goal of the groundfish survey is to develop estimates of juvenile abundance for important species. Measurements of the abundance of juvenile fish are a critical measure of the health of a stock, serving as an annual indication of recruitment (the number of newly spawned fish which enter the population each year) success or failure. Most importantly, they allow forecasting of future commercial abundance. 

Survey provides data on the distribution and biology of commercial and non-commercial species of ecological interest, as well as hydrographic and environmental observations. When these data are combined with annual recruitment indices they can help identify the possible causes driving year-class success or failure, and allow us to see long-term changes in populations that may have been caused by fishing, pollution, or climate change. This spatial dataset comprises the haul station location from the trawl survey. The Irish Groundfish Survey feeds into the International Bottom Trawl Survey [ie. IBTS] for international reporting. 

The Irish West Coast Groundfish Survey started in 1990 and for the first two years consisted of circa 25 stations concentrated around the Irish coast in ICES Areas Via South and VIIb. Adverse weather in 1992 limited station coverage to only 4 stations which effectively broke the time series.

The survey was re-established in 1993 and has consisted of circa 70 stations, for Parts A and B combined, since then. Spatial coverage was extended west out to the 200m contour, but remains as Via South and VIIb.

Due to the restrictions of the current and previous research vessel commercial trawlers have been contracted to carry out the survey work. Wherever possible continuity of vessel and gear has been maintained and standard IBTS methodology applied. However, due to reduced staffing on commercial vessels it has rarely been possible to completely sort the catch.

Until 2000 all cod were sorted from the catch and then a sub-sample of two baskets was taken and completely sorted. From 2001 onwards, in response to an overall review of survey sampling undertaken during the IPROSTS Project (Anon 2001), the catch is completely sorted for all target species and a qualitative assessment made of the residual catch as a minimum.

The Irish surveys use an ICES rectangle based sampling strategy. The sampling design attempts to allocate at least two stations per rectangle (where the sea area is appropriate). Stations are selected randomly within each rectangle from known clear tow positions.

On the WCGS and ISCGS circa 70 fishing stations are planned on each survey every year. The number of hauls is adjusted according to the ship time available at sea.

The Irish West Coast Groundfish Survey is carried out in two parts: Part A covers ICES Division Via (south) and VIIb (north); Part B covers ICES Division VIIb and VIIj. The survey is conducted from 15 to 300 m depths during the fourth quarter (October - November). The Irish West Coast Groundfish Survey is carried out on chartered commercial fishing vessels. Whilst the same vessel (MFV Marliona, 224 gross tonnage and 30 m LOA) has normally been used each year for Part A and Sionann for Part B, in 2001 Part B was conducted from the MFV Regina Ponti (34.5 m LOA). Both vessels use a Rockhopper net with 12 inch discs and 11 inch Thyboron doors. The nets are fitted with a 20 mm codend liner. Gear performance throughout the survey is monitored using Furuno Ch24 (Headline Monitor).

The Irish Sea Celtic Ground Survey commenced in 1997 and evolved from an earlier Irish Sea Juvenile Fish Survey. As a consequence early survey stations concentrated largely, though not exclusively, around a number of shallow spawning areas along the Irish east coast in VIIa. These positions were expanded in combination with clear tows provided by the industry and CEFAS as well as some exploratory tows.

Spatial coverage therefore extended into the western Irish Sea from 2001 into the area around the Isle of Man, Liverpool and Cardigan Bays and the Welsh coast. The survey is carried out on the Irish research vessel the R.V. Celtic Voyager.

The sampling procedure on board conforms to the IBTS standard protocols and as such all cod are sampled and aged, the entire catch is sorted and then sub-sampled as and where appropriate.

The Irish survey in the Irish Sea and Celtic Sea covers ICES Division VIIa and VIIg. The survey is conducted from 10 to 150 m depths during the fourth quarter (November-December) by the RV Celtic Voyager. This vessel is 32 m in length with gross tonnage of 340 t. The fishing gear used is a GOV 28.9/37.1 Trawl with Morgere Kite (0.85 by 0.85m). Mean vertical opening is 6 m and door spread 48 m. Morgere Polyvalent doors (Type AA4.5) are used and gear performance is monitored throughout the survey using the SCANMAR (RX400) net monitoring system (Headline height, Door spread).

Trials on the new 65m research vessel, the R.V. Celtic Explorer, are due to commence in late 2002. Therefore, from 2003 onwards all Irish Surveys will be conducted on this new vessel, starting around mid October through to late November.