Irish Sea and Bristol Channel survey (September - October)

Area

ICES Divisions VIIa and f. If time allows some survey positions in VIIg. Irish Sea, Bristol Channel and St Georges Channel.

Objectives

To provide indices of abundance which are independent of commercial fisheries of all age groups of sole and plaice in the Irish Sea and Bristol Channel grounds for ICES Working Groups (Northern and Southern Shelf), and an index of recruitment of young plaice and sole prior to full recruitment to the fishery.

History

An autumn Irish Sea groundfish survey has been carried out annually by MAFF/Defra since 1979. A Granton otter trawl was used until 1987, then in 1988 the commercial 4m beam trawl that is currently used was introduced. At the same time, a limited beam trawl survey was carried out in the Bristol Channel. From 1988 to 1992 the main survey effort was concentrated in the north-east Irish Sea and the Bristol Channel, and since 1993 a standard survey covering the whole of ICES Divisions VIIa and f has been undertaken, with additional tows in the Northeast of ICES Division VIIg fished when time allowed. This survey provides commercially independent abundance and recruitment data used in the Northern and Southern Shelf Demersal Working Groups.

Vessel and gear

The sampling gear consists of commercially rigged (1989 style) 4m beam trawl (measured between inside edges of shoes) fitted with a chain mat, flip-up ropes, and a 40mm cod-end liner. The gear is towed at 4 knots (ground speed) for 30 minutes on a warp length appropriate to the depth of water (on RV Corystes a ratio of between 3.5 and 4.0). Fishing is only carried out in daylight on this survey, as catch rates can be very different in the dark under certain conditions. To date there have been no rigid guidelines to determining dark, but we usually aim to have the catch on deck within about 30 minutes of sundown. All stations are identified by unique prime station numbers that never change irrespective of the survey station number. There is no particular order in which the stations are worked, although attention is paid to the historical calendar period. If static gear or other restrictions prevent the execution of a primary station there are often alternative tows in the same area.

Survey design

The standard survey has a total of 97 tows of 30 minutes duration (Primary stations), with 65 in VIIa and 32 in VIIf. Station positions are fixed and can be identified by a unique prime station number. These stations are stratified by sector and depth-band. Primary survey stations total 34 in the eastern Irish Sea (ISN+ISS), 15 in the western Irish Sea (ISW), 16 in St Georges Channel (SGC), 32 in the inner Bristol Channel (BCI), 11 in the outer Bristol Channel (BCO), and 11 in the Celtic Sea (SEI). The 67 stations in sectors ISN, ISS and BCI are given top priority as they contribute to the VPA tuning and recruitment indices at the respective Working Groups. Three depth bands were used until 2000: 0-20m, 20-40m and 40+m; in 2001 these were reduced to 2 depth bands: 0-20m and 20+m.

Results

Current survey results can be mapped by ICES rectangle from iSEA - interactive Spatial Explorer and Administrator