North Sea young fish survey (August - September)

Area

Inshore coastal waters of the Central and Southern North Sea (ICES Divisions IVb and IVc), between (a) the River Humber to the north Norfolk coast and (b) the Greater Thames Estuary.

Young fish survey Fig. A Young fish survey Fig. B

Objectives

To provide indices of abundance of small dermeral fish, in particular juvenile 0-group and 1-group plaice and sole, prior to their recruitment to the fishery. The data is in support of the EU Data Collection Regulation.

History

Studies in the early 1960s of coastal waters around England and Wales have shown their importance as inshore flatfish nursery grounds, in particular for plaice and sole. More extensive surveys were undertaken during the 1970s to evaluate the extent of these populations and from 1981 onwards the survey was conducted annually. The extent of the area covered by the survey has changed over this period and has been more extensive than the present study area. The survey once covered the English coastline from Flamborough Head on the northeast coast to Portland Bill on the south coast, as well as Morecambe Bay for a short while. In addition to the 2 metre beam that is used presently, a 1.5 metre push-net, designed to have similar efficiency and selectivity, was operated at the low water mark in water depths less than 1 m. The use of the push-net ceased in 1999.

The vessel and the gear

Small inshore vessels are chartered for the survey. Fishing is conducted during daylight hours and a 2 metre wooden beam trawl, rigged with three tickler chains and a 4 mm mesh liner, is towed with the tide for a duration of ten minutes covering a distance of around 450 m.

Survey design

The survey is carried out by two teams of scientific staff, one surveying the area between the River Humber to the north Norfolk coast and the other, the Greater Thames Estuary. For the survey the coast is divided into sectors, referred to as mini areas, which are based on geographic features, and within these a 161 fixed prime stations are fished annually between late August and early September. This is the period when the majority of newly metamorphosed fish occupy shallow nursery grounds in high numbers. Furthermore each fixed station is permanently assigned to a stratum based on the chart depth. At each station all finfish species are measured, the commercial shellfish species quantified and the epi-benthic species counted at some of the fixed prime stations. Environmental observations are also made and otoliths collected from plaice and sole for age determination purposes.