Report of the Study Group on Fecundity of Sole and Plaice in Sub Areas IV, VII, and VIII

2. INTRODUCTIONPopulation assessments based on fishery-dependent information have become less reliable over the last decade due to uncertainties about the actual level of commercial landings as well as their age-composition (Anon, 1992). The ICES North Sea Flatfish \Vorking Group, therefore, emphasized the need for fishery independent data sets on the trends in stock abundance such as bottom trawl surveys and egg surveys. Available Bottom Trawl surveys carried out annually to estimate the relative abundance of plaice and sole are (1) the UK ground fish survey which provides information on plaice since 1977; (2) the International Beam Trawl Survey which presents information on the abundance of sole and plaice in the southern North Sea (since 1985), eastern English Channel (since 1989), Bristol Channel and Irish Sea. These surveys can give an estimate of the abundance of the age-groups dominating the population, but may be less suitable to estimate the abundance of the older age-groups and thus of the total adult population. Abundance of the total adult population may be estimated from the total egg production through plankton surveys, providing an opportunity to validate the VPA.