Nephrops norvegicus, commonly known as Noiway lobster or Dublin Bay prawn, is a commercially exploited benthic decapod crustacean widely distributed across the continental shelf of the northeastern Atlantic Ocean. Du.ring its life cycle, the species undergoes a planktonic larval phase, which includes three zoeal stages and lasts approximately 45 to 50 days, in total. The third zoeal stage is followed by metamorphosis into the postlarval form and settlement onto the sea bed, starting the adult, benthic, existence. The distribution of the adults is tightly controlled by the requirement for muddy substrata in which to construct burrows. That dependency on suitable areas for settlement, bring about the importance of the larval distribution in guaranteeing successful recruitment into the benthic habitat. In areas where muddy sediments occur in isolated patches, the viability of N. norvegicus populations is strongly reliant on retention of the larvae above the parental grounds. Understanding the mechanisms (physical and biological) assisting on larval retention may lead to better interpretation of recruitment patterns and can be a useful tool for stock assessement and management, resolutions. In the Irish Sea, the most significant mud area is a geographically isolated patch in the deepest region of the western basin. In this region, where tidal stirring is weak, thermal stratification of the water column occurs every year, during the spring-summer period. Due to the local topography and water column stratification a seasonal, density-driven gyre develops in the region. When the surface \.vaters heat up, a dome of cold, dense, water becomes trapped in the deepest trough and isolated from the surrounding mixed waters by horizontal bottom fronts which are then responsible for the development of the cyclonic gyre . The gyre is a stable, consistent circulation feature present each year du ting the surface beating season (spring-summer) which coincides with most of the Norway lobster larval season and may therefore constitute the mechanism promoting retention of the larvae above th e mud patch. In this study a comprehensive set of biological and hydro graphic obse1vations was gathered in order to investigate the possible role of the western Irish Sea gyre in the retention of N. norvegicus larvae and maintenance of the local population. Special attention was dedicated to simultaneous obse1vation of oceanographic and larval distribution (spatial and vertical) patterns. The observations from this study confinned the stable and coherent nature of tl1e western Irish Sea gyre and its retentive effect was clearly shown by the trajectories of Argos drifte rs. The distribution of N. norvegicus la.ivae closely matched the gyre circulation, particularly towards the end of May-June, when the gyre was fairly well developed, highlighting its influence on th e retention of the planktonic lobsters above the mud patch and adult habitat. However, the larval hatching season was noted to start in March-April, when stratification of the water column and associated gyre was only starting to develop. At this stage of the season considerable numbers of larvae drifted away from the muddy area, especially on the southwestern side. The gyre circulation was strongest in July-August, when the larval season of N. norvegicus was already over. Despite tl1e apparent mismatch between the peak of la.ival production, in May, and the period of maximum retention it appears that recruitment of lobsters into the adult habitat has remained stable. Spawning stock size estimated from larva.I abundances, for the 1995 season, did not differ significantly from equivalent calculations carried out for the 1982 and 1985 seasons. In addition, fishe1y statistics have shown steady, high, N. norvegicus landings fig ures for many years. Together, this infonnation suggests that the western Irish Sea N ephrops norvegicus population is sustained by stable, successful recrnitment and the gyre seems to be assisting in that process. The larvae which are lost from the population do not appear to be crucial for its survival. The analyses of la.ival, spatial and vertical, distribution presented in this study constitute effective background information to include in biological/oceanographic models aiming at simulating the dispersal of Nephrops norvegicus larvae in the western Irish Sea. Such experiments can contribute to a better understanding of the recruitment patterns of the species and assist on stock assessement studies.