DISTRIBUTION AND ABUNDANCE OF MEGRIM (LEPIDORHOMBUS-BOSCII AND LEPIDORHOMBUS-WHIFFIAGONIS) ON THE NORTHERN SPANISH SHELF

The distribution and abundance patterns of the two species of megrim. LL Lepidorhombus whiffiagonis and L.. boscii, in ICES Divisions VIIIc and IXa, were analysed using the data provided by bottom-trawl surveys and the Spanish fishing fleet in European Atlantic waters. The consis tency of year-class strengths estimated over time from these surveys w as taken as an indication of the reliability of the survey data to mon itor megrim population abundance. Recruitment strength was, to a large extent, the main factor governing abundance found in successive years . This is due to the fact that the greater percentage of accessible bi omass comprises 1. 2 and 3-year-old individuals. Four spot megrim (L. boscii) is currently the most abundant species in this zone due to the weak recruitment of L.. ir pp in recent years. As a consequence of th ese species' sexual differences in growth. there is a predominance of females in the larger-sized individuals of the population. From 4 year s onwards, males show a higher mortality rate than females. No evidenc e of geographical migrations was found, although a bathymetric expansi on occurs with age: juveniles are more stenobathic than adults are. A degree of specialization can be observed in the two species' habitats, probably due to their different feeding systems, with L. whiffiagonis occupying shallower waters. Production statistics from the Spanish fi shing fleet in the north-east Atlantic show a far wider distribution o f L. boscii than was indicated by data available previously. (C) 1998 International Council for the Exploration of the Sea.