VARIABILITY IN NORTHWEST IRISH SEA NEPHROPS POPULATIONS

A high degree of spatial variation in Nephrops size, female maturity a nd sex ratio was observed. Disaggregated total catch size frequency da ta for male Nephrops from the western Irish Sea are described for the period 1968-1990. Temporal variation is discussed by reference to sub- areas of ICES rectangles in an attempt to look for long-term trends wi thin different parts of the Irish Sea. The data showed that if localis ed temporal change has occurred it is probably masked by spatial varia bility. Because of this spatial variability within rectangles the data are pooled from all rectangles in order to reduce the variance and so give an overall view of the western Irish Sea stocks. Despite this tr eatment no temporal trend in mean size was apparent. The stable sex ra tio observed in temporal data is tabled as evidence of stock stability , though it is emphasised that the situation should be carefully monit ored in view of the high fishing effort on Irish Sea Nephrops.