VARIABILITY IN NORTHWEST IRISH SEA NEPHROPS POPULATIONS

A high degree of spatial variation in Nephrops size, female maturity and sex ratio was observed. Disaggregated total catch size frequency data 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 within different parts of the Irish Sea. The data showed that if localised temporal change has occurred it is probably masked by spatial variability. 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 treatment no temporal trend in mean size was apparent. The stable sex ratio observed in temporal data is tabled as evidence of stock stability, though it is emphasised that the situation should be carefully monitored in view of the high fishing effort on Irish Sea Nephrops.