CAUSES AND SPATIAL SCALES OF VARIABILITY IN POPULATION-STRUCTURE OF NEPHROPS-NORVEGICUS (L) IN THE IRISH SEA

Male and female length frequency distributions (LFDs) of Nephrops norv egicus (L.) were spatially autocorrelated at different scales on a gri d of stations sampled in the Irish Sea in both 1989 and 1990. Female L FDs were correlated up to a range of 15 km and males up to 25 km. Clus ter analysis of the LFDs, interpreted taking into account the autocorr elation length scales, indicated two to three main clusters of geograp hically connected stations for male LFDs and smaller clusters with wea ker spatial contiguity of stations in the case of female LFDs. Inter c luster differences in median length, mean weight, range in length, siz e at putative ages 2 and 3 and the proportion of mature females were a pparent. These parameters reliably classified over 80% of stations to their respective clusters in a direct discriminant analysis. The biolo gical characteristics were partially dependent on sediment grain size composition as shown by a canonical correlation analysis. Median lengt h, mean weight, size at ages 2 and 3 and the percentage of females tha t were mature were all negatively correlated with finer sediments. The re was a stronger interdependence between the sediments and the female data, compared with the male data. Other factors which may be respons ible for the observed structures, such as fishing effort and bottom te mperature regimes, are discussed.