Population biology of the Norway lobster, Nephrops norvegicus (L.) in the Firth of Clyde, Scotland I: Growth and density

The density, size composition and growth of Nephrops norvegicus were examined at six sites in part of the Firth of Clyde, SW Scotland, between 1990 and 1992. Sampling was carried out using small mesh trawls and by an underwater television camera. The growth of male Nephrops at each site was investigated by analysis of length–frequency distributions using the computer program ‘‘Multifan’’. Estimates of Nephrops density at each station were obtained from TV counts of burrows and from relative trawl catch rates. Both density measures were correlated and showed a similar pattern between stations, although burrow counts exceeded trawl catches by roughly two orders of magnitude. Marked geographical variations were recorded in both the growth (L£ and K) and density parameters, and L£ was found to be inversely correlated with burrow density, suggesting that growth may be density-dependent. The weighted annual mean carapace length of Nephrops in trawl samples was significantly correlated with L£, suggesting that mean size data may provide a useful indicator of growth variability within and between populations. On the other hand, the maximum carapace length (Lmax) of Nephrops in samples was found to provide an unreliable estimate of L£. The results are discussed in relation to possible environmental influences on growth and population density.