POPULATION-DYNAMICS OF THE KRILL MEGANYCTIPHANES-NORVEGICA (SARS,M, 1857) (CRUSTACEA, EUPHAUSIACEA) IN THE LIGURIAN SEA (NW MEDITERRANEAN-SEA) - SIZE STRUCTURE, GROWTH AND MORTALITY MODELING

The seasonal abundance, population structure and dynamics of the eupha usiid Meganyctiphanes norvegica were studied from samples taken year r ound in the NW Mediterranean Sea Length-frequency distributions were g enerally bimodal: the first mode was interpreted as the born-in-the-ye ar cohort (0+) and the second as a combination of the older age classe s (1+). To describe growth, a bilinear function provides the best fit. A growth rate of 0.052 mm day(-1) (1.56 mm month(-1)) was calculated for the first part of the growth function and 0.0034 mm day(-1) for th e second part. A negative exponential mortality function was fitted, g iving a mortality rate of 0.0034 day(-1) (1.25 year(-1)). A numerical simulation of the size structure of the Ligurian population was perfor med and the validity of the model was checked using a multifactorial a nalysis. The demographic characteristics of the Ligurian population we re compared to those of other areas and were interpreted as a function al adaptation of M.norvegica to the southern part of the geographical distribution of the species.