Marion Verdoit

Most demersal and benthic fish populations exhibit spatial and seasonal patterns in relation to their annual life cycle. Many fishes migrate from spawning area toward feeding area at some periods of the year. Despite the importance of these spatial and seasonal features, most presently used management models omit this resources structuration, the population is supposed to be randomly distributed over all its distribution area and during all the year. Furthermore, these models are based on the assumption of maximal legal catches and effort over the whole area of distribution during all the year, and fishing exploitation is represented by a constant mortality during all the year and the studied area. It seems that a way to reduce overexploitation could be to propose finer management measures aiming at distributing fishing effort on seasons and spatial patches (for instance by a closure of area at a given season). Such management measures require both a good knowledge of the biological cycles of the populations and structured models in space and time.

The objectives of this thesis are double. The first aim is to describe and analyse the heterogeneity of the spatial and temporal distributions of two of the main exploited resources from the Celtic Sea, Norway lobster and whiting. This description is based on analysis of scientific survey data and on commercial catch and effort data, but also on the previous knowledge on the main features of annual life cycle of exploited populations.

The second objective is to define mathematical models of the dynamics of each of the studied population, structured in space and time, from results coming from the first step. Mathematical models could allow to validate some hypotheses about biological cycles, to identify some unknown parameters, and to test assumptions related to the maintenance of the populations at a stable levels. So, the thesis is composed of a statistical data analysis phase and a modelling phase.

Keys words : spatial and seasonal distributions, CPUE, commercial catch and effort data, scientific data, whiting, Nephrops norvegicus, Celtic Sea, factorial analyses , multivariates analyses , contiguity analyses, discrets models , spatial modelling, population dynamics.

Verdoit M., and Pelletier D., 2000. Characterizing the spatial and seasonal dynamics of the whiting population in the Celtic Sea from the analysis of commercial catch and effort data and scientific survey data. ICES 2000 Annual Science Conference. 27-30 September 2000. Bruges, Belgium.

Verdoit M., 2000. Analysis of spatial and temporal distribution of the Norway lobster population from the Celtic Sea and choice of the pertinent features to model its dynamic. Seminar study and control of ecological models. Zoological station of Villefranche- sur-mer. 3 march 2000.

Verdoit M., 1999. Modelling the spatial and seasonal distribution of exploited demersal and benthic populations in the Celtic Sea. Colloque Fragmentation and delays in population dynamics. CIRM Luminy, 29 march- 2 april 1999.