The aim of this work is to study the factors that influence nominal fishing effort in the Bay of Seine fishing fleets. The nominal fishing effort of a fishing vessel is modeled gear by gear according to the data of a 1991 investigation on practical fishing methods.These analyses give results on the influence of vessel characteristics and fishing strategy on the fishing effort. The role of both vessel characteristics and crew size are highlighted. The influence of the use of multiple gears on monthly nominal fishing effort per gear is quantified. The differences between fixed and mobile gears are shown, especially the fact that the amount of gear used depends on fishing strategy for fixed gears and fishing time depends on vessel size for mobile gears.These results are then discussed with regard to managing fishing effort. We conclude that management measures must be different for fixed and mobile gears and must take into account adaptability of the fishermen. (C) 2001 International Council for the Exploration of the Sea.