Analyse et estimation des puissances de peche

-An analysis of the fishing power concepts leads to a distinction between local fishing power (at a given location). and overall fishing power. Overall fishing power takes into account the ability to detect and quickly exploit rich areas. In order to estimate local fishing power it is necessary to compare the catches of different ships operating in neighbouring areas. Such a comparison performed on two ships will give an estimate of their relative fishing powers. The closer the two ships are, the more reliable will be the estimate. A weighting function must be used, and this function is related to the spatial heterogeneity of the fish density. Such a function is provided by the variogram as defined by Matheron (1965).- Overall fishing powers can be estimated using Robson's method (1966) where no division into spatial blocks is made: the fact that a ship is in a rich or a poor area must be related to the strategic component of its overall fishing power. A comparison between local and overall fishing powers may give a good insight of the strategic activity of the fishing fleet. The North East Atlantic albacore (Thunnus alalunga) surface fishery, more precisely its French component, has been studied as an example. The variograms have been estimated and appear to give a significant description of the spatial heterogeneity of the fish density. Individual local and overall fishing powers have been estimated. These calculations give information about the relative influences of local fishing powers and strategic abilities in overall fishing powers. If the strategic index is defined as the ratio of the overall to the local fishing power it appears that the local fishing power is generally the major component of the overall fishing power of a ship; and that the strategic component cannot be neglected as important differences occur between individual strategic indices. The first result may not be true within the Spanish fleet where some ships are unable to reach the best areas at the beginning of the fishing season. Some explanations emerge cbncerning individual local fishing powers and strategic indices. Local fishing power must be related first to type of gear used (bait boats and trollers appear in the fishery), and secondly to the home port of a ship. The strategic index must be essentially related to the home port. Some statistical inferences are possible only from the estimates of local fishing power. The differences which appear between yearly estimates of the strategic index of the same ships suggest that strong random components affect these estimates.