In this paper data on catch and effort by gear are analysed, for weakfish (Macrodon ancylodon) landed at Santos from January 1959 to December 1963. The region studied was a narrow band about 30 nautical miles wide, along the southern coast of Brazil, between 23º S and 34º S. From the analysis of monthly data of production per unit-effort by squares of 1º on a side, we divided the studied region in two areas: area I (from 23º S to 27º S) and area II (from 28º S to 34º S). The index of unit-effort production and the effort concentration index were computed grouping the data by quarters. From the results we may drow the following conclusions: 1 - In a general way, the effort for catch weak-fish has been applied satisfactorily because the medium and large parejas have operated almost in areas with average density on¹ higher than average density; 2 - The production per unit-effort in the area I is smaller than the production in area II, which suggests that the index of abundance is higher in area II; 3 - The decrease in production per unit-effort, in area II, suggests a decrease in the abundance or availability of weak-fish in this area; 4 - In the area I, the index of production per unit-effort remained approximately at the same level.