A METODOLOGY TO ESTIMATE CATCH BY FISHING AREA FROM LITTLE INFORMATIVE DATA SET: THE OF SKIPJACK TUNA (Katsuwonus pelamiS) FISHERY IN BRAZILIAN COAST

Abstract

The cosmopolitan species, skipjack tuna (Katsuwonus pelamis), is an important pelagic fishery in southern Brazilian coast. Skipjack is available to surface pole and line gear in a wide area all the year round. Catches are carried out from south of Bahia (19°S) to Rio Grande do Sul (34°S). However, there are wide seasonal and geographic variations of the fishing effort suggesting shifts of school concentrations along the coast during the year. Despite this established knowledge, the skipjack catch or relative abundance by month and fishing area cannot be directly estimated because available information of the governmental fishery reports pools data from the entire Brazilian coast. Estimates of such relative abundance indices by area are critical to understand the population dynamics and life cycle of the skipjack tuna in the Southwest South Atlantic. In order to calculate these indices and to detect small scale variations of the skipjack tuna weight catch, the entire southern Brazilian coast was divided in three fishing areas. The Catch per Unit of Effort (CPUE) assumed as an index of relative abundance, was defined as catch by fishing day. Since there are great differences between vessels, before CPUE calculation, the fishing effort was standardized through fishing power estimates. The CPUE value in each area and month was assumed as representative of the relative area contribution to the total monthly catch. The results point to wide differences between individual participation of fishing areas to the total monthly catch. These individual contribution by fishing area, showed great variations along the year. The oceanic area of the south coast is very important to skipjack tuna fishery around the summer, while in the winter, the fleet shifts northwards and the oceanic area on the brazilian southeast coast becomes the main fishery area