Oceanographic characteristics of a multi-specific fishing ground of the Central South Brazil Bight

In the Central South Brazil Eight, a multispecific demersal trawl fishery i s conducted by trawlers licensed for the industrial pink shrimp (Penaeus pa ulensis and Penaeus brasiliensis) fishery. In addition to the pink shrimp, many by-catch species have become increasingly valued in the last two decad es. In spite of the importance of this multispecific fishery, the oceanogra phic characteristics of the inner continental shelf, onshore the 100 m isob ath, are poorly known. In this paper we present, for the fist time, monthly oceanographic records taken from December 1995 to May 1997 with the R/V 'D iadorim' at two of the main fishing grounds of this region. Water temperatu re data showed the formation of a strong thermocline during summer, from No vember to April. This thermal gradient, due to the South Atlantic central w ater (SACW) intrusion that reaches these shallow waters, disappeared with t he homogenization of the water column during autumn and winter, from May to September. This cold and low salinity water does not originate from local river discharges, but also represents an advection of sub-Antartic water ma ss. After this and during spring, a new thermocline develops, reaching its maximal expression from February to March. A maximal gradient was registere d in February 1997, when the temperature dropped from 26 degrees C at 7 m t o 16 degrees C at 14 m depth. This result shows that the SACW intrusion is a large-scale phenomenon that regularly influences the whole inner continen tal shelf up to 20m. Demersal fishing grounds located in this area were cov ered during summer by a cold and nutrient-rich mass of water that resulted in an unusual maximum of chlorophyll a values near the bottom (30 m). The h omogenization of the water column and the presence of another cold water ma ss during winter resulted in a strong semi-annual thermal cycle on the bott om. The role of this important oceanographic process in fishery production and dynamics deserves further investigation, but the data presented here sh ow evidence for the importance of this phenomenon.