Effects of El nino-related drought on freshwater and brackish-water fishesin suriname, South America

Droughts associated with the El Nino-Southern Oscillation (ENSO) affected f ishes of brackish-water lagoons, freshwater swamps and a rainforest creek i n Suriname, South America. The mean rainfall in the period August to Februa ry in 22 El Nino years was 76.6% of the mean rainfall in the same months of non-El Nino years. In the period 1900-1999, three out of four years in whi ch an extreme drought (rainfall less then 60% of the mean value) occurred w ere El Nino years. The recent 1997/1998 ENSO event caused the second most s evere drought in a 100-year record. Drying up of brackish-water lagoons, fr eshwater swamps and rainforest creeks was observed during El Nino-related d roughts. In the lagoons ariid catfish died first, followed by snook, tilapi a, mullet and tarpon, respectively. Landings of lagoon fish were positively correlated with rainfall in the period August-February. During the El Nino -related drought we observed failure of reproduction in three species of ca llichthyid armoured catfish in both coastal freshwater swamps and a rainfor est creek in the interior. In the El Nino year 1997/1998, the 'no flow' per iod of the rainforest creek was extended by four months beyond the long dry season and the dissolved oxygen levels in the dry-season pools dropped to 1.27 mg O(2)l(-1) (as compared to 4.53 mg O-2 l(-1) under running water con ditions). Other fish species of the rainforest creek also showed decreased reproductive success in the El Nino year. We suggest that the stochastic ef fects of El Nino-related drought may be an important non-equilibrium compon ent in the ecology of neotropical inland fish communities.