Effects of El Niño-related Drought on Freshwater and Brackish-water Fishes in Suriname, South America

Abstract

Droughts associated with the El Nino-Southern Oscillation (ENSO) affected fishes of brackish-water lagoons, freshwater swamps and a rainforest creek in Suriname, South America. The mean rainfall in the period August to February 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 which an extreme drought (rainfall less then 60% of the mean value) occurred were El Nino years. The recent 1997/1998 ENSO event caused the second most severe drought in a 100-year record. Drying up of brackish-water lagoons, freshwater swamps and rainforest creeks was observed during El Nino-related droughts. In the lagoons ariid catfish died first, followed by snook, tilapia, 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 callichthyid armoured catfish in both coastal freshwater swamps and a rainforest creek in the interior. In the El Nino year 1997/1998, the ‘no flow’ period 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 O2l−1 (as compared to 4.53 mg O2 l−1 under running water conditions). Other fish species of the rainforest creek also showed decreased reproductive success in the El Nino year. We suggest that the stochastic effects of El Nino-related drought may be an important non-equilibrium component in the ecology of neotropical inland fish communities.