Seasonal and diurnal changes in the fish fauna composition of a mangrove lake in the Caeté estuary, north Brazil

Abstract

Due to the construction of a road 20 years ago, the headwaters of an intertidal mangrove creek in the Rio Caeté estuary, near Bragança, Pará State (north Brazil) became a quasi-isolated lentic environment whose limnological characteristics are determined by precipitation and rare estuarine connections during high spring tides. We studied the fish fauna of this shallow artificial 0.19 km2 mangrove lake. Gill net sampling conducted during 24 hour cycles in three wet and three dry season months captured 639 fish of 19 species. Achirus achirus (Soleidae), Centropomus pectinatus, C. undecimalis (Centropomidae), and Mugil curema (Mugilidae) accounted for 82% of the total catch weight. Marine, estuarine and freshwater fish accounted for 71%, 27% and 2% of the total catch weight, respectively. CPUE was low (mean: 15.8 g m-2 24 h-4 or 0.1 individuals m-2 24 h-1) and did not differ between seasons, but catches were highest at sunset and lowest during daylight hours. In the dry season, several species disappeared from the catches, possibly as a result of the hypersaline conditions (>40 ‰) and very low water level in the lake. The origin (fresh, brackish or marine) and size of the fish caught suggest that most species became land-locked as juveniles during the wet season (i.e. freshwater conditions (0.7 ‰), high water level) and grew up in the lake. Spawning in the lake was recorded only for A. achirus. Our results suggest that re-connecting the lake to the tide channels would be beneficial for those fish populations as well as for local fisheries. Road construction through mangrove areas - if not avoidable at all - should preserve the natural watershed connections to minimize habitat degradation and maintain the proper dynamics of the tides in these environments. © MPI für Limnologie, AG Tropenökologie, Plön; INPA, Manaus.