The nursery function of sandy beaches in a Brazilian tropical bay for 0-group anchovies (Teleostei: Engraulidae): diel, seasonal and spatial patterns

Abstract

The role of sandy beaches as nursery areas for 0-group anchovies (Teleostei: Engraulidae) was investigated in a tropical bay, south-eastern Brazil. Spatial and temporal (diel and seasonal) changes in fish abundance and environmental influences at two beaches were assessed, one located in the outer zone, and the other in the inner zone of Sepetiba Bay. The two sites were sampled quarterly at the same time (0800, 1100, 1400, 1700, 2000, 2300, 0200 and 0500 hours) over a 24 h cycle by beach seine with three replicates, between winter 1998 and autumn 1999. Environmental variables of water temperature, salinity, and transparency (as % depth) were taken at each fish-sampling occasion. Five species in three genera (Anchoa tricolor, A. januaria, A. lyolepis, Cetengraulis edentulus, and Lycengraulis grossidens) were identified. Anchoa tricolor and A. januaria were the most abundant species and indications of spatial separation were detected, with A. tricolor being more abundant in the outer bay (higher salinity and lower temperature), while A. januaria, in the inner bay (lower salinity and higher temperature). Overall, young-of-the-year Engraulidae peaked during the day, perhaps an adaptation to avoid competition with other abundant species which peak at night. Maximum densities of anchovies due to 0-group influxes were found in spring and paucity in summer. Spatial segregation to optimize resource uses and daily habits adapted to take advantage of the rich planktonic bay waters seems to be the strategy developed by these closely related species to use the area during early life cycle. Their high abundances suggest the suitability of the sandy beaches as nursery areas.