Distribution and behaviour of Acetes sibogae Hansen (Decapoda, Crustacea) in an estuary in relation to tidal and diel environmental changes

Abstract

Quantitative samples of Acetes sibogae were collected at 2 h intervals for 48 h at three sites across the axis of a tidal estuary to examine their distribution within the water body over tidal and diel cycles, and to assess the role of behaviour in maintaining population distribution in estuarine/coastal waters in relation to selected environmental factors. Water temperature, salinity, tidal height and light intensity were concurrently measured. Distribution of the shrimp across the estuary was uniform and consistent between daylight or dark periods, and among flood or ebb tides. Changes of A.sibogae abundance were related to light and tidal cycles at each site with higher catches in dark periods and during flood tides. Acetes sibogae also exhibited both nocturnal and tidal vertical movements in the water body, with greater numbers being only found near-surface rather than near-bottom during flood tides and at night. No significant differences in the distribution of size groups were found between any sampled levels of any site. Acetes sibogae was highly aggregated in the water body. It is suggested that aggregating behaviour and tidal and nocturnal vertical movements act to facilitate population maintenance in estuarine/coastal waters.