The swimming behaviour and distribution of Neomysis integer in relation to tidal flow

The behaviour and distribution of the estuarine mysid shrimp, Neomysis integer, were investigated in relation to a variety of flow regimes in the field and in the laboratory. In the field, Neomysis aggregated in low-flow areas, such as in the lee of rocks and macroalgal clumps. Over the low-tide period and during ascending and high-tide periods, individuals were concentrated in a band toward the moving tide edge where flows are typically low. Experiments performed using a laboratory flume demonstrated a clear response of Neomysis to flow, the proportion of individuals above the bed declining with increasing flow. At flows of up to 10 cm s(-1), 90-95% of individuals were able to maintain position on the bed of the flume, but at flows greater than this, Neomysis were unable to maintain position. When provided with a choice of water depths in a laboratory static tank (zero flow), there was little evidence of depth-seeking behaviour. We suggest that avoidance of areas of high how is a key factor determining the local distribution of Neomysis. (C) 1999 Elsevier Science B.V. All rights reserved.