Use of intertidal and adjacent mudflats by juvenile penaeid shrimps during 24-h tidal cycles

Abstract

Trawl tows every 3 h throughout 24-h tidal cycles at 0.6, 1.0 and 2.0 m depths along three transects sampled the extensive intertidal and immediate subtidal mudflats in north Kuwait Bay on 4–5 June and 25–26 June, 1989. Results showed catch rates of Penaeus semisulcatus De Haan, 1844, Metapenaeus affinis (H. Milne Edwards, 1837), Parapenaeopsis stylifera (H. Milne Edwards, 1837), and M. stebbingi Nobili, 1904 to differ significantly with the main effects of diel period, depth, and tide. Interactions differed depending on species. All species were 2–5 times more catchable at night than during day. The shrimp species could be partitioned into two categories: subtidal mudflat specialists included P. semisulcatus, P. stylifera and M. stebbingi, and intertidal mudflat specialists as represented by M. affinis. Common to all subtidal mudflat specialists were increased catch rates with depth and increased catches at low tide. Highest catches of subtidal mudflat specialists usually included combinations of night, 2 m depths, and low tide. In contrast, M. affinis catch rates increased significantly with decreasing depth. Results show that the subtidal mudflat specialists remain in the area of low–low tide throughout the tidal cycle, while the intertidal mudflat specialist, M. affinis, followed the tidal front as it advanced and retreated across the intertidal area. Apparent catchability varied widely depending on timing and location showing the importance of establishing sampling criteria prior to conducting a sampling programme for recruitment indices. The behaviour patterns demonstrated by the species examined here are believed to result from predator avoidance with subtidal mudflat specialists using low tide and the cover of darkness for protection, while M. affinis utilized the shallow intertidal waters on mudflats where shrimp predators were few.