Variability of, and the influence of environmental factors on, the recruitment of postlarval and juvenile Penaeus merguiensis in the Matang mangroves of Malaysia

Postlarval and small juvenile Penaeus merguiensis were sampled fortnightly by beam trawls on the ebb tides over 4 years in the Matang mangroves on the west coast of peninsular Malaysia. Larger juveniles were sampled by bag nets on both the ebb and flood tides every fortnight over 5 years. Rainfall is consistently high throughout the year (> 100 mm in each month) and the annual rainfall ranges from about 1,800 to 2,600 rum. Water temperatures ranged from 27degreesC to 36degreesC and salinity from 14parts per thousand to 32parts per thousand during this study. Fortnightly catches by beam trawls and bag nets were highly variable but showed a single broad period of postlarval and juvenile recruitment extending from December to May and an extended broad period of juvenile emigration from February to July. Beam trawl catches of postlarvae and juvenile prawns were consistently low between June and August. Higher catches of postlarvae and juveniles were recorded at two sites in close proximity to small adjoining creeks than one with no adjacent creek. Catches of juveniles in bag nets were higher during the day than the night and were correlated with the strength of the water flow. Environmental variables generally accounted for only a small proportion of the variation in catches, even for rainfall. The small proportion of variation explained by environmental variables is probably because of their relatively small seasonal variation in the Matang region. The lack of environmental influence on the catches of P. merguiensis implies that managing the mangrove nursery habitats and fishing pressure may be the main considerations for sustaining their stocks in the Matang region.