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Hydrographic Status of Sundarbans Mangrove, Bangladesh with Special Reference to Post-larvae and Juveniles Fish and Shrimp Abundance

M. Enamul Hoq
Bangladesh Agricultural University, Faculty of Fisheries, Mymensingh 2202, Bangladesh

M. Abdul Wahab
Bangladesh Agricultural University, Faculty of Fisheries, Mymensingh 2202, Bangladesh

Abstract/ Executive Summary:

Environmental factors, including water parameters, were correlated with assemblages of mollusca and finish post-larvae and juveniles in the 5 rivers of Sundarbans mangrove for 2 years, located in the south-west of Bangladesh. Fifteen species of mollusca fish belonging to 6 families and 37 species of finfish belonging to 27 families were recorded. Four species of shrimp (Metapenaeus monoceros,M. brevicornis, Macrobrachium Villasimius and Acetesspp.) and megalopa of crabs (79.3–96.83%), and 4 species of finfish (Panchaxmelastigma, Liza parsia, L. tade and Gobidae) (40–76%) were the most abundant species. Significant(p<0.05) inter-month variations in temperature, transparency and chlorophyll-a; inter-month and inter-river variations in salinity, conductivity and TDS were observed in the Sundarbans water. Ordination on correlation coefficients between temperature and salinity with the abundance of dominant species showed that Acetes spp. and Gobidae were abundant in high salinity and high-temperature areas; Stole-phorus triin low salinity and high-temperature areas; Macrobrachiun villosimanus, Leiognathusspp. and Liza tade in low salinity and low-temperature areas, however, other species showed variations among 2 years of study. Out of 7 dominant mollusca fishes, 4 species showed positive correlation to temperature, pH and TDS; 3 species to salinity, transparency, conductivity and chlorophyll-ain the river water. Among 8dominant fish species, 4 species were found to positively correlate with temperature and pH; 3 with salinity, conductivity and chlorophyll-a; 6 with transparency and 5 species showed a positive correlation to TDS in Sundarbans water. Abundance of Penaeus monodon also showed a positive correlation to observed water parameters except for chlorophyll-a.

Keywords: Hydrology, Post-larvae, Mollusca and finfish, Sundarbans mangrove

Location:

Start Date:

End Date:

Program Area: Conservation and Biodiversity

Commodity: Plant, Fish

Objectives:

The present paper aims to examine the abundance and distribution of PL and juvenile communities in relation to various water parameters. The results have been discussed in terms of the correlation between the measured parameters and the distribution of species in the Sundarbans mangrove.

Methodology:

Study area: The Sundarbans, declared as ‘‘world Heritage Site’’ by UNESCO in 1999, is located between longitudes 89°00¢E and 89°55'E and latitudes 21°30'N and 22°30'N. The Sundarbans is a deltaic swamp. The land surface is essentially flat and variations exit are micro topographical only. Generally, the highest land is immediately adjacent to the water-courses, where sediment is deposited when tide overflows their banks. Based on salinity ecological zonation, intensive sampling of post-larval shrimp and fish was carried out in five river systems of the Sundarbans, located about 40–50 km upstream from the Bay of Bengal estuary. Passur, Sibsa and Koyra rivers represent freshwater, Kholpatua river represents semi-saline and Madar river form saline zone. The forest vegetation of the studied areas is comprised of sundri (Heritiera fomes, Sterculiaceae) in the Passur river area; sundri, passur (Xylocarpusmekungensis, Meliaceae) and kankra (Bruguieragymnorhiza, Rhizophoraceae) with scattered baen (Avicennia officinalis) in the Sibsa and Koyra river area; gewa (Excoecaria agallocha, Euphorbiaceae), goran (Ceriops decandra, Rhizophoraceae) with fewsundri in Kholpatua and Madar river area. These rivers had been sampled monthly for 2 years from June 1998 to May 2000. ost-larval sampling A rectangular dragnet with a length of 2 m including cod-end and a mesh size of 2 mm, was used for sampling. The net at the opening made of bamboo spilled structure (1.6·0.6 m2) and a plastic bucket was attached at the cod end for collecting sample materials, which is slightly modified from those widely used for wild P. monodon PL collection in coastal waters. A synthetic monofilament net material (high-density polyethylene) with knot-less webbing was used to make the sampling net. The net is comparable with sampling nets used in coastal waters of India (Mohan et al. 1995; Rajendran and Kathiresan 1999). Water parameters Water samples for the determination of physico-chemical parameters were collected during the collection of mollusca and finfish samples from the surface of each sampling sites by a clean bucket. Water transparency was measured with a standard Secchi disc of 20 cm diameter. The temperature of surface water, salinity, conductivity and total dissolved solids (TDS) were measured directly with a direct reading integrated conductivity meter (Jenway 4200 Conductivity Meter). the pH of the water was measured using a portable pH meter (pH Scan-2, sensitivity 0.1±0.02), which was calibrated with pH buffer, 4.0 and 7.0 before every use.

Source of Information: Wetlands Ecology and Management (2006) 14: 79–93

Article Link (Online Journal): DOI 10.1007/s11273-005-2569-

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Out of 7 dominant mollusca fishes, 4 species showed a positive correlation to temperature, pH and TDS; 3 species to salinity, transparency, conductivity and chlorophyll-ain the river water. Among 8dominant fish species, 4 species were found to positively correlate with temperature and pH; 3 with salinity, conductivity and chlorophyll-a; 6 with transparency and 5 species showed a positive correlation to TDS in Sundarbans water. The abundance of Penaeus monodon also showed a positive correlation to observed water parameters except chlorophyll-a.

Knowledge Management: Journal