Abstract
The Sundarbans forms an ideal mangrove ecosystem, supports large group of fish, shrimp, edible crab and also supply food and cash to local coastal communities. The composition, density and distribution pattern of shell- and finfish larvae and juvenile in the 5 rivers of upper Sundarbans with different salinity zones were investigated during June 1998 to May 2000, along with various environmental factors, present status of fishery and its nature of utilization.The structure and temporal distribution of the post-larvae and juvenile shell- and finfish community were studied, taking monthly or fortnightly day time samples with a rectangular drag net (2 mm mesh). Water quality parameters viz. transparency, pH, temperature, salinity, conductivity, TDS and chlorophyll-a were determined. Water and soil analysis (pH, organic matter and nutrients like N, P, K, Ca, Mg, Na and Fe) were also carried out in adjacent shrimp farms for comparison of productivity.Fifteen species belonging to 6 families of shellfish and 37 species belonging to 27 families of finfish were recorded during 2 years study. Four species of shrimp (Metapenaeus monoceros, M. brevicornis, Macrobrachium villosimanus and Acetes spp.) and megalopa of crabs were the most abundant (79.3-96.83%). Also 4 species of finfish (Panchax melastigma, Liza parsia, L. tade and Gobidae) were the most abundant fish species (40-76%). Among 15 commercially important species recorded, M. monoceros, L. parsia, L. tade and megalopa of Scylla serrata were predominant.Megalopa of crabs were most numerous, making up to 25.6% of the total shellfish catch, followed by M. villosimanus (21.19%), Acetes spp. (16.72%) and M. monoceros (14.38%). Liza spp. was the most numerous in total catch of finfish juvenile constituting 29.32%, followed by small fish P. melastigma (20.13%) and Gobidae (12.98%). The commercial species M. monoceros, Croakers and Liza spp. were observed frequently throughout the study period in addition to crab megalopa with maximum abundance occurring seasonally from November to February. No significant seasonal or lunar variation in abundance of shell- or finfish species was observed, although major annual peak in winter for shrimp and fish species and in monsoon for crab megalopa were recorded. Abundance of P. monodon PL significantly (P<0.05) varied with month and between 5 rivers. 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., Gobidae and P. koelreuteri were abundant in high salinity and high temperature areas; S. tri in low salinity and high temperature areas; M. villosimanus, Leiognathus spp. and L. tade in low salinity and low temperature areas, however, other species showed variations among 2 years sampling. On the other hand, no significant differences in water and soil profiles between Sundarbans mangrove and adjacent shrimp farms were observed, although seasonal variations in water quality were found. In both habitats, available soil nitrogen varied from 0.11 to 0.22%, indicating nutrient limitation. The reported yield of cultured P. monodon was 98 to 190 kg/ha during 150 to 180 culture days.The dried, salted and smoked fish and shrimp products of Sundarbans Reserve Forest (SRF) have been reviewed in terms of production process, marketing channel, and also product quality. The proximate composition and nutrient elements were determined in 20 dried fish and 2 shrimp species from Sundarbans coast. Dried fish/shrimp had protein contents between 59.26 and 74.1% but there was considerable variation in the fat content ranging from 5.55 to 19.98%, which are relatively rich sources of the macro-nutrient element such as calcium. The overall quality of the dried product is comparable to exported fish products of the country. Salted Tenualosa ilisha was nutritionally acceptable. The physical properties, proximate composition, nutrient content and amino acid values showed that the quality of smoked shrimp was quite good and retained its overall acceptability up to 60 days of storage.In depth analysis of statistical records from SRF showed that catch of major fishes like white fish and marketable shrimp has been reduced over the years, whereas catch of S. serrata is in increasing trend. At least 14 types of fishing gears are used in Sundarbans, majority of which has a relatively highly non-selectivity. Present study indicated that any set of fisheries management practice is almost non-existent in SRF resulting in serious over-exploitation of all the fish stocks and warrant immediate attention.