Hilsa shad (Tenualosa ilisha) is one of the most economically and ecologically important anadromous fish species of the northern Bay of Bengal and associated estuarine and wetland systems. Increase in environmental fluctuations and habitat degradation has highly influenced the distribution of hilsa and its biomass composition in estuarine wetlands. The present study investigates limnological, pedological, hilsa biomass and biomass composition in estuarine wetlands of Haldi river tributaries of southern Bengal.  

The present investigation was conducted year-long across three wetland stations, Geonkhali, Sutahata, Nayachar where varying environmental conditions were present. Seasonal and spatial variations in limnological parameters including pH, temperature, DO, free CO2, nitrate, salinity, and phosphate. The pedological characters such as soil pH, available nitrogen, available phosphorus, sand, silt, and clay content were also assessed. Hilsa biomass was classified into different classes as per their weight and statistically evaluated using one-way ANOVA, Spearman’s rank correlation, and Principal Component Analysis (PCA).

The research revealed important variances in space of a number of environmental variables as well as hilsa resource biomass and distribution. Highest seasonal variability was exhibited by salinity. Phosphate concentration was displayed a strong positive relationship with hilsa biomass in Stations 1 and 2 (p < 0.01). Station 3 had the highest total biomasses of hilsa and also a larger proportion of bigger-sized individuals at low salinities. The second season peak in biomass was post-monsoon and monsoon seasonal. PCA revealed that water phosphate concentration and soil nitrogen were positively correlated and also that salinity and silt content were negatively related to total hilsa biomass. The first two principal components account for 42.78% of the total variance.

The results in the present study suggests that nutrient availabilities, particularly phosphorus and nitrogen positively regulate hilsa biomass and increase in salinity restricts hilsa distribution within estuarine wetlands. This study emphasizes the significance of limnological and pedological parameters in shaping the productivity of hilsa and gives baseline information for estuarine fisheries management and conservation planning in Sundarban – associated wetland.