Length-based stock assessment and population dynamics of two flat fishes, in relation to environmental parameters from Hooghly estuary (Bay of Bengal), India: implication for sustainable resource management.

The present research focused on a detailed stock assessment of Cynoglossus cynoglossus and Brachirus orientalis in the Hooghly estuary from January to December 2023. Length-weight data from 1601 specimens of C. cynoglossus and 550 of B. orientalis were analysed using FISAT-II. The analysis revealed that both species exhibited positive allometric growth. The growth parameters L, K, and ϕ were 162.7 mm, 0.54 year, and 4.17 for C. cynoglossus and 152.2 mm, 0.36 year, and 3.97 for B. orientalis respectively. Estimated (t) lifespans were 3.15 years for C. cynoglossus and 6.72 years for B. orientalis. Total, natural, and fishing mortality rates (Z, M, F) were 2.29 year, 0.89 year, and 0.97 year for C. cynoglossus and 1.71 year, 0.54 year, and 1.17 year for B. orientalis. In both species, fishing mortality (F) exceeded natural mortality (M) with exploitation rates (E) of 0.57 for C. cynoglossus and 0.42 for B. orientalis, surpassing their corresponding E values of 0.44 and 0.40 respectively. The commercial catch length groups fell below the size at first maturity, 105.7 mm for C. cynoglossus and 114.5 mm for B. orientalis, indicating premature harvesting before spawning. The environmental parameters, such as water pH, temperature, DO, salinity, hardness, and alkalinity, remained within the suitable range for fish growth. However, the current exploitation rates suggest that overfishing poses a significant threat to the wild stock of both species. The findings of this study are crucial for developing appropriate fishing regulation and management strategies to ensure the sustainable use of aquatic resources, not only in the Hooghly estuary but also in other tropical estuarine ecosystems worldwide.