Population dynamics and stock assessment of Red snapper (Lutjanus johnii) in the Bay of Bengal Bangladesh waters

Red snapper (Lutjanus johnii) is one of the most significant commercial fish species in the marine waters of Bangladesh. A comprehensive understanding of the biology and dynamics of fish is important for the effective management of the fishery. Therefore, it would be the first study on this highly valuable commercial species to draw stock status and assessment of reference points in the upper Bay of Bengal, Bangladesh using three different length-based methodological approaches which are TropFishR (Tropical Fisheries Analysis with R), LBSPR (Length-based Spawning Potential Ratio), LBI (Length based Indicators), and a catch-based method DB-SRA (Depletion-based Stock Reduction Analysis). An allometric growth pattern (b=2.66) was observed in the length-weight relationship of Red snapper. The VBGF (von Bertanlanffy Growth Function) life history parameters for Red snapper were L∞=99.33 cm, k=0.16 year−1, and based on LCCC (Length Converted Catch Curve) analysis, the total mortality (Z=0.59 year−1), natural mortality (M=0.24 year−1) and fishing mortality (F=0.35 year−1) were estimated. The results show that this fishery is currently likely to be overfished due to overexploitation and the stock’s spawning biomass (SPR=28%) is below the target reference point because most of the catch (72%) was found to have under the maturity level. This study recommended a length to catch between 51 and 62 cm and proposed a yearly landing limit of 175 mt as OFL (Over Fishing Limit) for the next ten years in line with the annual fishing ban to raise the stock’s biomass over the Bmsy level for maintaining sustainable yield of 271 mt as MSY.