Assessment of offshore shrimp stocks of Bangladesh based on commercial shrimp trawl logbook data

Abstract

This study presents the results of analytical assessment of offshore shrimp stock in Bangladesh marine waters. A time series of annual catch per unit effort (CPUE) was derived from commercial logbook data during the period from 1986 to 2016 and used as a turning series for a Schaefer biomass model. The current stock size and annual harvest rate were estimated to be around 20300 t and 20% respectively, with the stock size increasing in the last ten years. The estimated maximum sustainable yield (MSY) reference points with 95% confidence intervals are optimal biomass B MSY = 15800 t (11300-22000 t) and optimal harvest rate u MSY = 30% (21-42%). The average annual catch was 4650 t, close to the estimated MSY of 4710 t (4570-4860 t). Overall, the stock is estimated to be in a good state and the data show that CPUE in recent years is slightly above the long-term average. The assessment results are subject to considerable uncertainty, reflected in wide confidence intervals around the estimated stock status. Moreover, the simple assessment model has restrictive assumptions that may not capture the underlying dynamics of the Bangladesh shrimp fishery, a multispecies tropical fishery with changes in the fleet composition and fishing technology. Nevertheless, the model fits well to the CPUE data and the assessment is a valuable basis for giving short-term and long-term management advice.

Stock Assessment and Rebuilding of Two Major Shrimp Fisheries (Penaeus monodon and Metapenaeus monoceros) from the Industrial Fishing Zone of Bangladesh

“…However, these indices can be misleading in a multi-gear and multi-species fishery (i.e., marine fisheries of Bangladesh) if a proper standardization technique for the catch and effort data is not employed [36]. Studies that assessed shrimp populations using catch and effort data from the marine water of Bangladesh reported the over-exploitation and depleted stock biomass [23,[37][38][39][40][41][42][43]. Unfortunately, these studies used the effort data presented in the "Yearbook of Fisheries Statistics of Bangladesh" [17] without any evidence of standardization, which could be affected the estimation of fisheries reference points.…”

Stock assessment using Bayesian state-space surplus production models: the case of bonga shad, Ethmalosa fimbriata (Bowdich, 1825), in the Eastern Central Atlantic Ocean

“…Additionally, the stock's performance under various MSY inflection points for the Schaefer (1954), Fox (1970), and Pella and Tomlinson (1969) surplus production functions will for the first time be assessed and management implications drawn from the optimal model. Besides, a multi-model approach to fish stock assessment has been shown to provide a wider understanding of stock status (Barua et al 2023; Konoyima et al 2023). Furthermore, this study will conduct robust convergence diagnostics of the input data and assess the sensitivity of reference points to retrospective changes in the assessment time series to improve confidence in stock status estimates for the evaluated species.…”

Application of Length-Based Assessment Methods to Elucidate Biological Reference Points of Black Pomfret Stock in the Bay of Bengal, Bangladesh

“…Alongside, shrimp trawlers largely catch shrimps as target species with various finfish species. Shrimp trawlers usually have 150-250 mt gross tonnage capacity and a power of 500-900 HP, which allows for 30 days in a trip [32][33][34]. The smaller wooden trawlers were approved to sail for 14 days, and steel hull trawlers for 30 days in a trip [30,31].…”

“…For the estimation of fishing mortality, a linearized length-converted catch curve (LCCC) was produced from the length data and growth parameters. Then the instantaneous mortality rate (Z) was calculated from the slope of the regression line of the descending part of the catch curve [32]. The natural mortality (M) was then calculated using the following formula proposed by Then et al (2015) [46]:…”