Assessing stocks of Mystus tengara (Hamilton, 1822) from three different management systems in Baors (Oxbow lake) of southwest Bangladesh: Implications for sustainable management.

This study was conducted to observe the stock assessments of Tengara (Mystus tengara) in three different management systems of Baors (Oxbow lake) such as System-1, System-2, and System-3. In this study, 1806 specimens were sampled using traditional fishing nets to observe growth pattern, population structure, growth parameters, natural mortality ( M ), fishing mortality ( F ), total mortality ( Z ), recruitment pattern, exploitation rate ( E ), relative yield per-recruit ( Y'/R ), optimum catchable length, length at first capture, steady state biomass ( SSB ), and maximum sustainable yield ( MSY ) from January to December 2021. Digital slide calipers and a digital balance were used to measure each individual's total length ( TL ) and body weight ( BW ), respectively. An empirical maximum length-based model was used to calculate size at first sexual maturity ( L m ), and optimum catchable length ( L opt ) was calculated based on asymptotic length ( L ∞ ). The least square linear regression equation was used to determine the regression parameters. The value of regression parameter, ' b ' was 3.01 for system-1, 2.78 for system-2, and 2.70 for system-3, indicating that growth pattern of Tengara is isometric in system-1, but negative allometric growth in system-2 and system-3. The highest asymptotic length ( L ∞ ) and weight ( W ∞ ) of Tengara were found in system-1 (11.19 cm and 13.67 g) in comparison with system-2, (10.98 cm and 12.49 g) and system-3 (9.09 cm and 6.96 g) respectively. The growth coefficient ( K ) of the von Bertalanffy growth function (VBGF) was 0.72 year-1 , 0.72 year-1 , and 0.73 year-1 for system-1, system-2 and system-3, respectively. The calculated M, F, Z were 1.72, 1.28, and 3.00 year-1 for system-1, 1.11, 0.67 and 1.78 year-1 for system-2 and 1.12, 0.84 and 1.96 year-1 for system-3 respectively. The calculated life span ( t max ) was found 4.19 years for system-1, 4.15 years for system-2 and 4.12 years for system-3. The recruitment patterns showed that the highest relative percentage of recruits were found in July, June and September for system-1, system-2 and system-3 respectively, with the major recruitment peak occurring from April to June for system-1, May to June for system-2 and June to July for system-3. One minor recruitment peak also occurred from August to September in system-1. The exploitation rate was more or less same in all three systems indicating that Tengara is under exploited from all the Baors . The significantly highest SSB and MSY were found in system-1 (22.65 and 12.11 metric tons), compared to system-2 (16.16 and 10.28 metric tons) and system-3 (5.55 and 5.49 metric tons), respectively. Considering the values of regression parameters, recruitment pattern, SSB and MSY , system-1 was found more suitable for Tengara compared to system-2 and system-3 management practices of Baors . Finally, these findings will turn out to be paradigm for the impregnable management of Tengara in Baors of southwest Bangladesh.