Stock assessment of barred spiny eel, Macrognathus pancalus (Hamilton, 1822) in a wetland ecosystem, northwestern Bangladesh: A fundamental approach to ensure sustainability and conservation

This research delved into the management approach for Macrognathus pancalus within the Gajner Beel of northwestern Bangladesh, employing a comprehensive array of length-based indicators. The study encompassed an investigation into population structure, growth parameters (including asymptotic length (L_∞), asymptotic weight (W_∞), growth coefficient (K), and age at zero length (t₀)), mortality parameters, growth performance indices, recruitment pattern, exploitation rate (E), relative yield per-recruit (Y'/R), optimum catchable length (L_opt), longevity, biomass, and maximum sustainable yield (MSY). The TL and BW ranged from 5.00 to 16.20 cm and 0.49 g–17.20 g for males, and 7.80–18.80 cm and 1.25–29.75 g for females. The overall b value of LWR indicated positive allometric growth for both males and females. The size at first sexual maturity (L_m) was measured 9.74 cm for males and 11.16 cm for females in TL, while calculated age at first sexual maturity (t_m) (year) was 0.83 for males and 0.84 for females. The L_∞ and W_∞ values were determined as 17.15 cm, 23.20 g for males and 19.86 cm, 41.40 g for females. Growth performance indices for males and females were found to be 2.26 and 2.60, respectively. The longevity of males and females was estimated at 4.84 and 4.76 years, respectively. L_opt values were recorded as 9.65 for males and 11.14 cm for females. Calculated M values were 0.95 year⁻¹ for males and 0.97 year⁻¹ for females, while F was determined as 1.29 year⁻¹ and 1.51 year⁻¹ for males and females, respectively. Total mortality (Z) was found to be 2.24 year⁻¹ and 2.48 year⁻¹ for male and female M. pancalus populations. The E were calculated at 58% and 61%, while the MSY indicated 46% and 49%, underscoring the need for a 12% reduction in fishing pressure for both males and females to prevent overexploitation. The findings offer valuable insights for the sustainable management of M. pancalus in the Gajner Beel and its surrounding habitats, underlining the urgency of conservation efforts.