Population Dynamics of Five Important Commercial Fish Species in the Sundarbans Ecosystem of Bangladesh: Recent Advancement | Chapter 3 | Current Research Trends in Biological Science Vol. 1

Aims: To determine the population dynamics and assess the exploitation level of Mystus gulio, Acanthopagrus latus, Chelon parsia, Otolithoides pama and Lates calcarifer in the Sundarbans ecosystem of Bangladesh. Study Design: Monthly length-frequency data of five fish species were collected from the Sundarbans ecosystem. The lengths of five fish species were recorded to the nearest one cm intervals in each month. Place and Duration of Study: The study was conducted from January to December 2011 in the Sundarbans ecosystem in Bangladesh. Methodology: The FAO-ICLARM Fish Stock Assessment Tools (FiSAT II) software was used to estimate the von Bertalanffy growth parameters (L and K), mortality coefficients (Z, M and F), probability of capture, recruitment pattern and Yield/Biomass-per-recruit for five commercially important fish species caught by fishers in the Sundarbans ecosystem of Bangladesh. Results: In the Sundarbans ecosystem of Bangladesh area the values of asymptotic length (L) for Mystus gulio, Acanthopagrus latus, Chelon parsia, Otolithoides pama and Lates calcarifer were found to be 23.0 cm, 33.6 cm, 30.0 cm, 32.5 cm and 55.0 cm respectively while the growth co-efficient (K) were 0.75, 0.85, 1.1, 0.8 and 0.5 respectively. The estimates for L (23.00 – 55.0 cm) and K (0.5-1.1 year-1) obtained were consistent with those available in the literature. Relatively high K and low L values, typical of short-lived tropical fishes, were obtained for Mystus gulio, Acanthopagrus latus, Chelon parsia and Otolithoides pama. The length growth performance index (’) of the Pauly and Munro’s function was in the range of 2.599 – 3.180. Natural mortality, fishing mortality and total mortality were in the range of 0.956-1.89, 0.55-1.58 and 1.52-3.3 respectively. Estimates for total mortality (Z) and natural mortality (M) imply low annual rates of survival and high turnover rates. The recruitment pattern suggested one main pulse of annual recruitment. The exploitation rate was estimated to be between 27% and 47% and the length at first capture was estimated to be approximately 19-54% of L. The exploitation rate obtained for five fish species are relatively lower compared to other available studies in the coastal areas of Bangladesh. The growth and exploitation rates obtained were compared with available estimates to evaluate the consistency of the results with current knowledge about the species in the region. Conclusion: The study indicated that the length-at-first-capture/L seem to be a simple parameter, which could be used to make a rapid assessment of the status of the stocks. All together, the present study reveals that the population of these five studied species attains acceptable sustainability levels in the Sundarbans ecosystem and scope for a slight increase in catch efforts. 

Author(s) Details  

Md. Golam Mustafa
Center for Resource Development Studies Ltd, 13C/8C Babar Road, Block B, Mohammadpur, Dhaka 1207, Bangladesh.

Imran Ahmed
Department of Forest, Bon Bhaban, Agargaon, Dhaka 1207, Bangladesh.

Mohammod Ilyas
WorldFish, South Asia, Level 5-7, House 2/B, Road 4, Block B, Banani, Dhaka 1213, Bangladesh.

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The Population Dynamics of the Mudskipper, Periophthalmus barbarus (LINNEAUS 1766) (TELEOSTEI, GOBIIDAE) and the Implication for Conservation and Management in the Mangrove Swamp of Iko River Estuary, Southeastern Nigeria | Chapter 05 | Recent Advances in Biological Research Vol. 3

The population dynamics of Periophthalmus barbarus in the mangrove swamp of Iko River estuary, southeast of Nigeria were obtained from a twenty four month length composition data ranging 4.6 – 14.5 cm total length (TL) (mean 9.1841± 1.6346: n = 2,876) corresponding to 1.16 – 50.6 g total weight (TW) (mean = 9.9626 ± 5.4796) the growth was exponential. The asymptotic length (L∞) of the Powell-Wetheral plot (L∞ = 15.03 cm) was seeded into FSAT II (FAO-ICLARM Stock Assessment Tools II) software to obtain best estimates of von Bertalanfy growth parameters as L∞ = 16.22 cm TL, growth coefficient (K) = 1.2 year-1, age of fish at zero length, to = 0.071, longevity, tmax = 2.5 years. The estimated growth performance index, φ’ = 2.449. Other FISAT II growth parameters were the amplitude of growth oscillation, C = 0.6 and the winter point, WP = 0.6, Rn = 0.3127. Mortality parameters were total mortality, Z = 479 year-1, natural mortality, M = 2.39 year-1 and fishing mortality, F was 2.40 year-1. Result indicate the fishery is optimally exploited with current exploitation rate, Ecur = 0.50 < Emax = 0.668 > Eopt = 0.5 which suggests stock optimal exploitation, corroborated by Z/K ration (3.184).  Ecur (0.5) means that 50% of the available stock is being fished annually. The length-at-first capture Lc = 7.33 cm TL and Lc/L∞ was 0.45, indicating the fish was yet to complete 55% of growth as at the time of capture at Lc, hence P. barbarus in the ecosystem is at the optimal level of exploitation as well as the presence of growth overexploitation. Thus to circumvent the consequences of growth overfishing, sustainable fisheries measures such as monitoring of fishing effort, use of selective gears and increase in mesh size should be encouraged, implemented and enforced. The study has revealed that P. barbarus population residing in the mangrove swamp of Iko River Estuary is experiencing exploitation rate close to the maximum sustainable yield amidst the presence of heavy fishing pressure. Moreover, the mudskipper fishery in this ecosystem is currently exhibiting growth overexploitation signs which could lead to severe implications on the population size and food security within vulnerable fishing households in the future. Therefore, urgent management interventions in the form of monitoring fishing efforts, return of captured juveniles back to the water body from the non-selective fishing gear and use of selective gear with large mesh size (to increase length at first capture) are needed to safeguard this important fish species from possible collapse in the future.

Author  Details:

Dr. Nsikak Abiaobo

Department of Zoology, Akwa Ibom State University, Ikot Akpaden, Mkpat Enin, P.M.B. 1167, Akwa Ibom State, Nigeria.

Dr. Mfom Tmothy Udo

Department of Fisheries and Aquatic Environment Management, University of Uyo, P.M.B. 1017, Akwa Ibom State, Nigeria.

Read full article: http://bp.bookpi.org/index.php/bpi/catalog/view/50/397/427-1

View Volume: https://doi.org/10.9734/bpi/rabr/v3