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Population Dynamics of Bombay Duck Harpodon Nehereus (hamilton, 1822) of the Bay of Bengal Along Bangladesh Coast

M.N. Sarker
Bangladesh Marine Fisheries Capacity Building Project, Department of Fisheries, Matshya Bhaban, 13, Shahid Captain Monsur Ali Sarani, Ramna, Dhaka-1000, Bangladesh

Md. Humayun
Center for Development Initiatives in Capture Fisheries (CDICF), 27/A, Siddeshwari Lane, Ramna, Dhaka-1217, Bangladesh

Md. Atiar Rahman
Bangladesh Marine Fisheries Capacity Building Project, Department of Fisheries, Matshya Bhaban, 13, Shahid Captain Monsur Ali Sarani, Ramna, Dhaka-1000, Bangladesh

Md. Sharif Uddin
Bangladesh Marine Fisheries Capacity Building Project, Department of Fisheries, Matshya Bhaban, 13, Shahid Captain Monsur Ali Sarani, Ramna, Dhaka-1000, Bangladesh

Abstract/ Executive Summary:

Population parameters of Harpadon nehereus were estimated using FiSAT-II. length-frequency data collected from different landing centers along the coast of Bangladesh. The Von Bertalanffy growth parameters L and K for the species were 45.05 cm and 1.30/year, respectively. The annual rate of natural mortality (M) and fishing mortality (F) were found to be 1.86 and 2.58, respectively. The estimated value of the exploitation rate (E) using the length converted catch curve was 0.58 and E max was found to be 0.582. The recruitment pattern of this species was continuous and two peaks per year. The present investigation clearly showed the over fishing (E > 0.50) condition for H. nehereus in Bangladesh. The estimated length-weight relationship for the combined sex was found to be W = 0.003199 L3.

Keywords: Asymptotic length, Growth coefficient, Mortality, Virtual population analysis, Exploitation rate, Harpadon nehereus.

Location: The study area was from Cox’s Bazar to Satkhira. Data collected from 35 selected marine fish landing stations under 49 upazilla of 14 districts along the coastal belt of the Bay of Bengal.

Start Date: 00-09-2013

End Date: 00-08-2014

Program Area: Animal Health and Management

Commodity: Aquatic animal

Objectives:

The present study was undertaken to estimate the key parameters of stock assessment and its population dynamics like asymptotic length (L∞), growth coefficient (K), total mortality (Z), natural mortality (M), fishing mortality (F), exploitation rate (E), recruitment pattern, relative yield/recruit (Y/R), relative biomass/recruit (B/R) and virtual population analysis (VPA) etc. for H. nehereus.

Methodology:

Length-frequency data of Harpadon nehereus were collected weekly from the commercial catches from 35 different landing centers of Bangladesh coastal districts from September, 2013 to August, 2014. Samples of H. nehereus were mainly caught by set bag net, seine net and gill nets. Random samples of 6,411 specimens were collected. The length-frequency data were pooled month-wise. Study area: The study area was from Cox’s Bazar to Satkhira. Data collected from 35 selected marine fish landing stations under 49 upazilla of 14 districts along the coastal belt of the Bay of Bengal. Data processing and analysis: Estimation of Asymptotic length (L∞) and Growth co-efficient (K): Month-wise length-frequency data were used to estimate the total asymptotic length (L∞ cm) and growth co-efficient (K/year) of the Von Bertalanffy growth equation (Bertalanffy 1938, Beverton and Holt, 1957). The data collection period started from September and continued up to August 2013. The ELEFAN I and ELEFAN II routines incorporated in FiSAT II (FAO ICLARM Stock Assessment Tools) Software (Gayanilo et al. 2005) were used to determine L∞ and K values following the Powell-Wetherall method (Wetherall et al. 1987). This method was used to provide an initial estimate of L∞. This initial estimate of L∞ was then used as seed value to determine the value of K (Silvestre and Graces 2004). Minor adjustments to L∞ and K were made to maximize the ‘goodness of fit’ criterion built in to ELEFAN I (Pauly 1987). This led to a preliminary estimate of L∞ and K that were used to obtain “probability of capture” by length class using the routine in FiSAT. These “probability of capture” were used to correct the length-frequency distribution data to account for incomplete selection and recruitment and the final estimate of L∞ and K were obtained by using the corrected length-frequency data through ELEFAN I (Silvestre and Graces, 2004). ELEFAN I was used to estimate the growth parameters based on the Von Bertalanffy Growth Formula (VBGF) expressed in the form (Pauly and Gaschutz 1979): Mortality estimation: In FiSAT II software package (Gayanilo et al, 2005, ELEFAN II was used to estimate the total mortality Z (per year) using the length converted catch curve by means of final estimates L ∞ and K and lengthfrequency data (Beverton and Holt 1957, 1966) for the species H. nehereus. The rate of natural mortality M (per year) for the species was calculated by using Pauly’s empirical equation (Pauly 1983): Recruitment pattern: Recruitment Pattern was obtained by the backward projection of the frequencies on the time axis of a time series of samples along a trajectory defined by the Von Bertalanffy growth equation (Moreau and Cuende 1991). This routine reconstructs the recruitment pulses from time series of length-frequency data to determine the number of pulses per year and the relative strength of each pulse (Gayanilo et al. 2005). The values of Emax, E0.1 and E0.5 were estimated by using the first derivative of this function, where, Emax = Maximum sustainable exploitation rate, E0.1= Exploitation rate at which the marginal increase of relative yield/recruit is 1/10th and E0.5 = Value of E under which the stock has been reduced to 50% of its unexploited biomass.

Source of Information: Bangladesh J. Zool. 45(2): 101-110, 2017 ISSN: 0304-9027 (print) 2408-8455 (online)

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The Bay of Bengal is being considered with vast biodiversity and it is capable of supporting various fish species including H. nehereus. From the findings of the present study it can be concluded that the stock of H. nehereus is in overexploitation level. Any major change in the existing fishing level/exploitation will most likely result in a reduction in the yield per recruit and thereby hamper the MSY. Therefore, protection from any over exploitation, prohibition of indiscriminate fishing with non-allowable mesh size gears/nets, banning of fishing particularly during the spawning season of the studied species are recommended, which in turn will help to manage this fishery in a more sustainable way. The findings of the present study will help to formulate the management and conservation policies of this species and would be helpful for further development of this species in Bangladesh.

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