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Population Dynamics of Notopterus Notopterus (pallas, 1769) from the Kaptai Reservoir of Bangladesh

M. Golam Mustafa
Noakhali Science and Technology University (NSTU), Sonapur-3814, Noakhali, Bangladesh

S. Singha
Noakhali Science and Technology University (NSTU), Sonapur-3814, Noakhali, Bangladesh

M. R. Islam
Noakhali Science and Technology University (NSTU), Sonapur-3814, Noakhali, Bangladesh

Nayan Mallick
Institute of Marine Science and Fisheries, University of Chittagong, Chittagong-4331, Bangladesh

Abstract/ Executive Summary:

Population parameters of Notopterus notopterus from length-frequency data collected from Kaptai Reservoir of Rangamati, Bangladesh from January, 2013 to December, 2013 were calculated by using FiSAT software. The asymptotic total length (L_∞) and growth coefficient (K) were estimated to be 34.91cm and 0.38 y⁻¹ respectively. The instantaneous rate of natural mortality (M), fishing mortality (F) and total mortality (Z) were estimated to be as 0.91 y⁻¹, 0.28 y⁻¹ and 1.19 y⁻¹respectively. The value of exploitation rate (E) was found to be 0.24 which clearly pointed toward moderate or less fishing pressure (E<0.50) of N. notopterus in the Kaptai reservoir of Bangladesh. The recruitment of the species was found throughout the year with two peaks - one from March-April; and another from May- June. Virtual population analysis (VPA) estimated that the maximum numbers of N. notopterus were caught between 10.50 cm to 32.50 cm with maximum F value (0.80 y⁻¹) in the mid length of 18.30 cm. During the year 2013 the total catch of N. notopterus was found to be 664.5 MT, which contributed about 7.78% of the total catch of Kaptai Lake. Relative yield per recruit (Y’/R) and biomass per recruit (B’/R) suggested that the natural mortality should be reduced to 0.91 y⁻¹ by proper management to obtain a maximum sustainable exploitation rate (E_max = 0.828) for the species in the reservoir.

Keywords: Asymptotic length, Growth coefficient, Mortality, Virtual Population Analysis, Recruitment pattern, Exploitation rate, Notopterus notopterus

Location: Kaptai reservoir of Rangamati and Chittagong

Start Date: 00-01-2013

End Date: 00-12-2013

Program Area: Socio-economic and Policy

Commodity: Fish

Objectives:

To determine the population parameters of N. notopterus using length-frequency based analysis collected from Kaptai reservoir of Rangamati, Chittagong, Bangladesh.

Methodology:

Experimental fish of this research work was Notopterus notopterus. The study area of this research work was Kaptai reservoir (22°29′45″N and 92°13′45″E) of Rangamati, Chittagong, Bangladesh which is the largest man-made freshwater body in Bangladesh with a total surface area of 68,800 hectare and average water depth is about 9 meters with maximum depth of 32 meters. The selected sampling stations for this research work were fish landing centre of Bangladesh Fisheries Development Corporation (BFDC) and local markets (Natun Bazar, Jetty Ghat Bazar) near Kaptai reservoir. Total 555 raw fish samples were collected for one year from January 2013 to December 2013. Samplings were done monthly at a regular interval directly from the BFDC fish landing centre and local fish markets (Natun Bazar, Jetty Ghat Bazar) of Rangamati district. These fish samples were collected by the fishermen from Kaptai Lake using gill net and lift net. In case of gill netting, the fishermen used a wide range of mesh sizes (6-14 cm). Total Asymptotic Length (L_∞) and Growth Coefficient (K)was estimated. This led to a preliminary estimate of L_∞ and K that were used to obtain “probabilities of capture” by length class using the routine in FiSAT. These “probabilities of capture” were used to correct the length frequency distribution data to account for incomplete selection and recruitment and the final estimates of L_∞ and K were obtained by using these corrected length distribution data through ELEFAN I. ELEFAN I was used to estimate the growth parameters based on the Von Bertalanffy Growth Formula (VBGF). Mortality Estimation, Probability of Capture, Recruitment Pattern, Virtual Population Analysis (VPA) and Relative Yield-per-Recruit and Biomass-per-Recruit eas estimated using standard methods.

Source of Information: SAARC J. Agri., 12(2): 112-122 (2014)

Article Link (Online Journal): http://www.banglajol.info/index.php/SJA/article/view/21923/15038

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Kaptai reservoir is considered safe from human activities and it is capable of supporting various fish species including N. notopterus. From the findings of the present study it can be concluded that the stock of N. notopterus is more or less under optimum exploitation 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.

Knowledge Management: Journal