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Population Dynamics of Jatka (juvenile Hilsa) in the Meghna River, Bangladesh

S. M. Nurul Amin
Bangladesh Fisheries Research Institute Riverine Station, Chandpur-3602 Bangladesh

M.A. Rahman
Bangladesh Fisheries Research Institute Riverine Station, Chandpur-3602 Bangladesh

G.C. Haldar
Bangladesh Fisheries Research Institute, Riverine Station, Chandpur-3602 Bangladesh

S. Nahar
Bangladesh Fisheries Research Institute, Riverine Station, Chandpur-3602 Bangladesh

S. Dewan
Department of Fisheries Management, Bangladesh Agricultural University Mymensingh Bangladesh

M.A. Mazid
Bangladesh Fisheries Research Institute, Mymensingh Bangladesh

Abstract/ Executive Summary:

Population parameters of the jatka (juvenile hilsa, Tenuolosa ilisha) were estimated using FISAT software with length-frequency data collected from the Meghna River (Shatnol to Hajimara), Bangladesh. The predicted extreme length was 19.34 cm (95% probability of occurrence). Based on the von Bertalanffy growth equation, the ultimate (asymptotic) length of the jatka was estimated as 18.60 cm while the predicted best growth coefficient (K) was 8.80/year. The annual rate of natural mortality (M) and fishing mortality (F) were found to be 8.39 and 14.13, respectively. The estimated value for the exploitation rate (E) was 0.63. The length-weight relationship of jatka was found to be W = 0.00736 TL³⁰⁹². The present investigation indicated overfishing (E > 0.50) of jatka in the Meghna River.

Keywords: Jatka, Meghna river, Mortality

Location: Meghna River (Shatnol to Hajimara), Bangladesh.

Start Date:

End Date:

Program Area: Resource Development and Management

Commodity: Hilsa

Objectives:

To estimate the natural mortality (M), fishing mortality (F) and exploitation rate (E) of jatka.

Methodology:

Every month (January to April 1999) the length-frequency data of the jatka were collected from different places in the Meghna River (Satnol to Hajimara). Total length (TL) of 2,296 jatka in the size range 2 to 18 cm were measured using a meter scale (± 1 mm) while the weight of 375 jatka were taken using an electronic balance of 0.0001 g accuracy. The data were then analyzed. Total mortality (Z) was estimated using the length converted catch curve method. Natural mortality rate (M) was estimated using Pauly's empirical relationship i.e. Log₁₀ M = - 0.0066 - 0.279 Log₁₀ L_∞ + 0.6543 Log₁₀ K + 0.4634 Log₁₀ T where L_∞ is expressed in cm and T, the mean annual water temperature in °C which here is 27°C. Fishing mortality (F) was obtained by subtracting M from Z and exploitation rate (E) was obtained from F/Z [E = F/Z = F/ (F+M)]. An estimated length structured VPA of jatka was carried out by employing the growth and mortality parameters. The to value was taken as zero.

Source of Information: Asian Fisheries Science 13(2000): 383-389; Asian Fisheries Society, Manila, Philippines

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The results of length-structured virtual population analysis (VPA) indicated two peaks of fishing mortality (F). The highest peak of F occurred in the length range between 3.5 to 5.5 cm with the value of F exceeding 8 which may be associated to excessive use of large seine net locally known as jagat ber jal (mesh size 0.5 to 1.5 cm). Another peak occurs in the length range between 10.5 to 15.5 cm which could be attributed to the current jal (mesh size 1 to 2.5 cm).

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