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Population Parameters of Important Species in Inland Fisheries of Bangladesh

M. G. MUSTAFA*
The WorldFish Center, Bangladesh and South Asia Office House No. 22B, Road No. 7 Block F, Banani, Dhaka 1213, Bangladesh

G. DE GRAAF
Nefisco foundation, Lijnbaansgracht 14C 1015 GN Amsterdam, the Netherlands

Abstract/ Executive Summary:

The von Bertalanffy growth model parameters (L∞ and K) and mortality coefficients (Z, M and F) were estimated for 12 fish species caught by fishers in five Community-Based Fisheries Management project sites in Bangladesh. The exploitation ratio (E=F/Z) and gear selectivity (L50) were also estimated for each species. The growth and exploitation parameters obtained were compared with available estimates to evaluate the consistency of the results with current knowledge about the species in the region. The estimates for L∞ (7.0 – 24.0 cm) and K (1.077±0.328 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 nine species. Estimates for Z (1.86 – 6.55) and M (1.22 - 3.06) imply low annual rates of survival and high turnover rates. The estimates for M obtained were consistent with those available in the literature for the 12 species. The exploitation rate was estimated to be between 34 and 53% and the length at first capture was estimated to be approximately 32-56% of L∞. The study indicated that the length-at-first-capture/L∞seems to be a simple parameter that could be used to make a rapid assessment of the status of the stocks.

Keywords: Population parameters, Important Species, Inland fisheries, Bangladesh

Location: Bangladesh

Start Date: 00-10-2002

End Date: 00-09-2003

Program Area: Socio-economic and Policy

Commodity: Fishery policies

Objectives:

The present study was undertaken to estimate population dynamics parameters and the extent of exploitation to support decision-making in the Community Based Fisheries Management project implemented by the WorldFish Center.

Methodology:

The study was conducted in five perennial water bodies within the Community Based Fisheries Management (CBFM) project (de Graaf & Mustafa 2003) which is working in the inland waters of Bangladesh to manage fisheries resources in 117 water bodies involving up to 23,000 poor fisher families. The key characteristics of the water bodies and major species diversity. The study was conducted from October 2002 to September 2003. Monthly length-frequency data were collected from the Ashura beel, Dik-shi beel, Mara beel, Shapla beel and Medi beel. The lengths of major fish species in the catch of individual fishers were recorded to the nearest 0.5 cm during a 20 day period in each month. For each sample the gear type and mesh size were recorded. All length-frequency data for each month were pooled across species, gear types, mesh size and study areas. Simultaneous catch data were collected for a duration of four to eight days per month per site every month. The daily catch of every individual fisher was considered as the catch per unit of effort (CPUE), the numbers and weights of the dominant fish species in the catch were recorded. Furthermore, the gear-type and its mesh size were recorded. Length-frequency data analysis For the estimation of the growth rates, only samples from non-selective gears, such as lift net, scoop net and seines were used and aggregated in monthly periods. Population parameters were estimated using the FAO-FISAT software (Gayanilo et al.1997). In Bangladesh, fish growth exhibits a distinct seasonal pattern with high growth during the monsoon and low growth during winter (Halls et al. 1998; de Graaf et al. 2001; de Graaf 2003). Correlation among different parameters Correlation among the estimated values for area (ha), relative fishing effort (no. fisher x ha^-1x year^-1), catch per unit of area (kg x ha^-1x year^-1), catch per unit of effort (kg x fisher^-1x day^-1), exploitation rate (%), growth (cm), longevity (year) and Lc50/L∞ in the different sites were determined with SPSS with a significance level of 0.05.

Source of Information: Asian Fisheries Science 21(2008):147-158

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The study indicated that it was not easy to compare the multi-species multi-gear fisheries with the standard fish stock assessment method so the best option would be to convince all stakeholders that we reached the limit and that no new gears can enter the fishery. However, the correlation among the different parameters estimated at the five sampled sites indicates that Lc50/L∞ is significantly related to the exploitation rate and the ratio of Lc50/L∞ could be used to monitor the health of fish stock by the fisher’s communities.

Knowledge Management: Journal