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Impact of River Salinity on Fish Diversity in the South-west Coastal Region of Bangladesh

A.K Gain*
Environmental Science Discipline, Khulna University, Khulna, Bangladesh

M.N.Uddin
Environmental Science Discipline, Khulna University, Khulna, Bangladesh

P.Sana
Environmental Science Discipline, Khulna University, Khulna, Bangladesh

Abstract/ Executive Summary:

Saline water intrusion is a major problem and conflicting issue in south-west coastal region of Bangladesh. The present study provides an assessment of changes of fish diversity with the changes of salinity level in the nearby river over the last thirty years. This study is carried out through semi-structured questionnaire survey in selected villages of different salinity prone areas such as high saline zone and moderate saline zone, namely Paikgacha and Rampal, respectively. The increased salinity has negative impact on fish diversity in this region. Local people’s perception,experts’ judgment was used in detecting decreasing of fish diversity with increasing in river salinity. The study has revealed that in Paikgacha, the salinity varies approximately within the range from 20,000 to 45,000 micromhos and in Rampal it is from 10,000 to 30,000 micro-mhos. Due to increased salinity, the fish species in Paikgacha and Rampal have been reduced from 29 to 12 and 24 to 19 species respectively during the period 1975-2005. Dominancy of very few salinity tolerant species is increasing in both areas but it is more visible in Paikgacha than Rampal.

Keywords: Fishermen, Perception, Trend analysis, Expert choice, Paikgacha, Rampal

Location: Paikgacha and Rampal

Start Date:

End Date:

Program Area: Conservation and Biodiversity

Commodity: Fish

Objectives:

This study was focused on the changes offish diversity due to change of river water salinity based on the perception of local fishermen.

Methodology:

The study area was selected randomly considering the factor that the area should have high or moderate saline zone. Considering the fact, Paikgacha under Khulna district (highly saline zone) and Rampal under Bagerhat district (moderately saline zone) was selected. Two unions were selected from the two sub-districts and from each union two villages were selected because two salinity measuring stations of Bangladesh Water Development Board (BWDB) for Shibsa river of Paikgacha and Passur river of Rampal are very close to the study area. Salinity data of these rivers represents the salinity state of the selected regions. Yearly maximum salinity level series of 27 years (1975 – 2004; 3 yr missing) of these two rivers was collected from hydrology department of BWDB. The statistical trend analysis was carried whether the time series data of salinity has the statistically significant positive trend or not in both two regions. The procedure of testing linear trends is described herein: t Assume that y, t = 1,..., N is an annual time series and N is sample size. Simple linear trend can be written as Where, D and M are the parameters of the regression model. Rejection of hypothesis M = 0 can be considered as a detection of a linear trend. The hypothesis that M = 0 is rejected if in which R is the cross-correlation coefficient between1Nthe sequences y, ..., y and 1, ..., N and is the quantile of the student t distribution with v = N – 2degrees of freedom. Then, trend line was drawn by using MS Excel which represented he changed level of salinity graphically from the year 1975 to 2004. To collect the fish diversity and related data, a semi-structured questionnaire through purposive sampling was prepared for the study. The sample size was determined following the principle of Berensen and Levine (1992) and this was 35 and 45 for Paikgacha and Rampal respectively. Household was selected as the sampling unit considering the factors that one member of each household.

Source of Information: International Journal of Ecology and Environmental Sciences 34 (1): 49-54, 2008

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The study findings show that fish diversity of the study area is reducing with the increase of salinity. The reduced fish diversity eventually decreases the fish production of native species and creates extinction of several species. These consequences eventually create instability in the socio-economic sector of the study area in terms of increased poverty of local fishermen. So, salinity is now a major problem in south west coastal region of Bangladesh. The Government should take immediate steps for reducing salinity level of the study area. The reduction of salinity level in south west region of Bangladesh can be accomplished by increasing freshwater flow from the Ganges through the Gorai-Madhumati channel.

Knowledge Management: Journal