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Status and Distribution of the Gangetic Dolphin, Platanista Gangetica Gangetica (roxburgh, 1801) in River Buriganga During 2003-2004 and Its Conservation

Shayer Mahmood Ibney Alam
Department of Zoology, Jagannath University, Dhaka 1100, Bangladesh

Noor Jahan Sarker
Department of Zoology, University of Dhaka, 1000, Bangladesh

Abstract/ Executive Summary:

Studies on the population status, distribution and conservation issues of the Gangetic dolphin Platanista gangetica were undertaken in the river Buriganga from November 2003 to November 2004. A total of 29 sightings with the highest of five sightings and a best-high-low estimate of 9-11-7 individuals were recorded in November 2004, while in the months of August and October no dolphin was observed. The mean density was 0.25 dolphin/km and the highest encounter rate was 0.29 sightings/km. Of the total sightings, 41.38% were in the groups of more than one individuals. Of the observed dolphins, 71.43% were adults, 16.66% maturing and 11.9% young. The dolphins were found in 15 locations with both single as well as multiple sightings. Main threat to the dolphins was found to be pollution followed by traffic load and dredging activities.

Keywords: Platanista gangetica gangetica, Buriganga river, Status, Distribution, Conservation.

Location: The river of Buriganga, Bangladesh

Start Date: 00-11-2003

End Date: 00-11-2004

Program Area: Conservation and Biodiversity

Commodity: Aquatic animal

Objectives:

To assess the population size, distributional pattern and conservation concerns of the dolphins in the River Buriganga,

Methodology:

From the description of IWM, the Buriganga, having a length of only 17 km, is one of the most important rivers in Bangladesh. It flows through the southwest of Dhaka city and meets the river Turag near Mirpur and Dhaleswari at Hariharpara. The average width of the river around Dhaka city is nearly 500 m and the total area is estimated to be 3.4 km², i.e. 340 hectare. Generally, the flow of the Buriganga is non-tidal during wet season and tidal in dry season. However, the flow in the Buriganga becomes tidal in wet season when backwater effect is strong and upstream flow is small (IWM 2004). Buriganga is not an isolated river as Balu, Dhaleshwari, Kaliganga, Karnatali, Lakhya, Tongi khal and Turag River are hydraulically connected with Buriganga and influence its flow. During the last two decades, the river has turned up as the most polluted river in the country due to the release of tremendous amount of domestic and industrial pollutants (IWM 2004). The tannery industries in the Hazaribag area, Tongi, Fatulla and Tejgaon industrial areas directly or indirectly drains waste into Buriganga. Numerous industries on the bank not only directly discharge harmful wastes into the river, but also encroach it. This has changed the water quality to such a degree that sustainability of the aquatic ecosystem is questionable, especially in the dry season. Due to pollution, fish production in Buriganga has been reduced to an alarming level IWM. Both primary (direct observation) and secondary data (from journals, books and different organizations as IWM) were collected on the population status, distribution and conservation issues of the Ganges River Dolphin in the Buriganga. Observations were made by moving along the river using engine boats (trawler), at least once a month from November 2003 to November 2004 (13 months), except for the month of July 2004 due to flood. The whole length of the Buriganga used to be covered on the same day. People living near the river, specially the boatmen and the fishermen, were interviewed and asked for information about sightings of dolphins, propeller collision, past and present distribution, etc. They were shown pictures of the dolphins to avoid confusion. We tried to calculate the number of vehicles, both mechanized and non-mechanized, crossing through seven different points from 10.30 a.m. to 1.00 p.m. We also counted the number of standing vehicles at different points to figure out the traffic load at different times of the study period. A pre-constructed data sheet was used to record the required data. Secondary data on water levels and water quality in different months of Buriganga River were collected. Coordinates of different areas were obtained in WGS84 format using website http://itouchmap.com/latlong.html. Statistical analyses, such as mean, standard deviation and correlation were done using MS Excel.

Source of Information: Bangladesh J. Zool. 40(1): 21-31, 2012

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The study found that the most of the threats to the Gangtic dolphins (Platanista gangetica gangetica) in the river Buriganga were anthropogenic that shaped their status and distribution within the river. The Buriganga itself is a small river of only 17 km and there is a gap in the distribution of these dolphins that have concentrated them on the both ends of the river. The Government has taken steps to relocate the tannery industries. But there are other industries rather than tanneries that drain pollutants directly and indirectly into the river. Moreover, increasing number of industries has increased traffic loads in the river. Such rising threats will decrease their chances of existence. As the river plays a great role in communication with the capital Dhaka, declaration of any sanctuary for the dolphins in the river is virtually impossible. So, from the scientific point of view, it will be an opportunity to observe the condition whether the population bounces back or not after the removal of the tanneries.

Knowledge Management: Journal