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Present Status of Ganges River Dolphins Platanista Gangetica Gangetica (roxburgh, 1801) in the Turag River, Dhaka, Bangladesh

Mohammad Abdul Baki
Department of Zoology, Jagannath University, Dhaka 1100, Bangladesh

Naser Ahmed Bhouiyan
Department of Zoology, Jagannath University, Dhaka 1100, Bangladesh

Md. Saiful Islam
Department of Zoology, Jagannath University, Dhaka 1100, Bangladesh

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

Shibananda Shil
University Grants Commission of Bangladesh, Dhaka 1207, Bangladesh

Md. Muzammel Hossain
Department of Zoology, Jagannath University, Dhaka 1100, Bangladesh

Abstract/ Executive Summary:

Freshwater ecosystem degradation in the Turag River basin is increasing due to rising human settlement, reduced water flow during the dry season, new large land development projects, and toxic emissions caused by brick kilns. The population of river dolphins was estimated through surveys carried out from December 2012 to November 2013. Surveys were conducted on a fortnightly basis. The dolphins were counted within an 18.4 km stretch (known to be the most polluted stretch) of the 75 km long river. A total of 62 dolphin sightings were recorded, both as individual sightings and as groups. The highest monthly count was in August. The best high-low estimates of 9-11-7 individuals were recorded in August 2013 in river ecology. Seasonal changes in spatial distribution were observed. The survey revealed that rising floodwater stimulated an increase in the dolphin population in the study area from July to October. The maximum encounter rate was also 0.49 sightings km−1 for the month of August. The sightings and encounter rates of dolphins were lower from December to July (dry and premonsoon period) likely due to reduced water flow and adverse water quality of this river.

Keywords: Ganges River Dolphins, Platanista gangetica gangetica, Turag River, Dhaka, Bangladesh

Location: Turag River, Dhaka, Bangladesh

Start Date: 00-12-2012

End Date: 00-11-2013

Program Area: Conservation and Biodiversity

Commodity: Dolphin

Objectives:

This paper discusses the status (sightings of individuals and groups, dolphin density, encounter rates, and ecology) and distribution of the Ganges river dolphins in the most polluted section of Turag River and identifies areas where research and conservation activities are most needed. We emphasize collection of quantitative data for assessing the abundance of this river dolphin.

Methodology:

Study Period and Area. River dolphin survey was held in the Turag River from December 2012 to November 2013. The Turag River is about 75 km long, which was not feasible to cover in a day by the kind of motorboat used for survey. Therefore, the stretch of Amin Bazar bridge to Kamarpara bridge (approx. 18.4 km) was surveyed by motorboat for river dolphin study. The survey team always started observations from Amin Bazar bridge and surveyed all the way to Kamarpara bridge in the Turag River. The Turag River is an upper tributary of Buriganga, a major river in Bangladesh. The river is so polluted that it has been declared as an “Ecologically Critical Area (ECA)” by the department of Environment, Government of Bangladesh. This section of the river is situated around Dhaka city and lots of industries are situated by this section of the river. 2.2. Data Collection and Analysis. This study was conducted on a fortnightly basis. Boat-based surveys were conducted twice per month, giving a total of 24 surveys during the study. Boats maintained a constant speed range of 7–10 km/h. Survey design followed previous studies conducted by different authors. The observation team mostly consisted of three researchers. An average of 18.4 km of the river was covered in each survey. River average width is about 0.1 km. Sampling was undertaken in sighting condition in the river. The locations of dolphin sightings were recorded by a Garmin Map 72 GPS. We considered a single platform with 2 primary observers and 1 rear observer. Surveys began at 07:00 h and ended at 16:00 h during clear weather conditions in the river. Two primary members were positioned at the front of the boat and left and right of a data recorder and continually searched for dolphins using binoculars and occasionally with unaided eyes. Eye height was 1.5 m above the water surface. During survey period one interviewer visited river bank (other platform) and conducted a cross-check interview with boatmen and fishermen about sightings of dolphin. The question was “Did you see the susu or dolphin” Once a dolphin or a group was sighted, the number of individuals was recorded with a best-high-low estimate of group size. Encounter rates (sightings km−1), for each survey, were calculated by dividing the sightings (events) by the total distance surveyed. The direct count method was used to estimate the population. 2.3. Hydrology of the River. The Bangladesh Water Development Board (BWDB) set up a water level monitoring station at Turag River to forecast the flood gauges in Dhaka city. This station was located for daily monitoring of Turag River’s water level, which included staff gages. Therefore, this study collected daily water depth data during the study period from the BWDB office (72 Green Road, Farmgate, Dhaka, Bangladesh).

Source of Information: International Journal of Zoology Volume 2017, Article ID 8964821, 7 pages

Article Link (Online Journal): https://doi.org/10.1155/2017/8964821

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The Ganges river dolphin is the only aquatic mammal in certain riverine ecosystems on the Indian subcontinent. It is one of four species of freshwater dolphins found globally. Various anthropogenic activities including industrial and domestic pollution, boat traffic, reduced water flow and prey depletion mainly in the dry season, and housing/land development projects along the Turag River are potential threats for the long-term survival of the Ganges river dolphin. Our study shows the need for improved public policies aiming at the conservation of this endangered dolphin species and for programs of environmental education to raise the awareness of local residents regarding their land and its fishes and dolphin. A wide study is straightway essential in the Turag River system for conservation of the species as it is endangered (A2abcde) in IUCN Red List. River dolphins need to be considered in the valuation of impacts of river water improvement plans.

Knowledge Management: Journal