Gangetic Dolphins Shift Habitat Following Vikramshila Setu Span Collapse: WCT Study
By Avijit Biswas
Bhagalpur, Bihar, India: A significant increase of motorized boat traffic including ferry barges and other vessels in river Ganga following collapse of suspended span of Vikramshila Setu located at Barari Ghat in Bhagalpur district of Bihar in recent past, it has been found led to displacement of endangered Gangetic dolphins from sizeable pre collapse distribution areas in stretch of river Ganga located close to the bridge.
A preliminary impact assessment undertaken by Wildlife Conservation Trust (WCT) after collapse of suspended span, has corroborated displacement of endangered species from their pre collapse distribution areas.
A suspended span between pillars no three and four of Vikramshila Setu connecting southern and northern parts of river Ganga here collapsed and fell into river Ganga on intervening night of May 3 and 4. The collapse site is located in stretch of river that constitutes Vikramshila Gangetic Dolphin Sanctuary (VGDS).
More than 50 Kilometer stretch of river Ganga extending between Sultanganj and Kahalgaon in Bhagalpur district was notified as dolphin sanctuary in August, 1991 by government of Bihar under Wildlife (Protection) Act, 1972 primarily for protection and conservation of endangered Gangetic dolphins, it may be mentioned.
Entrusted by forest department for impact assessment of bridge collapse on dolphin population, a three- day survey for the purpose was undertaken by WCT team from May 24. The WCT preliminary impact assessment report submitted to forest department recently has expressed possibility of various indirect impacts on dolphin population due to increased traffic of local motorized country boats, other vessels and ferry barges in river following closure of the bridge.
Rise in underwater noise level in river particularly had an adverse effect on dolphin population. The report has also expressed possibility of adverse effect on birds due to high noise level in river because of increased boat traffic. The report has stated about possible adverse effect on endangered and vulnerable bird species like Indian Skimmers and River Terns generally found nesting in mid channel islands during months of May and June.
In regards to dolphins, the WCT preliminary impact assessment report has mentioned increased boat traffic leading to high underwater noise, the endangered species were displaced from their pre bridge collapse distribution areas. The total net aerial displacement was calculated to be around 5.46Km and net linear displacement almost 9 km along river by WCT survey team indicating a 10% temporary habitat loss of dolphins in 50Kms sanctuary area. The report has mentioned to avoid disturbances it is likely dolphins have shifted to new habitats along downstream and also upstream.
Ashutosh Raj, Divisional Forest Officer (DFO), Bhagalpur, confirmed WCT preliminary impact assessment report findings have mentioned about temporary displacement of dolphins from their pre collapse distribution areas. The DFO however informed there are indications after temporary loss of habitat the dolphins have started returning to their original habitat. To substantiate his point the DFO said the area near a sand bar located in stretch of river between Barari Ghat and Engineering College used to be hotspot of dolphins prior to bridge collapse.
However, dolphin citing in the area had become rare after boat traffic in river increased considerably following bridge collapse. The citing of dolphins again in the area of late indicates the displaced endangered species are gradually returning to their original habitat, he added.
The DFO informed in light of WCT report he has written to chief wild warden on the issue of noise monitoring of boats and other vessels operating in sanctuary area. Taking note of the fact noise level more than 65 to 70 kHz could adversely affect ability of dolphins to echolocate, the department looks forward towards sound monitoring of boats and other vessels, he added.
Dr Nachiket Kelkar, Head Riverine Ecosystems and Livelihoods Programme, WCT, under whose guidance the preliminary impact assessment study was conducted said overlapping of high noise created due to increased boat traffic after bridge collapse with known hearing range of Gangetic dolphins led to their temporary habitat loss.
However, dolphins are likely to return to their original local distribution hotspots with rise of river water level and reduction of boat traffic in river, he said. Talking about impact on other species Dr Kelkar said because of high noise level in river possibility of reduced nesting activity by shorebirds on islands located in downstream of the river close to the bridge cannot be ruled out.
Further hydrological, acoustics and camera data are being analyzed presently for final impact assessment of bridge collapse on Gangetic dolphins, he informed. However, Dr Kelkar categorically said it is unlikely there was any adverse effect on Gangetic dolphins and other riverine wildlife species due to collapse of bridge structure and presence of debris in river.
Taking into consideration water level of river at the time bridge structure collapsed and fell into river, there is remote possibility of displacement of debris of collapsed structure downstream in the river, he added.
The findings of a similar survey undertaken in past by WCT after a portion of under construction bridge over river Ganga between Sultanganj and Aguwanighat in Bhagalpur district collapsed and fell into river in 2023, also revealed there wasa no adverse impact on Gangetic dolphins due to collapse and presence of debris in river.
The increased traffic of boats and other vessels in river following recent incident of bridge collapse primarily triggered temporary habitat loss of dolphins, the preliminary impact assessment report has underlined.
The boat traffic in river it may be mentioned has reduced to some extent after damaged Vikramshila Setu was opened for traffic in recent past bridging the gap created due to collapse of suspended span by belly bridge. However as per information, for permanent repair a plan for closure of the bridge for three months is under active consideration of the state government. There could be surge in river boat traffic once again following long time closure of the bridge, it is anticipated.
About the Author
Avijit Biswas is a former reporter with the Hindustan Times, Patna Edition, based in Bhagalpur. He has more than 25 years of experience covering politics and other key beats across eastern Bihar. Known for his in-depth ground reporting and strong grasp of regional issues, Biswas has closely followed political developments and social trends in the region, earning credibility for accurate and balanced journalism. Avijt may be contacted at biswasavijit@yahoo.com
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