Brahmaputra River Islands

Brahmaputra River Islands: Emerging Corridors for Tigers

Brahmaputra River Islands

The Brahmaputra valley acts as a vital link for wildlife populations by facilitating the movement of various large mammals between numerous Protected Areas in central Assam. Key tiger habitats in the flood plains of the Brahmaputra include Orang NP, Laokhowa and Burachapori Wildlife Sanctuaries and Kaziranga NP. Nameri National Park and Pakke Tiger Reserve are located at the Northern end of the Brahmaputra basin, along the border of Assam and Arunachal Pradesh. Kaziranga and Orang National Parks support the largest extant tiger populations in north-east India and Kaziranga NP has been recognized to serve as a ‘source site’ for the entire region. The Brahmaputra ecosystem is not only a stronghold of tigers, but is also home to a plethora of other wildlife species, several of which only occur lowlands abutting the Himalayan ranges.

Photographic evidence from camera traps has revealed that tigers may traverse long distances in the Brahmaputra Basin, using river networks and even moving through human dominated areas. For example, in 2013, a tiger was documented to have moved from Kaziranga National Park to Nameri National Park. The tiger is believed to have covered an approximate distance of 90 kilometers -swimming across the Brahmaputra River, using river islands, moving through a vast expanse of agricultural land, and even fording the busy National Highway 52. The persistence of tigers in this landscape requires that viable meta-populations exist; animals can successfully move between various PAs and habitat patches via the Brahmaputra River Islands and through the agricultural matrix.

Connectivity between various forest fragments that support tigers has drastically reduced in recent decades on account of increasing human pressure and growing habitations along the river bank and on the islands. In addition, flood-dynamics of the Brahmaputra River result in annual creation of new river islands, even as some existing islands are washed away. Habitat integrity and connectivity has also been compromised by increasing human pressure on the Laokhowa and Burachapori wildlife sanctuaries in recent decades. Recognizing these challenges, WWF India’s conservation program in the North Bank and Kaziranga Karbi Anglong Landscapes has emphasized the maintenance of habitat connectivity between forest patches in the Brahmaputra river valley.

Brahmaputra River Island Survey
To investigate the use of Brahmaputra islands by tigers and other wildlife, and document the extent and intensity of human use in these areas, WWF India and the State Forest Department collaboratively initiated a series of island surveys in 2010. These surveys were designed to assess functionality of the riverine islands as corridors for dispersing the wildlife (primarily, carnivores and prey species) from Kaziranga NP to proximate habitat patches.River Bank

Surveys encompassed the islands on the Brahmaputra River between the eastern end of Kaziranga NP and western end of Orang NP. Thus far, WWF India has carried out the survey in four phases (2010-11, 2012-13, 2015-16 and 2016-17). The first phase covered the islands between Laokhowa and Burachapori WLS and Kaziranga NP. In the second phase, the islands between Orang NP and Laokhowa and Burachapori WLS were covered. During the third phase in 2015-16, the survey covered portions of three major tributaries of the Brahmaputra i.e. JiaBhoroli, Borgang and Buroi which serve as connecting links between Kaziranga NP – Nameri NP, and Kaziranga NP – Behali Reserve Forest. Concurrently, we also carried out a socio economic assessment of human settlements on the river islands to map and understand anthropogenic pressures and threats. The most recent survey was conducted between November 2016 and January 2017 from eastern point of Kaziranga NP to Kolia Bhomora bridge. During this phase, camera trap sampling was carried out for a 20 day period along with sign surveys. 14 pairs of camera traps were used in 14 different islands to record photographic evidence of animal use.

Sign surveys were an important part of the river island surveys. Such sign surveys involved sampling islands on foot transects to detect indirect evidence for the presence of wildlife (eg. tracks, spoor, scrapes, scent markings). Visual detections of mammals were also recorded. Survey effort (transect length) varied between 0.5 and 2km, depending on the size of the islands, and other field conditions including accessibility.

Results and Outcomes
During the Brahmaputra River Island Survey, evidence of tiger presence was detected in 18 of the river islands, including direct sighting of a tiger in Hatibalu Chapori of Bishwanath Range of Kaziranga NP. During the second phase of the survey, presence of tiger cubs was also recorded in Kartika Chapori. Evidence of breeding tigresses on the islands may be indicative of the fact that some islands may in fact lie within the territorial boundaries of some tigers.

In addition to tigers, the presence of other carnivores was also detected on most of the islands. In the 2016 camera trap survey, tigers, rhinos, fishing cat, jackal, sambar, hog deer and water buffalo were photocaptured, while water buffalo, swamp deer, elephant, sambar, wild boar, and hog deer were sighted on transect surveys.

Of the 45 river islands surveyed, more than 50 % had human habitations. People belonging to five different communities are found to have occupied these islands, mostly on a seasonal basis, with livestock rearing and agriculture being their mainstay. Incidents of human wildlife conflict are very common in the islands, mainly by way of crop depredation by large herbivores (elephants, deer and wild boar) and livestock depredation by tigers and leopards. However, there has been no systematic documentation of conflict by Government agencies.

The Way forward
The Brahmaputra River Island surveys revealed the presence of several endangered mammals on islands. These islands serve as stepping stones and may provide connectivity between some of Assam’s most important PAs.

The ephemeral nature of river islands and their relative inaccessibility has resulted in being neglected from both administrative and wildlife management perspectives. Thus, jurisdiction and law enforcement needs to be strengthened to ensure protection of these ever important wildlife habitats that also serve as vital corridors. Information generated through these series of surveys has been used to influence and inform decision making for proper protection and management of this unique ecosystem, and there is increased patrolling by forest guards on a number of islands adjacent to Kaziranga National Park. In the coming years, WWF India in collaboration with various Government Departments intends to take up initiatives to ensure the protection and management of the much crucial islands of the Brahmaputra River. Efforts will also be undertaken to reduce anthropogenic pressure in these islands by taking steps to reduce impacts of local communities on wildlife habitats, and also garner their support for the conservation.

– Courtesy: WWF India