During a survey conducted in 2010, only 130 bisons were spotted in the core area of the Trishna sanctuary spread over more than 164 sq km. But this year the number has risen to 145, a forest official said.
The 30 sq km Bison reserve was established in Trishna sanctuary a few years ago with funds from the Centre to preserve and protect the endangered species of Bison, locally known as Gaba or Gaur, he said.
"The Bison reserve aims at ecological restoration of existing natural habitats and migratory route of bisons, promotion of measures for mitigation of man-animal conflict in crucial habitats and strengthening measures for protection of bisons from poachers," state Forest Minister Jitendra Chowdhury said.
Grass has been cultivated in major habitats of bison in the Trishna core area as well as the National Park area, the official said.
Recently plantation of one species of Bamboo, locally known as Kaillai, which is a favourite food of Bison has been started to meet the need of food during the lean period, the official said.
Meanwhile, 7sqkm area of the bison reserve has been fenced off, good grazing land developed and a watch tower recently constructed for tourists, the official said.
Five more watch towers would be constructed in the area for tourists. This area, now covered with green grass, has emerged as natural grazing land for the bisons. It is known as Eden of Bisons.
Population of bison has been on the rise during last couple of years after the Indo-Bangla border adjoining the sanctuary was encircled with barbed wire fencing, the official said.
As many as nine new calves were noticed by the forest officials last month inside the core area, the official said. The minister said a few years ago poachers were very active and entered the sanctuary area from Bangladesh.
"However, the situation has changed and the population of the animal is increasing following erection of barbed wire fencing on the border line", the minister said. The team of forest protection force has also been strengthened, he added.