Bhubaneswar, Nov 19 (IANS): Thousands of endangered Olive Ridley turtles started congregating in the shallow coastal waters of Odisha ahead of their mass nesting season, official said Tuesday.

The turtles were spotted gathering near the famous Gahirmatha marine sanctuary in the district of Kendrapada, divisional forest officer Kedar Kumar Swain told IANS.

More than half a million Olive Ridley turtles arrive and congregate in the shallow coastal waters of the state through October-November, climb ashore and nest between December and March. Most the hatchlings emerge by May.

Gahirmatha, 170 km from the state capital Bhubaneswar, is one of the world's largest turtle nesting sites. Swain said many camps have been set up at the sanctuary to protect the endangered turtles.

More than 100 volunteers and officials have been engaged to ensure that turtles do not face any trouble or threat, he said.

The government imposed a seven-month fishing ban early this month, along 120 km of the state's 480-km coastline to protect turtles.

The authorities have also directed the trawlers and boatmen not to carry out any fishing activity within 20 km of the coast during the ban period, which will be effective till May 31.