About 35 members of the Bharath Makkal Katchi, including the party's state General Secretary Annadurai, were arrested when they left the town and were on way to the Jetty to board the boat kept ready for their journey.
They were demanding retrieval of the islet from the Sri Lankan government.
As the Centre failed to take any step in this regard, they were marching to occupy Katchatheevu and facilitate fishing by fishermen here, Annadurai said.