Karunanidhi said India had already made it clear that New Delhi does not consider them guilty and therefore it would take all legal and diplomatic steps for their release.
"Since the fishermen have been allowed time till November 14 for appeal in Supreme Court, the Centre should immediately contact Sri Lankan government and pave the way for the release of the convicted fishermen," he said in a statement here.
His daughter and Rajya Sabha MP Kanimozhi had taken up the matter in the Upper House during the UPA regime and then External Affairs Minister Salman Khurshid had assured of steps for protecting them "but there had been no sustained efforts by the Centre after that" following which they have given capital punishment, Karunanidhi said.
Pointing out at the unrest among fishermen in Tamil Nadu, he also said all the arrested fishermen were below 45 years of age with one of them aged 19 and expressed concern over the future of their families following the verdict.