Sea cucumber weighing around 500 kg and valued at Rs 10 lakh, meant to be smuggled to Sri Lanka, was seized at Mandapam near Rameswaram on Sunday, Marine police said.
A boat used to smuggle the sea cucumber has also been seized, they said.
The occupants of the boat escaped after seeing the police personnel.
Sea cucumbers, classified as endangered species and their harvest banned under the Wildlife Protection Act, are in demand in South-East Asian countries.