BHUBANESWAR: The number of Irrawaddy dolphins in Chilika has dropped to 145 from an estimated 156 last year and 158 in 2010, according to the latest census data. Dolphin census was conducted in the brackish water lake on Monday and Tuesday. Chilika, a Ramsar site (i.e. a wetland of international importance) since 1981, incidentally, has the largest lagoonal population of Irrawaddy dolphins in the world, ahead of Lake Songkhla in Thailand.