India, Oct. 31 -- THE HILSA (Tenualosa ilisha) is more than a fish. It anchors festival meals across the Ganga-Brahmaputra-Meghna delta and sustains millions of small-scale fishers and traders. Of late, warming seas, a stressed delta and national borders that cut across its range are putting the fishery under growing pressure. A regional fisheries review finds that rivers accounted for 94 per cent of Bangladesh's hilsa catch between 1956 and 1962, while the sea supplied just 6 per cent. Today, the balance has reversed. Data from Bangladesh's Department of Fisheries shows about 72 per cent of the catch comes from marine waters, compared with 28 per cent from rivers and estuaries.

A scientific review of the species adds that riverine catch...