Hilsa (Tenualosa ilisha) catches in the Bay of Bengal have shifted from rivers to the sea, and from West Bengal towards Gujarat. Warming seas, weaker monsoon flows, rising estuarine salinity, dams and the overharvesting of juvenile fish are disrupting the species’ upstream spawning migration. Uncoordinated fishing bans across India, Bangladesh and Myanmar mean that fishing pressure moves across borders instead of falling. The authors argue for an ecosystem approach to fisheries management, with synchronised closures, joint stock assessments, shared monitoring and protected migration corridors.