The loss of oxygen from the world’s ocean is increasingly threatening fish species and disrupting ecosystems, a new International Union for Conservation of Nature (IUCN) report warns.

Ocean oxygen loss, driven by climate change and nutrient pollution, is a growing menace to fisheries and species such as tuna, marlin and sharks, according to the report released on Saturday at the COP25 UN Climate Change conference in Madrid.

The review report “Ocean deoxygenation: Everyone’s problem” is the largest peer-reviewed study so far into the causes, impacts and possible solutions to ocean deoxygenation. Ocean regions with low oxygen concentrations are expanding, with around 700 sites worldwide now affected by low oxygen conditions – up from only 45 in the 1960s. In the same period, the volume of anoxic waters – areas completely depleted of oxygen – in the global ocean has quadrupled, according to the report.

The report is available here