Ivo da Costa, a Ph.D. student at the University of Porto, subdues a blue shark, which will be fitted with sensors to study how ocean oxygen levels affect its behavior. W. CORNWALL/SCIENCE
Warming oceans are running short of oxygen, and the fiercest marine predators are already feeling the effects.
Warren Cornwall, Science, February 2, 2023
Climate change is leaching oxygen from the ocean by warming surface waters. Two other climate-related threats to the seas—ocean acidification and marine heat waves—get more attention from scientists and the public. But some researchers believe deoxygenation could ultimately pose a more significant threat, making vast swaths of ocean less hospitable to sea life, altering ecosystems, and pushing valuable fisheries into unfamiliar waters. As global warming continues, the problem is sure to get worse, with disturbing forecasts that by 2100 ocean oxygen could decline by as much as 20%. Sharks—fast-moving fish that burn lots of oxygen, sit at the top of food chains and crisscross huge ocean expanses—should be sensitive indicators of the effects.
This is why a group of U.K. and Portuguese scientists took to the sea aboard Garcia Habas’s boat off the Canary Islands in November 2022.