Warming oceans are dramatically reducing fish populations, putting the ecosystem as well as income and food for millions of people at risk, as per a new study in the journal Science. The report – titled ‘Impacts of historical warming on marine fisheries production’ – found that the maximum sustainable yield that human beings could harvest from the oceans decreased by 4.1 per cent from 1930 to 2010, with five eco-regions experiencing losses of 15 to 35 per cent.

The study looked at sustainable catches, a measure that quantifies the amount of food that can be repeatedly harvested from a base population of fish. Using a data set of 235 fish populations in 38 eco-regions across the globe, the researchers could figure out the locations of fish and how they reacted to environmental effects like changing water temperatures. They then compared it to data that showed how the ocean temperatures had changed over time in various regions since some parts of the ocean had warmed faster than others. Their analysis showed that fish populations in the colder regions fared better than those in warmer areas. Overfishing made the problem worse.

Sea food is responsible for 17 per cent of the global population’s intake of animal protein and about 70 per cent for those living in some coastal and island countries. Around 56 million people worldwide are estimated to rely on marine fisheries. As the report states, ‘fisheries provide food and support livelihoods across the world.’ While overfishing and poor management have contributed to the problem, climate change is exacerbating it and is leading to a major depletion of this food source and resulting in a significant decline in fish populations. Some fish species may also get wiped out. For example, in the northeast Atlantic Ocean and the Sea of Japan, fish populations have declined by 35 per cent over the period of this study.

Warming ocean temperatures are a direct result of global warming since they have absorbed 93 per cent of the heat trapped by greenhouse gases, emitted due to human activities. As reported earlier this year, scientists have found that the world’s oceans are heating up to 40 per cent faster on average than previous estimates. That doesn’t bode well for living populations on land and in the oceans.