Credit: Giulian Frisoni, Flickr.

Warming, more acidic oceans are threatening marine species all over the world. The effects of global warming are far reaching, and our plates are no exception. According to a new study, increased temperatures shrank the number of fish hauled from the ocean by 4.1% between 1930 and 2010 — that’s without taking into account overfishing which is still the primary threat to fish stocks.

According to researchers at Rutgers University, the 4.1% decrease in fish stock directly attributed to global warming is equivalent to 1.3 million metric tons of fish.

“Fish populations can only tolerate so much warming,” said senior author Dr Olaf Jensen, also from Rutgers University.

“Many of the species that have benefited from warming so far are likely to start declining as temperatures continue to rise.”

As many as 56 million people living in coastal and island countries depend on fish to support their livelihoods. Worldwide, fish make up 17% of our protein intake, according to the United Nations.

The oceans are disproportionately affected by global warming because they act as both carbon and heat sinks. About a quarter of all the CO2 humans dump into the atmosphere is absorbed by the oceans, raising their acidity, which can lead to coral bleaching. However, oceans absorb more than 90% of the heat trapped by CO2 in the atmosphere — that’s about 150 times the energy humans produce as electricity annually. It follows that the oceans warm at a much higher rate than the atmosphere.

Besides hurting marine life, higher temperatures also increase sea levels, compromise coastal infrastructure, and disrupt global weather systems by intensifying storms, heavy rains, and marine heat waves.

Some regions have been hit harder than others. According to the authors of the new study published in the journal Science, ecosystems in the northeast Atlantic Ocean and the sea of Japan have seen fish populations decline by as much as 35% due to warming waters by over the last eight decades. Meanwhile, some regions have seen increased catches as the warming temperatures have increased the range of several species — such as the black sea bass off the Atlantic coast of the United States. However, the net effect is a decrease in global fish catch worldwide.

Like at the surface, ocean warming is not uniform so some regions are hotter than others. Fish are very sensitive to temperatures and will migrate in large numbers towards their preferred temperatures — that’s if the heat doesn’t kill them first or the food they depend on.

The authors warn that if the world doesn’t take urgent action to curb carbon emissions, ocean temperatures could rise by up to 3.2°C by the end of the century.

“We recommend that fisheries managers eliminate overfishing, rebuild fisheries and account for climate change in fisheries management decisions,” said Dr Chris Free, a University of California, Santa Barbara scientist who led the research.

“Policymakers can prepare for regional disparities in fish catches by establishing trade agreements and partnerships to share seafood between winning and losing regions.”