Big fishes capable of reducing the carbon dioxide in Earth’s atmosphere!

When a fish dies in the sea it sinks to the deep depths, removing all the carbon components  it holds with it. This is a form of ‘blue carbon’ – It is a carbon captured stored by the oceans and coastal ecosystems.

“When the  fishes  are caught, they emit the carbon dioxide partly into the atmosphere  a few days or weeks after,” said Gaël Mariani, a PhD scholar at the University of Montpellier in France.

Mr. Mariani led a world-first study revealing how ocean fisheries have released at least 730 million metric tons of CO₂ into the atmosphere since 1950. An estimated 20.4 million metric tons of CO₂ was emitted in 2014, which is equivalent to the total annual emissions of 4.5 million cars.

The Co-author and Professor David Mouillot from the ARC Centre of Excellence for Coral Reef Studies at James Cook University (CoralCoE at JCU) said the carbon footprint of fisheries is 25% higher than previous industry estimates. In addition, “Fishing boats emit greenhouse gases by consuming fuel,” Prof Mouillot said. “And now we know that catching fish releases additional amount of CO₂ that would otherwise remain in the ocean.” Large fish such as tuna, sharks, mackerel and swordfish are about 10%  to 15% carbon.

“When these large fishes die, they sink rapidly,” Prof Mouillot said. “As a result, most of the carbon they posses is isolated and hidden at the bottom of the ocean for thousands or even millions of years. They are therefore carbon sinks – It is the amount of carbon which has never been estimated before. This is a  natural phenomenon, a blue carbon pump has been increasingly and greatly damaged by industrial fishing.

The authors also say the phenomenon has been overlooked until now specially  in  the areas where fishing is not a profitable business such as in the Central Pacific, South Atlantic, and North Indian Oceans. “Fishing boats many a times go to very remote areas with enormous fuel consumption even though the fish caught business in these areas are not profitable and fishing is only viable thanks to subsidies,” Mr Mariani said.

“The destruction of the blue carbon pump constituted by large fishes suggests new protection and management measures must be prioritized, so that more large fishes can remain a carbon sink and no longer be means of an additional CO₂ source,” Mr Mariani said. “And in doing so we further bring down CO₂ emissions by burning less fuel. We need to fish better,” Prof Mouillot said.