How Many Fish are in the Ocean? Many More Than Was Thought

by Robert Cheney

in News

There are 10-30 times more fish in the ocean than was previously thought according to a new study published in the science journal Nature Communications.

To help understand, we must know the layers of the sea. The ocean away from the shore and above the bottom is called the pelagic zone. The pelagic zone is divided up into 5 additional zones with the traditional fishing areas focusing on the zone closest to the surface which is called the epipelagic zone. Sunlight dominates this zone which allows plants to live and where it was estimated that 90% of ocean life resides.

The mesopelagic zone is the next layer below the epipelagic and runs from 600-3300 feet down. This is considered the twilight zone due to the small amount of sunlight able to reach these depths. Previously, it was assumed that few fish reside in this zone because reports back from fishing trawlers indicated that fishing was slim when the nets were dropped to these depths.

Ocean Zones

Ocean Zones

Mesopelagic fish include the abundant lanternfish, the sabretooth fish and the barreleye.

Lanternfish are about 6 inches long and make up more than 50% of the fish in the mesopelagic zone.

Lanternfish are about 6 inches long and make up more than 50% of the fish in the mesopelagic zone.

An accurate census of the number of fish in this zone was never undertaken until recently when University of Western Australia Professor Carlos Duarte led a 7 month circumnavigation of the globe in the Spanish research ship Hesperides. They used echo-sounding measurements during the day to measure the quantity of sea life in depths of 200-3000 feet.

What they found was that 95% of the fish in the ocean reside in the mesopelagic zone and therefore untouched by fishermen. So, what about the fishermen reporting lackluster hauls from these depths? Because of the lack of light at these depths, these fish develop larger eyes and are more pressure-sensitive and are able to discern nets from up to 15 feet and simply avoid them.

The previous estimate of 1,000 million tons of biomass in this zone has been revised upward to in excess of 10,000 million tons.

So, 95% of the sea life is out of range of commercial fishermen and will remain that way unless newer fishing techniques are developed.

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