Study shows plenty more fish in ocean

Mesopelagic fish make up the majority of the world’s total fish biomass. |Picture: UWA Oceans Institute
Mesopelagic fish make up the majority of the world’s total fish biomass. |Picture: UWA Oceans Institute

A team of UWA marine scientists studied mesopelagic fish, which occupy the mid-depth of the world’s oceans, from 200 metres to 1000 metres and dominate the world’s total fish biomass.

Their impressive sensorial capacity allows the small fish to avoid nets and fishing lines.

The study, published in Nature Communications, contradicts what experts have previously understood about the overall number of fish in the world’s oceans.

Professor Carlos Duarte said there had been difficulties with sampling in the past, which meant an accurate estimate of the biomass was hard to determine.

To overcome these difficulties the researchers collected acoustic observations during a 2010 expedition that showed the previous estimate needed to be revised.

‘This means there could be more than 3000 million tonnes of mesopelagic fish in the ocean, a stock still untouched by fisheries and possibly increased due to the decline of their main predators, tuna and swordfish,’ Professor Duarte said.

Professor Susana Agusti, a research professor with the Oceans Institute and School of Plant Biology, said the mesopelagic fish must play a key role in the healthy biogeochemical cycles of the oceans.

‘Their behaviour accelerates the transfer of carbon from the ocean surface to the depths,’ Professor Agusti said.

The $23 million Malaspina Expedition, led by Professor Duarte, involved more than 400 scientists and researchers on two ships circumnavigating the globe to investigate the health of the world’s oceans.