World’s oceans hold 30 times more fish than believed

Pew research by an international team of marine scientists suggests that the global biomass of fish is 30 times more than the accepted estimate, contradicting previous beliefs about the biomass of fish in the world’s oceans.

The team investigated mesopelagic fish that tend to dominate the world total fish biomass. Mesopelagic fish are open-sea species that occupy the mid-depth of the oceans from 200 metres to 1,000 metres below the surface.

They are small, often migrate to the surface at night, and have remarkable senses – in vision and in sensing pressure and motion – which enables them to avoid nets and fishing gear.

In a report in Nature Communications, the scientists say they had not been able to accurately estimate the biomass of fish in the past because of the difficulties in sampling and the fact that available estimates were based on false premises.

To overcome these problems, the researchers analysed acoustic observations collected during the Malaspina 2010 Circumnavigation Expedition. Their calculations showed that the previous estimate needed to be revised to a higher biomass of at least one order of magnitude.

This means there could be more than 3,000 million tonnes of mesopelagic fish in the ocean – a stock still untouched by fisheries and possibly increasing because of the decline of their main predators, tuna and swordfish.

Read the full article here.