Factory-farmed fish, pigs and poultry are consuming 28 million tonnes of fish a year, or roughly six times the amount of seafood eaten by Americans, according to new research.
A nine-year study by the University of British Columbia has found that 90 per cent of small fish caught in the world's oceans every year such as anchovies, sardines and mackerel are processed to make fishmeal and fish oil.
They are used as a cheap feed for aquaculture (including farmed Atlantic salmon, prawns and trout), poultry, pigs and animals bred for the fur industry.
The study's findings, to be published next month, warn this use is unsustainable, given current rates of global overfishing and increasing threats to global food security.
University of Columbia senior researcher Jacqueline Alder said: "Society should demand that we stop wasting these fish on farmed fish, pigs, and poultry.
"Although feeds derived from soy and other land-based crops are available and are used, fishmeal and fish oil have skyrocketed in popularity because forage fish are easy to catch in large numbers and, hence, relatively inexpensive."
Dr Alder, who was previously a researcher at James Cook University in Townsville, warns that the excessive harvesting of forage fish is "squandering a precious food resource for humans and disregarding the serious overfishing crisis in our oceans".
According to the study, small forage fish account for 37pc, or 31.5 million tonnes, of all fish taken from the world's oceans each year.
Of this amount, 90pc is processed into fishmeal and fish oil.
Current figures show 46pc of fishmeal and fish oil is used as feed for aquaculture, 24 per cent for pig feed and 22pc for poultry.
The study estimates that pigs and poultry around the world consume more than twice as much seafood as the Japanese eat.
The farmyard animals eat more than six times the amount consumed in the United States.
Fisheries targeting forage fish are concentrated in four areas of the world the western coast of South America, northern Europe, the Atlantic seaboard of the US, and Alaska.
Scientists have raised concerns that a 50pc increase in global aquaculture in the past 10 years will seriously affect marine ecosystems already under threat from acidification of the oceans caused by climate change.
Species dependent on forage fish include penguins, gulls, cormorants, puffins, dolphins and right whales.
The study says little is known about the role of forage fish in marine ecosystems and few management plans exist for sustainable fishing of these key marine food-web species.
Neither are there plans to to deal with a growing global human demand for fish-oil supplements, thought to reduce the risk of dementia.
The US-based Pew Institute for Ocean Science Institute, which funded the research, plans to set up a global taskforce of leading scientists and fisheries policy experts to find new ways of making forage fisheries more sustainable.
The institute's executive director, Dr Ellen Pikitch, said: "It defies reason to drain the ocean of small, wild fishes that could be directly consumed by people in order to produce a lesser quantity of farmed fish."
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