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Salmon farming industry must stop using wild-caught fish as feed, say Cambridge scientists

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An extra 6.1 million tonnes of seafood would be available for human consumption and 3.7 million tonnes of fish could be left in the sea each year if we ate the wild-caught fish currently used as feed in salmon farming, scientists have found.

Using fish by-products such as trimmings for salmon feed, rather than whole wild-caught fish would deliver major nutritional and sustainable benefits, according to a study co-led by scientists at the universities of Cambridge, Lancaster and Liverpool with Feedback Global, an environmental organisation.

A Scottish salmon farm
A Scottish salmon farm

Aquaculture is the world’s fastest growing food sector and often presented as a way of relieving pressure on wild fish stocks. But Atlantic salmon, and other aquaculture fish, are farmed using fish oil and meal made from millions of tonnes of wild-caught fish that is mostly food-grade.

The scientists’ examination of the Scottish salmon farming industry explored the data on fish nutrient content, fishmeal and fish oil composition and salmon production, while examining the transfer of micronutrients from feed to fish.

They found more than half of the essential dietary minerals and fatty acids available in wild fish are lost when these fish are fed to farmed salmon.

Dr David Willer, a researcher in the University of Cambridge’s Department of Zoology and first author of the paper, said: “Fish and seafood provide a vital and valuable micronutrient-rich food source to people worldwide, and we must make sure we are using this resource efficiently. Eating more wild fish and using alternative feeds in salmon farms can achieve this.”

Atlantic salmon
Atlantic salmon

The team examined alternative production scenarios in which salmon were produced using fish by-products alone, and added more wild-caught fish, mussels or carp for human consumption.

All of these scenarios produced a greater amount of seafood that was more nutritious than salmon, and left 66 to 82 per cent of feed fish in the sea.

Feedback’s Dr Karen Luyckx said: “If we want to feed a growing global population well and sustainably, we must stop catching wild fish to feed farmed fish. Until the salmon industry kicks its wild-caught fish oil and fishmeal habit, chefs and retailers should help citizens switch away from unsustainable salmon by offering ultra-nutritious mussels and small oily fish instead.”

More needs to be known about the source and species composition of fishmeal, say the authors of the study published in the journal PLOS Sustainability and Transformation, although there are positive signs that the use of plant-based feeds is growing.

Dr James Robinson, of Lancaster University, said: “Aquaculture, including salmon farming, has an important role in meeting global food demand, but nutritious wild fish should be prioritised for local consumption rather than salmon feed, particularly if it is caught in food-insecure places.

“Support for alternative feeds can help this transition, but we still need more data on the volumes and species used for fishmeal and fish oil, as this can show where salmon farming places additional pressure on fish stocks.”

Salmon for sale
Salmon for sale

Dr Willer added: “If we want to feed the growing global population well and sustainably, we must stop catching wild fish to feed farmed fish. There is an urgent need for the food industry to promote consumption of more sustainable seafood species - like mussels or carp - that don’t require other fish as feed.”

This research was funded by the Cambridge Philosophical Society, via a Henslow Fellowship to David Willer.

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