Past trends and future sustainability of feeding ‘fish to fish’

Not all fish from the sea go directly to our plates and the majority of aquatic protein (fishes, crustaceans, etc.) no longer comes from the wild. Aquaculture, also known as aquatic farming, now accounts for more than half of all global seafood production and is the fastest growing food sector on the planet. However, fed aquaculture species, like salmon and carp, use a limited and important natural resource from the wild: forage fish (e.g., anchovies, herrings, sardines).
Past trends and future sustainability of feeding ‘fish to fish’

‘Feeding fish to fish’ has been voiced as a sustainability concern because these small pelagic fish can play a large role feeding wild species, including whales, birds, and salmonids. Notably, several of the authors on our recently published paper, ‘Avoiding the Ecological Limits of Forage Fish for Fed Aquaculture’ (DOI: 10.1038/s41893-018-0077-1) in Nature Sustainability, have studied the dynamics and management of forage fish in great detail, but had not considered the role of aquaculture to overextend versus sustainably use forage fish into the future. We specifically wondered whether certain mitigating measures – some of which are already being implemented – on the fisheries AND farming side could prevent overextending the supply of forage fish as aquaculture continues to meet the ever-growing seafood demand.

Woman feeding fish
World Fish (CC0)

This simple, but powerful adjustment of accounting for multiple food sectors forced us to look at past and present fishing and feed-use trends and then model the relative contribution of plausible adjustments to avoid the upper limits of forage fish by mid-century. Three major aspect of the research emerged: (1) forage fish have been used in animal feeds since at least the 1960s, and agriculture still uses around 25%; (2) global reform of forage fish fisheries alone is not sufficient to meet future demands (but it does help); (3) not all animals cultivated by humans on land and water need forage fish to grow, like pigs, poultry, and carp, and removing forage fish from these diets offers large savings.

We ultimately conclude combined actions by fisheries, agriculture, and aquaculture can circumvent reaching the unsustainable limits of forage fish by 2050. However, if new conservation-based restrictions limit access to forage fish supply, climate change in fact reduces productivity, and/or seafood demand unexpectedly increases faster than anticipated (e.g., global adoption of pescetarian diets), the mitigating measures explored here would have to be adopted much more rapidly. These uncertainties thus speak to the importance of alternative feeds (e.g., algae) and continual improvements in animal efficiencies for a sustainable aquaculture future.

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