Researchers from the University of British Columbia (UBC) looked at the availability of four nutrients – calcium, iron, protein, and omega-3 fatty acids – in a high carbon emissions and low mitigation scenario.
They found that the availability of all four nutrients is projected to decrease in future, with calcium the hardest hit, with a predicted decline of 15 to 40% by 2100.
“Low-income countries and the global south, where seafood is central to diets and has the potential to help address malnutrition, are the hardest hit by the effects of climate change,” said first author Dr William Cheung, professor and director of the UBC Institute for the Oceans and Fisheries. “For many, seafood is an irreplaceable and affordable source of nutrients.”
Nutrient declines driven by falling fish populations
The researchers examined historical fisheries and mariculture databases to discover what quantities of key nutrients were available in the past, using predictive climate models to estimate future figures.
Calcium was the nutrient worst affected, with a predicted decline of 15 to 40% by 2100 under a low and high emissions scenario, respectively, while omega-3 was projected to experience a decrease of between 5 and 25%. These declines are largely due to decreases in the quantities of pelagic fish available for catch, the authors wrote in Nature Climate Change.
“Small pelagic fish are really rich in calcium, so in areas of the world where people have intolerances to milk or where other animal-sourced foods, like meat and dairy, are much more expensive, fish is really key to people’s diets,” said senior author Dr Christina Hicks, professor at Lancaster University.
“In many parts of the world, particularly low-income countries across the tropics, fish supply nutrients that are lacking in people's diets.”
Lower-income nations hardest hit by seafood-sourced nutrient declines
The availability of all four nutrients from tropical waters of lower-income nations, including Indonesia, the Solomon Islands, and Sierra Leone, is projected to decline steeply by the end of the century under a high emissions scenario, compared with minimal declines in higher-income, non-tropical waters, including those of Canada, the US, and the UK.
Globally, the researchers projected that seafood-sourced nutrient availability would decrease by 4 to 7% per degree Celsius warming.
However, for lower-income countries across the tropics, including Nigeria, Sierra Leone, and the Solomon Islands, the projected decline was two to three times this global average, at nearly 10 to 12% per unit of warming.
“This research highlights the impact of every degree of warming,” said Cheung. “The more we can reduce warming, the fewer risks to marine and human life.”
While seafood farming could contribute more nutrients in the future compared with current levels, the researchers projected that these increases would not compensate for the loss from fisheries. Under a high emissions scenario, any gains in the availability of nutrients from seafood farming before 2050 would be lost by 2100.
“The primary reason for this is climate change, which is also a significant threat to seafood farming, leaving us with a growing nutritional deficit,” said co-author Dr Muhammed Oyinlola, a postdoctoral fellow at the UBC’s department of zoology. “Seafood farming alone cannot provide a comprehensive solution to this complex issue.”
Adaptations to increase nutrient availability from seafood ‘limited in effectiveness’
Certain types of fish, including anchovies and herring, are packed with nutrients but often used for fish meal and fish oil because these nutrients also promote fish growth. Similarly, many countries retain only select parts of a fish for sale.
The researchers highlighted potential adaptations to increase nutrient availability from seafood by retaining more of these nutritious fish for local human consumption, as well as reducing food waste in fisheries production and consumption by using all parts of a fish including the head and fins.
However, Cheung added: “The future development of seafood supply needs to consider the nutritional security of vulnerable groups, not just economic benefit. But there’s a limit to how effective these interventions are, so it’s important to limit global warming as much as possible.”
