Food footprints compared

Maria Burke

Food production is a leading cause of environmental degradation globally, according to Australian researchers who examined the environmental pressures surrounding farmed chicken and salmon. Efforts to reduce the environmental footprints of these industries should focus on feed ingredients, they say.

In the study, Caitie Kuempel and her team from the Australian Rivers Institute compared the environmental footprint of farming broiler chickens and salmonid species (salmon, marine trout and Arctic char) to identify opportunities to reduce environmental pressures. They mapped cumulative pressures including greenhouse gas emissions, nutrient pollution, freshwater use and land/sea-scape disturbance.

The team found that the food fed to farmed chicken and salmon accounts for 78% and 67%, respectively, of their environmental impacts (Current Biol., doi: 10.1016/j.cub.2023.01.037). Global chicken production is over 55 times greater than salmon in terms of protein weight but disturbs only nine times more area than salmon farming. In these terms, chicken farming is also more efficient than salmon farming when it comes to nutrient pollution (only 20 times higher) and greenhouse gas emissions (38 times higher). But less efficient in its freshwater use (135 times higher).

The footprints of both sectors were found to be extensive, but 95% of pressures were concentrated into a very small geographical area. The large overlap in the location of these pressures is primarily due to shared feed ingredients, the team says. Efforts to reduce environmental footprints should focus on food ingredients and learn from areas of high environmental efficiency. ‘Understanding where and how much environmental pressure different animal products exert is critical to designing effective food policies that promote sustainability,’ says Kuempel.

The result that the impacts are primarily due to feed is no surprise, says Ray Hilborn of the University of Washington, US, who expected them to be even higher. ‘I was surprised that, per unit of edible flesh, chicken was estimated to have a lower impact than salmon since my understanding is that salmon are more efficient at converting feed to flesh and most impacts come from feed.’

He suspects the result arose because salmon rely more on fishmeal and fish oil than chicken, and the authors’ methods of calculating ‘environmental pressure’ from fishmeal and fish oil, and crop production are totally different. He thinks they ‘grossly overestimate’ the impact of fisheries on marine ecosystems compared with growing crops on land.

Meanwhile, Frank Asche of the University of Florida, US, points out that it’s not surprising that food ingredients are grown in the same geographical areas given that most crops are grown in large quantities in only a few places due to soil quality and microclimate.