Farmed salmon gets high marks on environmental performance

Environmental activists have hurt the reputation of farmed salmon in this part of the world but another scientific investigation has confirmed what salmon farmers have been saying all along – salmon is environment friendly. In fact, it’s better than even the most sustainable animal protein farmed on land, chicken, says a new study from a Washington, DC-based institution.

“Many other people have found the salmon results surprising. Unfed mariculture, like oysters, has generally been recognized as resulting in low emissions and resource use compared to other foods, but few people seem to think of salmon as having environmentally sustainable attributes,” said Jessica Gephart, Assistant Professor, Environmental Science at American University.

 She and her study team looked at how much “blue foods” (fish and other aquatic foods) contribute to “stress” on the planet via their emissions of greenhouse gas, nitrogen and phosphorous, and their use of freshwater and land.

The study found that farmed and wild salmonids (trout and salmon) are similar in their CO2 emission, with farmed having 5,101 to 5,410 kilograms of CO2 equivalent per tonne compared to wild’s 6,881.   

Farmed and wild salmonids similarly ranked low on the list of the biggest sources of nitrogen and phosphorous, elements that cause algal blooms when in excess. To put this in context, shellfish and seaweed are the lowest on the list – 9th and 10th respectively among 10 named farmed blue food – because they remove nitrogen and phosphorous more than they release. Farmed and wild salmon and trout rank 7th.

The study, published in Nature on Sept. 15, also found that farmed trout and salmon use the least water and land among the farmed blue foods. Tilapia was the highest user of these resources.

“This is not to say there are no environmental concerns related to salmon farming, but for the environmental pressures we considered (greenhouse gas emissions, nitrogen and phosphorus emissions, land use, and freshwater use) the fact that it is mariculture means low on-farm land and water use and it has become quite efficient at feed utilization, allowing it to perform well compared to many other farmed aquatic foods,” said Gephart.

Feed production was identified as the source of more than 70 percent of emissions for farmed blue foods, while in wild capture fisheries, the biggest source is fuel.

Feed has to improve if aquaculture is to reduce its environmental impact, says the study. “We find feed conversion ratios (FCRs) represent the strongest lever, wherein a 10- percent reduction results in a 1– to 24 percent decrease in all stressors,” said the authors. 

Innovations to improve FCR could come via selective breeding, genetic improvements and high-quality feeds, the authors suggested.