This post was originally published in Salmon Business.
Fish extraction and land use trade-off in aquaculture. Circle sizes represent the total production weight of each farmed species group by reported production for the year 2015. Terrestrial impacts are calculated by multiplying feed use data from Pahlow et al. (26) by land use data from Poore and Nemecek (44). Fishing impacts are assessed as a ratio of fished biomass input over farmed fish biomass output (FI:FO), calculated using our adjusted FI:FO method and Pahlow et al. (26) feed composition data.
A new study published in Science Advances has found that the global aquaculture industry, including salmon farming, may rely on significantly more wild-caught fish than previously estimated.
Led by scientists from the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science, the study challenges long-held assumptions about the sustainability of fish farming and suggests a substantial impact on wild fish populations.
Biomass ratios of wild fish mortality to farmed fish product (FI:FO) for salmon farming, delineated by cause and repeated using four different datasets. The leftmost column represents results of the FI:FO formula outlined by RW Hardy and used in Naylor et al. (14). Fish inputs not captured by this method are included in Naylor&al* and subsequent scenarios. Cuts represent previously unaccounted wild fish classified as trimmings and by-products. Collateral represents mortality from bycatch and slipping during capture. Sources are Naylor et al. (14), Tacon et al. (15), Monterey Bay Aquarium Seafood Watch (16–25), and Pahlow et al. (26).
The research revises the “fish-in” (FI) ratio—a key metric for measuring the efficiency of aquaculture. The study found that wild fish inputs into aquaculture are between 27% and 307% higher than previous estimates, with the ratio ranging from 0.36 to 1.15 compared to earlier estimates of 0.28. For carnivorous species like salmon, trout, and eel, the wild fish inputs often exceeded double the amount of farmed fish biomass produced.
“Our study shows that the aquaculture industry relies more heavily on wild fish extraction than previously thought,” said Spencer Roberts, the study’s lead author and a doctoral student at the Rosenstiel School.
The researchers accounted for previously overlooked sources, including wild fish trimmings and byproducts, and also highlighted the practice of “slipping,” where unwanted catch is released but often does not survive. The study calls for greater transparency and comprehensive reporting of feed ingredients used in aquaculture, warning that policies promoting aquaculture expansion on sustainability grounds may need reconsideration.
Jennifer Jacquet, a co-author of the study, emphasized that earlier assumptions about the sustainability of carnivorous aquaculture were overly optimistic. “This study highlights the need to rethink which aquatic species are most suitable for mass production,” she said.