Aquaculture uses far more wild fish than previously estimated, study finds

These findings call into question long-held assumptions about the sustainability of the rapidly growing aquaculture industry and provides a range of plausible estimates for its impact on wild fish populations.

The research, led by an international team of scientists from the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science, Oceana, and New York University, provides a reassessment of the "fish-in:fish-out" (FI:FO) ratio for global fed aquaculture -- a key metric used to evaluate the efficiency and sustainability of aquaculture.

The findings indicate that the ratio of wild fish inputs to farmed fish outputs is 27% to 307% higher than previous estimates, ranging from 0.36 to 1.15 compared to an earlier estimate of only 0.28. When accounting for wild fish mortality during capture and excluding unfed aquaculture systems, the ratio rises even further to 0.57 to 1.78. For carnivorous farmed species specifically, like salmon, trout, and eel, wild fish inputs likely exceeded twice the farmed fish biomass produced.

"Our study reveals that the aquaculture industry relies more heavily on wild fish extraction than previous research has suggested," said Spencer Roberts, a doctoral student at the Rosenstiel School in the Department of Environmental Science and Policy, and lead author of the study. "This demonstrates the scale at which aquaculture could be impacting marine ecosystems."

The research team's approach included accounting for previously overlooked sources of wild fish in aquaculture feed, such as trimmings and byproducts from wild-caught fish. They also incorporated collateral fishing mortality, including "slipping" -- a practice where unwanted catch is released but a large portion of the animals often do not survive. By analyzing multiple industry-reported datasets, the team provided a range of estimates and highlighted uncertainties in current reporting practices.

"This research shows that the assumptions we have made about carnivorous aquaculture have been too optimistic, and is another reason to think strategically about the kinds of aquatic species it makes the most sense to mass produce," said Jennifer Jacquet, a co-author of the study and a professor in the Department of Environmental Science and Policy at the Rosenstiel School

The study also examined the environmental trade-offs involved in reducing wild fish use in aquaculture feed. The researchers found that widely-cited estimates of declines in wild fish use from 1997-2017 would require a more than five-fold increase in the use of terrestrial crops over the same period.

Patricia Majluf, Ph.D. a senior scientist with Oceana in Peru, which is home to the largest fishmeal fishery in the world, notes that the growing use of by-products and trimmings has not phased out the capture and use of whole wild fish in feeds for aquaculture. "The offshore aquaculture industry is growing so rapidly that the wild-caught fish is not being replaced in their feed. Instead, other feed sources are just supplementing wild fish use," states Majluf.

The findings have significant implications for policy-makers, investors, and consumers. The study calls for more comprehensive and transparent reporting of feed ingredients in the aquaculture industry and suggests that policies promoting aquaculture expansion on sustainability grounds should be reconsidered.

Matthew Hayek, an assistant professor in the Department of Environmental Studies at New York University and the study's corresponding author, stated "It's crucial that we have a more complete understanding of the industry's impact on both marine and terrestrial ecosystems and reduce these uncertainties." He emphasizes that even with the wide uncertainty ranges reported, the impacts are still larger than previously reported, and "most offshore finfish aquaculture facilities produce carnivorous fish, and therefore are responsible for depleting far more fish from the ocean than what they can produce."

The researchers stress that while their study provides a more comprehensive view of aquaculture's environmental impacts, further research is needed to fully understand the sector's effects on issues such as nutrient pollution, habitat destruction, and the spread of diseases to wild fish populations.

As the demand for seafood continues to grow worldwide, these findings underscore the urgent need for more transparency in fish farming.

Funding support for this study was provided to Spencer Roberts and Matthew Hayek from the Grace Communications Foundation.