Significant Consequences for Biodiversity if Marine Protein were displaced by agricultural production

A recently published scientific review in Reviews in Fisheries Science & Aquaculture takes a detailed look at how global biodiversity would be affected if the protein currently supplied by marine capture fisheries had to be produced on land instead. The findings challenge many of the assumptions underpinning current sustainability debates. In particular, the review questions the common view that terrestrial protein sources—whether livestock or plant-based—necessarily represent a lower-impact alternative to fish. Instead, the evidence points to significant and far-reaching consequences for biodiversity if marine protein were displaced by agricultural production.

Land Use Requirements and the True Scale of Substitution

A key result from the study concerns the sheer land area required to replace marine-sourced animal protein. The authors estimate that substituting today’s marine capture protein with the current global mix of beef, pork, and poultry would require around 4.99 million km² of additional agricultural land. To put that into context, that is equivalent to 152% of all remaining intact Brazilian rainforest. The magnitude of this shift demonstrates how large an ecological footprint terrestrial protein production can have.

The review also considers more plant-based scenarios. Replacing all marine protein with grains would still require nearly 481,390 km², while substituting with soy would require about 230,230 km²—equivalent to 15% and 7%, respectively, of intact Brazilian rainforest. These figures are substantially lower than those for livestock, but still represent large-scale land conversion at a time when competition for land is intensifying and terrestrial ecosystems are already under considerable stress.

Comparing Biodiversity Risks: Agriculture vs. Fisheries

The review draws on IUCN Red List data to compare how many species are threatened by agriculture versus fishing. The difference is striking: 22,728 species are threatened by agricultural activity, compared with 2,143 species threatened by fishing. When expressed per unit of protein produced, agriculture threatens 63 species per million tonnes (MMT) of protein, while marine capture fisheries threaten around 24 species per MMT. In other words, agriculture poses 2.6 times the biodiversity risk per unit of protein.

These differences arise largely from how the two systems interact with ecological structure. Agriculture usually involves replacing entire native ecosystems with monocultures or grazing systems, affecting species throughout the lower trophic levels where biodiversity is highest. Fisheries, by comparison, primarily take biomass from higher trophic levels, leaving the base of the food web in place. It’s also worth noting that roughly 60% of global fishing effort uses gear that does not interact with the seabed. Even bottom trawling—commonly highlighted for its impacts—tends to occur in mobile sediment habitats that recover more rapidly when fishing pressure is well managed.

Implications for Aquaculture and Feed Formulation

For aquaculture, the review provides an important quantitative perspective on feed substitution. Completely replacing fishmeal with soy would require an additional 47,453 km² of agricultural land. Even removing only whole-fish reduction products (while retaining trimmings) would still require over 20,000 km². This highlights the spatial and biodiversity implications of simply shifting from marine-derived nutrients to terrestrial ones. In essence, strategies that seek to reduce the footprint of marine ingredients risk transferring impacts onto land—where biodiversity losses are both more advanced and often less reversible.

From a feed-formulation standpoint, the message is clear: marine ingredients have a role to play, not only nutritionally but also in terms of global land-use efficiency. Substitution choices require careful consideration of trade-offs across the whole system.

The Role of Well-Managed Fisheries

One of the strengths of the review is that it recognises the progress made in fisheries management. Many assessed marine stocks have stabilised or rebuilt following reductions in fishing pressure and the adoption of science-based management. Because fisheries draw on existing ecosystems rather than converting habitats for production, sustainably managed marine protein offers an important buffer against the escalating land-use demands of terrestrial agriculture. In biodiversity terms, this is a significant advantage.

A Broader Systems Lens for Policy and Sustainability Discussions

Finally, the authors caution against the increasingly common advice to reduce or eliminate seafood consumption without considering what replaces it. If total protein demand remains unchanged, any reduction in marine protein must be met by terrestrial systems—and the biodiversity costs of that shift are substantial. This is a critical insight for policymakers, NGOs, and anyone shaping sustainability narratives.

The conclusions are direct: efforts to restrict fishing or limit the use of marine ingredients in aquaculture need to account for the wider planetary implications. Without a system-wide perspective, well-intentioned marine conservation measures could inadvertently accelerate biodiversity loss on land, where species are already at far greater risk.

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