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The dark side of farmed salmon: their diet threatens marine species

Impact of aquaculture (farmed salmon) on biodiversity.

The rapid decline of biodiversity has become a major concern in recent years. Human food is the main cause. If terrestrial biodiversity is the subject of many studies, marine biodiversity is less often studied. This is the subject of this case study.

While the share of fish in the human diet is increasing, what is the impact on ecosystems of the various methods of producing seafood products? Current marine stocks are not sufficient to cover global demand, and in recent decades, aquaculture has become increasingly important.   Our study focuses on the case of salmon (Salmo salar), one of the most consumed fish in the world, to determine its impact on marine ecosystems through two production methods: fishing andaquaculture.


Goal: combine LCA and ecology


The goal of this study is to investigate the impact of aquaculture on biodiversity. The method used is Life Cycle Assessment (LCA) applied to the production of aquaculture salmon until its arrival in port (Figure 1). In a second step, this study will compare the results obtained by aquaculture with those of fisheries, which are highly regulated in Norway. Throughout the study, we consider the impacts of one kilo of fresh salmon upon arrival in port.


Figure 1: System boundaries of the case study

The LCA indicators cover three of the five pressures on biodiversity: habitat change, pollution and climate change. In this study, we also cover the two missing pressures: overexploitation and invasive species. We rely on the ecological literature for this.



Figure 2: A) : Impact split between farmed salmon diet and other elements considered in the modeling such as diesel, electricity… B) Relative impact in % of farmed salmon (orange) compared to harvested salmon (green). The LCA method used is ReCiPe 2016 (H) endpoint for ecosystem quality.

Figure 2A highlights the dominant influence of salmon diet in the impact of farmed salmon. Figure 2B shows how the biodiversity footprint of farmed salmon differs from wild salmon.

Furthermore, it should be noted that the impact of fish diet is not limited to the impacts usually considered in LCA: land use, climate change and pollution. Indeed, the diet of farmed salmon is made up in particular of fishmeal, essentially from Peruvian anchovies. As we can see in figure 3, these stocks are currently overfished whereas the impact on wild salmon is controlled due to strict regulations and fishing quotas. Thus, if aquaculture has made it possible to preserve wild salmon stocks, it is important to note that the problem of overfishing has been displaced and not solved, since Peruvian anchovies will disappear within 10 years if we do not react (Figure 3).

Figure 3: Projected evolution of wild salmon and Peruvian anchovy stocks for the next 30 years. The y-axis represents LPY (Lost Potential Yield) which illustrates the vulnerability of the stocks as described by Emanuelsson et al. (2014) while the x-axis illustrates the date at which the loss of yield (LPY) is potentially reached. Negative values of LPY are synonymous with stock regeneration and thus sustainable fisheries management.

In addition, it is important to know that some farmed salmon can escape from the cages in which they are raised. They are therefore considered as « potentially invasive species » because of their strong propensity to spread parasites (sea lice) to wild species. Furthermore, when escaped salmon breed with wild species, their offspring are often less fertile, which gradually leads to the disappearance of the wild species. The impact of farmed salmon as an « invasive species » can be seen in Figure 4. Note that wild salmon have no impact as an invasive species since they are native to the area.

Figure 4: Invasive species impacts between farmed and wild salmon.

Conclusion :

This study shows that farmed salmon production has a significant impact on ecosystems.  It should be noted, however, that the low impact of wild salmon is mainly due to the recent introduction of strict regulations concerning wild salmon fishing in Norway, which now makes it possible to preserve the species.

 On the other hand, there is an urgent need to find sustainable diets for farmed salmon that meet their nutritional requirements. A promising avenue is to develop a diet based on insect meal. Finally, the scientific literature highlights the potential impact of farmed species to cause significant damage to ecosystems when they manage to escape. Our study shows a moderate impact of escaped salmon, consistent with the relatively non-invasive status of escaped salmon compared to other marine invaders.

This study allowed the PBF (Product Biodiversity Footprint) method to be applied for the first time to seafood products. The method has been specifically adapted to meet the needs of the sector, namely: i) taking into account overfishing and ii) quantifying the impacts of invasive species in the marine environment.

It should also be noted that this project was carried out in collaboration with a team of students from the Ecole Polytechnique. Thanks to them for their work and their unfailing motivation which allowed the realization of this work. It was published by European Buisness @ Biodiversity and can be found here.

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