Comment on Water footprint of marine protein  consumption -- aquacultures link to agriculture

In their article Freshwater savings from marine protein consumption (2014 Environ. Res. Lett. 9 014005), Gephart and her colleagues analyzed how consumption of marine animal protein rather than terrestrial animal protein leads to reduced freshwater allocation. They concluded that future water savings from increased marine fish consumption would be possible. We find the approach interesting and, if they only considered marine capture fisheries, their analysis would be quite straightforward and show savings of freshwater. However, both capture fisheries and aquaculture are considered in the analysis, and the fact that marine aquaculture is assumed to have a zero freshwater usage, makes the analysis incomplete. Feed resources used in marine aquaculture contain agriculture compounds, which results in a freshwater footprint. To correct this shortcoming we complement the approach taken by Gephart and her colleagues by estimating the freshwater footprint (WF) for crops used for feeding marine aquaculture. We show that this is critically important when estimating the true freshwater footprint for marine aquaculture, and that it will be increasingly so in the future. We also further expand on aquacultures dependency on fish resources, as this was only briefly touched upon in the paper. We do so because changes in availability of fish resources will play an important role for feed development and thereby for the future freshwater footprint of marine aquaculture."