We disagree with Jennifer Jacquet and colleagues' criticism that the standard of sustainable seafood certification by the Marine Stewardship Council (MSC) is not sufficiently stringent (Nature 467, 28–29; 2010).

They cite Alaska pollock and Pacific hake as species for which certification has been too generous, given their substantial population declines. But any fish population will fluctuate, including sustainably managed fisheries such as these. The allowable catch can simply be reduced when abundance declines. This strategy enabled successful rebuilding of the New Zealand hoki stock, the certification of which had been challenged by some environmental groups.

The authors argue that the MSC should concentrate on small-scale fisheries. But the largest industrial fisheries should be targeted first — they supply most of the fish for consumption in countries where certification will have an impact. The cost of certification is largely independent of fishery yield, so it is much more cost-effective to certify large fisheries than small ones. We see little evidence that small-scale fisheries are having a lower impact per kilogram of product.

One of the MSC's principles is that “fishing operations should allow for the maintenance of the structure, productivity, function and diversity of the ecosystem”. We doubt that any form of conventional agriculture using a plough would meet that standard. Indeed, retailers who reject some MSC-certified fish still sell crops and meat that have high environmental impacts.