Seafood sustainability is such a difficult topic because ultimately it boils down to the idea that we humans have the ability to determine the exact right level of seafood we can take from a complex and not always well understood ocean that will allow seafood populations to not only maintain, but to function more or less as if we were not harvesting seafood.
Wait, does that make sense at all? Is there really some magical line in the ocean that allows us to have our cake and eat it too? What about complex highly interdependent ecosystems? What do we use as a baseline? Do we use historical abundance or recent abundance? How does the harvesting of one species like herring impact the health and abundance of other species that depend on it?
The "truth" if there is one is that sustainability is a "best guess" when it comes to seafood. If you Google "Sustainable Seafood" you'll find a number of species specific seafood buying guides. There is some value to these guides. Most folks that want to do the right thing don't necessarily want to spend their time reading some random blog about seafood sustainability and these guides can be a decent starting point for folks that want to do the right thing.
We think a better way to approach seafood is to have a set of principles.
But, to understand how seafood cards can get things wrong, we have to gain an understanding of how fisheries are determined to be sustainable. Usually this has to do with many sceintific assesments, but the two biggies are TAC (Total Allowable Catch) and MSY (Maximum Sustainable Yield).
TAC is a hard number that defines how much fish fishermen can catch. It is based on fish population assessments and is supposed to be scientifically vetted. MSY is a bit harder to understand, but it is essentially the amount of fish that can consitstently be taken from a population of a single species that will allow the population to maintain over the long term. In simple terms, it is usually around 30% of a "healthy" population of fish.
In some ways they define the same thing, however MSY is more like the speed limit, while the TAC is the actual speed that can get you a ticket. In other words, the numbers are not always the same and are subject to the discretion of the managers.
So, let's get back to sustainable. In effect the TAC defines what fisheries managers think is sustainable. Fishermen have little to no impact on this number. It is defined, determined and vetted by the Science and Statistical Comittee (SSC) of the New England Fisheries Management Council (NEFMC) and accepted or rejected by the NEFMC. So in effect, how much fishermen will catch - whether or not that fishing is sustainable - is determined by managers not fishermen.
So, how can sustainable seafood cards put things like Atlantic Cod on a list of sea foods to avoid when managers, vetted by the best available science, are saying that Cod are no longer overfished? This article is a great exploration of the complexities in particular concerning our local codfish.
So, in sum, managers/regulators are defining sustainable ideally based on science that determines a level of seafood that can be caught indefinitely. As a principle, its a good place to begin to approach sustainability. But if you are like me, you have a healthy skepticism of the ability of scientists and managers to know the ocean well enough to consistently and impartially determine the magical number of fish we can eat without any impact. It just sounds silly to me and reminds me of one of my old friends' skepticism of another magical animal.