In various countries’ fisheries management laws and in international treaties, their formal management goal often refers to the concept of “maximum sustainable yield.” These laws and agreements govern how fisheries are (supposed to be) managed. So I thought it would be good to visit the question of what is maximum sustainable yield or MSY.
“Maximum sustainable yield” is both an idea and, based on that idea, a formally calculated number for how many fish can be caught. The idea of maximum sustainable yield is this: for any wild population, people can extract a certain portion of the population on a consistent basis without harming the population or its productivity, up to some maximum. Past that maximum, the extraction will outpace reproduction and the population will decline.
Why is it possible to take a certain portion without harm? According to the thinking, it’s because populations produce more young than the natural system can support, and because systems vary and populations naturally fluctuate. It is safe to say that humans could kill one tuna a year without harming a tuna population. But could we take one million tuna? Technically, then, the question becomes, “Just how many can we take?” Fisheries science is largely geared to answering that question through the lens of maximum sustainable yield.
Maximum sustainable yield is for fisheries managers an ideal, for ocean policymakers a slogan, for fisheries scientists and conservationists a crude but useful tool, and for some marine ecologists an assumption that has never reflected reality. Its sub-text is that fisheries management can be accomplished without closing any areas to fishing. So it’s also a battleground.
The resulting debate has spawned various ideas, assertions, guesses, and theory about how much fishing pressure the ocean system can support. The answers fisheries scientists have come up with are probably all partly true; but probably none of them are true enough to successfully stabilize the whole global fishing endeavor. It’s a little discomfiting to think that what British fisheries scientist Michael Graham wrote in the 1940s—that “fishery science is strewn with the opinions of those who, while partly right, were wholly wrong”—remains true despite 60 years’ further opportunity to get things mainly right (quoted in Carmel Finlay’s 2011 book, All The Fish in the Sea). Bear that in mind as I continue on with my opinions!
Perhaps the most contentious idea in calculating how much fishing a population can withstand is the idea that heavy fishing is good for the fish. Fisheries scientists believe that a fish population becomes more productive when people take so much that the breeding stock declines by more than half.
Where does that idea come from? The thinking is that fish lay vastly more eggs than can survive, partly because all the fish compete for a limited natural food supply. So, removing many of the competitors leaves more food for the survivors, letting them grow faster. Other people believe it doesn’t really work that way in the ocean.
Some see that idea as arising by analogy to logging, where removing some big trees lets more little trees survive. European foresters, moreover, saw that cutting some old trees encouraged rapid growth of young trees. Rooted in European forestry and advanced in America by Theodore Roosevelt’s Forest Service chief, Gifford Pinchot, was the Utilitarian philosophy of using forests, ‘To provide the greatest good for the greatest number over the longest time.’
That starts to sound like the forerunner of MSY in fisheries, where the goal was first stated along the lines of, ‘providing the most food from the ocean for people, in perpetuity.’ MSY in fisheries is a logical ocean extension of the Utilitarian perspective, rooted in European forestry.
So, fisheries specialists convinced themselves that fishing was good for fish. (Early settlers on America’s high Plains convinced themselves that “rain follows the plow”—but it didn’t.) Espousing “maximum sustainable yield” may sound like a self-serving excuse to take as much as possible. In many cases, it was. But there’s another side to that coin. The idea that there is a sustainable maximum amount that can be caught, and that taking more beyond that maximum can cause harm, is at least an acknowledgment that the ocean has limits.
In Part 3, we’ll look at whether “maximum sustainable yield” has worked.