The idea that fisheries have a “maximum sustainable yield” was first articulated in the mid-20th Century. (For a history, see Carmel Finlay’s book All The Fish in the Sea; Maximum Sustainable Yield and the Failure of Fisheries Management. And for a contrary view on how much of the failure should be blamed on the concept itself, see my review of the book in Science magazine.)
Opinions on the formalized concept of “maximum sustainable yield” in fisheries seem to fall into several camps: 1) those believing the concept is sound, 2) those believing the concept is fundamentally flawed, 3) those believing it could work but has seldom really been implemented.
The concept of maximum sustainable yield has obvious weaknesses. One, the basis is that the ocean (like the rest of living nature) creates “surplus production,” meaning more juveniles than could possibly survive to adulthood. (Early proponents of MSY in the 1940s thought fish left in the ocean were “wasted” because they “just die.”) But there really is no surplus; what fisheries scientists call “excess production,” the rest of the ocean considers “food.”
That leads to problem two: the thinking on MSY wholly ignores food webs. If herring, say, can realistically produce a maximum sustainable catch for humans according to MSY calculations, where does that leave things that eat herring, such as tunas, whose own MSY can’t be realized if we’ve already eaten much of their food. Even though it’s so basic, MSY doesn’t account for this.
Three, MSY is focused on taking the maximum. Focusing more on the word “maximum” than on “sustainable” has proven a risky strategy because it leaves no margin of error.
Four, because fisheries scientists have assumed that there’s only enough “room” in the sea for a limited number of eggs to survive to adulthood, they’ve been comfortable with the idea that a limited number of eggs is just fine. Most fisheries scientists don’t consider a population “overfished” until it’s only about one-third what it was before fishing. In other words, they consider fishing down a population until it’s two-thirds depleted to be their “target,” since they believe that fishing increases the productivity of the fish. Consequently, they consider a deeply depleted population to be “fully recovered” when it’s really only one-third as abundant as it would be without fishing.
And they don’t value very large, old fish in the ocean, because they think it’s best if a fish is caught after it finishes its period of rapid growth in the prime of its life. Fish scientists, on the other hand (whose profession is the actual biology of fish, as opposed to fisheries scientists, whose profession is more about fishing), have in the last couple of decades shown that the biggest, oldest fish lay vastly more eggs and so are vastly more valuable as breeders. They also lay eggs that are larger, better supplied with nutrients, and therefore better poised for survival.
And finally for now, marine ecologists have shown that it’s important for a population to be able to produce vastly more eggs than can survive in most years, because population abundance tends to be maintained by high survival in unusually favorable years. Since unusually favorable years are unpredictable and widely scattered, the population must be poised to take advantage of them when they occur. But that’s less possible if the population is depleted, and dominated by younger breeders.
Then there are practical problems: Once you allow a population to be depleted by two-thirds because that’s your “target,” what do you tell the boats that were doing all that fishing? This is one of the main reasons this system hasn’t worked politically. On the scientific side, how should we account for natural fluctuations in population numbers, since fluctuations mean that the MSY would have to vary? Doesn’t that imply that there is not really one sustainable yield? What is the MSY where different breeding populations—some very abundant, and some small—mix on the fishing grounds? In that case, how do we protect the weak stocks? (There are plenty of cases like that.) And what if the fishery catches different species in the same net? And what if some of those species are slow-growing and others fast? Can MSY-based management really cope with those common situations? Further, doing the calculations requires a lot of good data and good information about the fishing fleets. And applying the MSY-based numbers as real-world catch limits requires good management, monitoring, and enforcement systems. In much of the world, these conditions simply don’t exist.
Even where the data are good enough, fishing industry pressure and the resulting lack of political will often causes fisheries managers to simply ignore scientists’ advice. Then managers allow fishing far in excess of MSY, resulting in fish depletion.
Those might all add up to reasons enough to discard the concept. Yet, where it has been applied, MSY seems useful despite its flaws. That’s probably because in a world of too many people and too much fishing pressure, any limits are better than no limits. Ever since the U.S. extended its territorial claims to 200 miles from the coast in 1976, Alaska’s fisheries managers generally held catch limits to the MSY levels recommended by scientists. New England’s managers often ignored scientists’ recommendations and warnings. Alaska’s fisheries remained healthy and profitable, but New Englands’ crashed and burned. For some other fish populations, holding the catch to MSY-based levels is helping arrest declines and facilitate recovering trends.
Ending overfishing—by holding catches to the MSY, and allowing breeding populations to recover to levels capable of generating the maximum sustainable catch—is now mandated by U.S. federal law. I think this can help a lot. But I don’t think it can solve all our problems. Or work worldwide.
The effectiveness of all fisheries management depends on enforcement. This ranges from governmental systems to peer pressure. But enforceability depends on people understanding the rules, and a general willingness to comply. Most of the world lacks these conditions. Most of the world has also demonstrated an inability to form consensus, especially across national borders.
I am often asked where in the world there is now “effective fisheries management.” If that means sustainable fishing, sensible rules, effective enforcement, recovery trends for depleted species, and a modicum of protection for non-target animals such as seabirds and turtles (where turtles are not targeted), my reply is: The United States, Canada, Australia, New Zealand, the Falkland Islands and South Georgia. That’s about it. And even those places have problems. Europe, where effective management would require international discipline, suffers a chronic lack of such discipline in fisheries. Africa, South America, most of Asia, and the Antarctic suffer either from poor frameworks, poor enforcement, corruption, and illegal fishing. Africa is a particularly tragic case; much of the overfishing that harms Africans is done by European boats whose owners pay underpriced fees in exchange for fishing access.
Nowadays, we seem to understand that the concept of maximum sustainable yield has limited usefulness. Seeking a truly sustainable future for fisheries, many scientists and conservationists are turning to creating networks of marine reserves which can conserve natural processes, let fish recover, and serve as breeding grounds and “factories” for fish that will leave the reserve and support fishing. Others are trying to develop a science and practice of “ecosystem-based management” that can succeed in maintaining everything from food webs to fisheries to evolution.
These ideas have a long way to go. But fisheries management has not generally succeeded, so new ideas are needed. Whether any idea can really work long-term without arresting human population growth is another question.