Fish depletion is not a problem, it's the goal of fishery management. So says Ray Hilborn in "Re-interpreting the Fisheries crisis." So don't worry about disappearing fish, it's part of the grand management plan.
Thus we have The Good Depletion; it allows us to maximize our fish catches. Or so say the equations. The Good Depletion has us liquidating the big fish, shrinking population size by 60-80%, and thus increasing the "productivity" of exploited fish populations. Mr. Hilborn says the decline shown in the figure is not a problem, because we're still catching plenty of fish.
The Good Depletion was an advance in the mid 1900's, and it has some practical value. But it's time to give it a gold watch, a rocking chair, and a graceful retirement. Unfortunately, Mr. Hilborn and others want to keep it working in it's dotage.
We need a new paradigm for 21st century fisheries, and here's what I think it needs. It should maximize the probability of good reproduction years by valuing big fish (because of high reproductive value) and life history diversity (e.g. wide range of spawning times and places). It should maintain fish populations' geographic and age distribution. In brief, it should emphasize the value of what's in the ocean, not what comes out. Fishing should "make hay when the sun shines" by fishing hard during fish population booms, and switching to other species during lean times when reproduction is weak. To me this would be good ecosystem-based fishery management.
This whole fight reminds me of the transition in managing public old-growth forests of the Pacific northwest. When I came of age, we were clearcutting old-growth forests to produce maximum sustained yield, following the rationale of The Good Depletion (forestry version). It failed for many reasons, such as the forests that didn't regrow well in hot southern Oregon, or the wildlife that went missing in massive tree farms.
Science has undermined the assumptions of The Good Depletion (fisheries version). Equilibrium doesn't exist, all spawners are not equal, life history diversity is important, the ecosystem context matters, etc., etc.
Interestingly, Mr. Hilborn says this within the family, just not in public when The Good Depletion is threatened by outsiders. According to Mr. Hilborn and colleagues: "For some years the concept of maximum sustained yield (MSY) guided efforts at fisheries management. There is now widespread agreement that this concept was unfortunate," and "Distrust claims of sustainability. Because past resource exploitation has seldom been sustainable, any new plan that involves claims of sustainability should be suspect."
Circling the wagons around The Good Depletion won't save it. I suppose the testiness of its defenders (watch the video link) is evidence of the coming paradigm shift. Fishery scientists would do well to help fisheries make the transition, rather than propping up The Good Depletion until it's really too late and everything falls with a great crash.