Wednesday, November 22, 2006

The Good Depletion

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.


Anonymous said...

Thanks Mark for bringing this blog entry to my attention. As you surmised, it is of interest to me. I also read your earlier blog on Hilborn's lecture and the discussion that followed. My comments will address them both.

Though I agree with and respect your passionate critique of yield-based fisheries, I recommend you think more critically about the alternative you propose. Taken literally, your proposal to maximize the probability of good reproduction and diversity of life history stages would mean the end to all fishing. This policy would be as undesirable as achieving maximum sustainable yields is unattainable. It contrasts with your specific proposal--to fish stocks in time of plenty and avoid them during hard times. This proposal is slightly more practical but the outcomes will depend substantially on how such things as good times, bad times, fishing hard, and switching are defined. These approaches would also necessitate data streams that better cover pre-recruit stages and have more of a real-time component to them.

Instead of ending all fishing or using a single strategy, what we really need is to spend more time thinking about what we want from fisheries, and using all available data to evaluate potential alternatives for achieving these objectives. Though you focus on Ray's overemphasis on yield, he makes this good point too.

When I have used this alternate approach in fisheries management or marine reserve policy forums, it has generally fostered an open discussion and resulted in a decision that is thoughtful of many objectives, including the long-term ones like conservation and sustainability. It may not be as sexy as fighting for shifting the burden of proof, but it works.

Mark Powell said...


Thanks for your comments. Good point, striving to maximize good reproduction could go too far. How about "emphasize" instead of maximize?

Regarding your point (and Ray's) that we need to focus on defining our objectives: Yes, of course I agree. But I think it would be a shirking of responsibility for scientists (or managers) to say society sets the objectives.

Scientists (and managers) suggest options and predict outcomes, and society chooses based on that sage advice. Scientists (and managers) have a heavy responsibility for what is chosen.

I have friends who were alive (and politically active) when "society" chose to build many fish-killing dams. In particular, I have a detailed history of the Pelton-Round Butte dam complex on the Deschutes River. Leading agency scientists (and managers) promised that we could have dams and fish both, and that techno-fixes like fish ladders or hatcheries could compensate for habitat loss or alteration. Leading fish-smart people argued otherwise and lost. The choice to build those dams was made based on science-based promises that fish would be fine. It was hardly a fair choice.

For fisheries and maximum yield, we still have scientists telling us that we can have our fish and eat them too. Mr. Hilborn isn't backing down from claims that we can have maximum sustainable yield with The Good Depletion (60-80% depletion).

Why wouldn't fishermen and others choose maximum yield? It sounds too good to be true (and, sadly, it is).

I think scientists and managers bear most of the responsibility for "society" choosing maximum yield as a fisheries goal, and enshrining it into law. That's why I think it's the responsibility of scientists and managers to explain the folly of making that choice and sticking with it into the 21st century. We led people into making that choice, we have to lead them out of it.


Anonymous said...

Interesting post, although I believe it's 'Professor' Hilborn :)

Mark Powell said...


In the egaliatarian blogfish world, we want ideas to stand or fall on their own, not based on pedigree ;)


Anonymous said...


Interesting points and well taken. At a seminar I didn't attend, I had a colleague ask Hilborn about the current fishery crisis... The reply that reached me... was that there wasn't one... really surprised me given, the piles of evidence to the contrary.

I was interested in the question (and still am) as to why with all the research and, frankly, very good science, and basically well meaning scientists, and reasonable policy makers and fishers (for the most part).. we are still in a declining fishery situation. This is a real puzzle with no simple answer.

Establishing additional measures other than things like spawning stock biomass will help, as you point out. The difficulty is in measuring things like "ecosystem status" etc. and incorporating thouse into management in a realistic manner.


Mark Powell said...


Thanks for your comments. I also wonder how we can have such problems given the effort applied to solving them. I don't have the answer, and the question drives what I do. Interesting to note that Hilborn and colleagues reviewed the orange roughy fishery in 2006 in Can J Fish Aquat Sci (vol 63) and concluded that management was very close to economically optimal. Others looking at the same (fairly well studied on a global scale) fishery conclude quite the opposite, that it's a crisis. Ugh. Hard to proceed when we don't share a vision on what is success, as Josh said above and Ray Hilborn said in the lecture linked above. Conflicting goals are a major part of it, but it goes far beyond goals IMO.


Anonymous said...

Hi Mark - if we're so egalitarian in the brave new blogworld, why not just call him "Ray"? "Mr Hilborn" comes across as a bit odd in this context :-)

Anyway, I just wanted to say that you provide food for thought. I too was a little worried by what seemed to be an excess of emphasis on "yield" in Ray's lecture, but I found a lot of what he said rang true with my experience in fisheries (and I wasn't originally trained as a fisheries scientist, but in plant ecology, genetics and pathology, so I'm not necessarily interested in "circling the wagons" around the profession).

A coupla quick points before I have to sign off:

1. The graph you use as an illustration is a graph of catch-rate (presumably corrected for various variables) over time, not yeild, nor biomass. This is not a completely specious point - catch rate is not exactly correlated with yield. I've been told that if it was, then its unlikely that you would have been in such big trouble with cod. The signs would have been on the wall a lot earlier.

2. You can't catch any fish at all without causing some degree of depletion. And if you are still catching fish at more or less the same rate over a long period, then I guess that is a fair definition of "sustainability". But in my opinion some of the management systems in use allow fisheries to get too close to the wire - they don't make allowances for uncontrollable peturbations - there is not enough "insurance". And too many of them still don't take into account other ecosystem linkages. And some of the more "high-tech" systems on offer place too much reliance on stock assessment being an exact science - which it is not (although it is not completely invalid, as many people seem to be asserting nowadays and thus throwing the baby out with the bathwater). Etc.

Anyway, keep up the good work of making us think, and keep an open mind yourself. A certain amount of wagon-circling is inevitable in a profession which is under such attack, and where many of the highest-profile criticisms have turned out to be composed of much less supportable science than the mechanisms they are attacking.

Criticism is good. Well-argued defence against criticism is also allowable. Everyone is ultimately stronger for stripping out the bull. But the whole thing falls down when people start using rhetoric instead of logic to make their arguments, and using press-blitzes rather than sustained peer-acceptance to assert their validity.

You don't do it, but a few other people do, and so you might find a bit of unwarranted defensiveness around nowadays...

Piscophile said...

I just watched the video, to the end, and it seems clear to me that while Ray is no fish-hugger, what he is actually saying is that fishery management is successful and legal when it depletes stocks to very low levels (20-40% of virgin biomass).

This is how the density dependent single species model is supposed to work, and under the old MSY definition that is for the most part the law of the land he is right, it’s "not a problem".

Of course to those of us who would like to move forwards with new management that produces more intact and resilient marine ecosystems, MYS is old-school crap. It’s fraught with problems, not the least of which is establishing accurate population parameters, especially natural mortality.

If you listen to the whole lecture, Ray acknowledges that a new paradigm is needed, that society now values ecosystems, and that "Pretty Good Yield" can be reached at 80% of virgin biomass. If one read just your initial post one would conclude that Ray likes overfishing and I can only assume you didn’t watch the whole lecture. He essentially rejects MSY management and concludes by suggesting catches should be reduced to PGY and managed using rights-based systems (even though this will lead to loss of some jobs).

I have also looked critically at successful and failing fishery management systems around the world and concluded the same as far as what works - some sort of rights based access system, whether it is a traditional system as in Papua New Guinea, Maine lobster zone management, or a technocratic ITQ system.

Sometimes in the environmental community we have blinders that delay us from moving forward with sound science and creative solutions. Blinders that lead us to adopt outlandish inference, and dire conclusions that get trumpeted across the land by the popular press accepted as gospel. Blinders that keep us from critical thinking and consideration of alternate hypotheses.

I don't share Ray's pessimism about the value of MPAs, though they certainly are no stand alone panacea.

Marine ecosystems have been profoundly altered by biomass removal, staggering losses of estuarine habitat, and damage to sensitive coastal and offshore habitats by trawls and dredges-- there is a lot of work to do and perhaps not much time. Thanks for keeping this blog and engendering this discussion.

Anonymous said...

I read with interest the discussion re. Dr. Hilborn's position re. "yield-based" fisheries mgt(FM). I must defer to natural scientists such as he on the pop dyn stuff, but here is a comment re. the success failure record. It seems to me that the failures have not been because of the science per se, but because of the incentives as expressed through the political processes of FM. It really doesn't matter whether the target is MSY, O>!F*, gear regulation or whatever if the incentives are all to wheedle the regs around it and/or unenforceable at any acceptable cost to taxpayers. That is where your commenter re. rights based approaches is on target. rights based approaches are not a panacea, but it has been highly successful in some fisheries. Of course, it may well be that those turn out to be the ones for which such approaches are most suited. Time will tell.

Anonymous said...

The first of many problems with MSY is that it refers to the environment as a steady state in which sustainable means sustained forever unless biological conditions change. Nature is anything but a steady state. The variability of the interacting environment is a result of biotic and abiotic factors. This generates variability both in the abundance of resources and in the yields, even if a time-constant harvesting effort is employed. The very concept of sustainable yield relies on deterministic demographic models that cannot be realized nature. Nature itself is not stationary, neither in time or space, therefore the term "sustainable" cannot be applied in fisheries management.
What seems to be continually overlooked, intentionally or not, is that the earth is a finite place, a closed system. If the earth is finite than the relationship between its constituent parts are likewise finite as well as complexly intertwined. Therefore changes in one part of the system produce effects in another part. The term finite has obviously been omitted from the fisheries management dictionary. As a a result it forms the basis as to why MSY has not been achieved in the past and will not be achieved in the future.
Since the birth of MSY, it has dominated fisheries management for decades. Fishery managers make it look good in writing but taken by itself the theory is seriously flawed. No matter which way you calculate the value of MSY, the dwindling numbers of fish populations are speaking loud and clear. Quotas set through MSY are still devastating target stocks. The concept of MSY fails such target species through negative demographic effects especially on large late maturing, long lived species which leaves the smaller fish will lower fecundity. This results in evolutionary changes in harvested species through changes in genetic variance and life history traits. Just as important it does not take into consideration the effects on associated stocks or dependent species. Have fishery managers forgotten that target stocks are part of an ecosystem and harvesting them will impact both species on which they feed and species that feed on them.
Another problem with MSY is it does not solve the by catch issue. Target stocks cannot be taken in isolation and by-catch and incidental mortality of non-target species like other species of fish, invertebrates, marine mammals, birds and turtles can be very high. This is a very serious issue in which the target/by catch ratio can reach levels of 1 pound of target species caught there is 14 pounds of non-target species that are killed and discarded. In a broader issue MSY does not address the impact on the marine ecosystem. It does not alleviate the devastating effects of destructive fishing methods such as cyanide fishing, drift net fishing, dynamite fishing and trawling. These methods have tremendous impacts on the ocean floor, coral reefs and other fragile habitats.
Responsibility for the depletion of fish stocks can be put on government officials in which politics and bureaucrats have continued to encourage overfishing. MSY is calculated from stock assessments which are based on psuedoscience in which uncertainty and insufficient knowledge of the biological characteristics of both target and non-target by-catch species are not understood. Fisheries managers have fought hard against the conclusion that human impact is the cause of the devastated fish stocks instead they put the blame on environmental change. The government's bias has led them not only to ignore evidence of their role in depleting the oceans but to also actively conceal it.
If we want to leave nature as it was then there is absolutely no harvestable surplus production for humans, because harvesting will have the same ramifications through ecosystems. This is the same idea as trophic cascades following increases or decreases of predators in natural systems. Thus the term harvestable surplus is sociological not biological
Although many argue that humans are animals and as such are part of the natural ecosystem, not outsiders and acquiring of resources is a normal activity. The problem with this argument is that as a result of the human population size and technology we are much more than ordinary predators. As a result we are exploiting and causing irreversible damage to everything we can get our greedy hands on.
There is no question now that the world's fisheries have been drastically overharvested. We are depleting lower and lower trophic levels and causing much collateral damage and thereby severely altering marine ecosystems. We need to regulate our own behaviour. Ideally science can tell us what to do but we lack the fundamental demographic knowledge of most populations we exploit and the simple models developed through MSY cannot be applied to maintain the great ideology of "sustainable fish stocks" because populations clearly have more complex and differing dynamics than the world of science will ever be able to completely unveil. Although we continue to apply such ridiculous models as a method of "conservation-oriented" harvesting, this is not achievable because the entire process eventually breaks down when the guiding principles are and always will be money and politics regardless of what science says. Therefore fish populations are dwindling as a result of a double allee effect: Populations are already devastatingly low but we still continue to put unreasonable fishing quotas based on the pseudoscientific calculations of MSY. The pressure doesn't stop there we insist on choking the last breath of life out of fish stocks by placing fat men in ties that call themselves fishery managers who really just view the oceans as a resource to be completely exhausted. It is no secret that money and politics is what drives such an industry not sustainability

Unknown said...
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Anonymous said...

But since most of the fish they are still catching are lower on the food chain and smaller than traditional species, how can fisheries scientists claim there isn't anything wrong? Clearly the change in species caught is an indicator that they cannot argue they worked towards or wanted.