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Maximum Sustainable Yield: The Worst Idea in Fisheries Management

October 3, 2011

Editor’s Note: I am pleased to introduce a guest blog by Dr. Sidney Holt.  Dr. Holt has had a profound impact on fisheries management and ocean conservation.  In 1957, he co-authored On the Dynamics of Exploited Fish Populations with R. J. H. Beverton, a book which was the genesis of the modern age-structured approach to optimal fisheries management. Subsequently, Dr. Holt served as Director of the Fisheries Resources and Operations at the UN FAO, Secretary of the Intergovernmental Oceanographic Commission (IOC), and Director of UNESCO’s Marine Sciences Division.  After 25 years in United Nations organizations, he devoted himself to the conservation and protection of the Great Whales, notably in the IWC.  His contributions have shaped our ocean today.  In recognition of his work, Dr. Holt has received the Gold Medal of the World Wildlife Fund (WWF), the Royal Netherlands Golden Ark, the Global 500 Award of the United Nations Environment Programme (UNEP), and The Blue Planet Award of IFAW.

By Dr. Sidney Holt

Let me begin by explaining my title. MSY both enthrones and institutionalizes greed. It is a perfect example of pseudo-science with little empirical or sound theoretical basis. As a target for management of fisheries, or even as the anchor for so-called ‘reference points’, it is inadequate and its pursuit increases the likely unprofitability, and even collapse, of fisheries.

I have, nevertheless, twice enthusiastically offered my support for MSY. How come? In both cases – regarding the extreme depletion of the populations of large whales, in 1974, and the EU Commission’s recent proposals to adopt it generally in EU waters – the question was how to get away from a policy of seeking merely current sustainability, instead of the recovery of stocks to more productive abundances and states. Shifting from ‘sustainability’ to notional MSY was in those cases an improved, progressive policy. It has, however, its dangers, as we saw with Japan’s pressure, in the 1970s, to reduce hitherto lightly exploited whale populations – such as the minke and Bryde’s whales in the Southern Hemisphere – down to their presumed MSY ‘levels’. I have since thought that maybe one should not support certain things for tactical reasons that one would not support if thinking strategically. My mother sometimes told me that in some ways a white lie was worse than a real one.

The MSY idea first appeared in the scientific literature in 1933 when three Norwegian biologists – Johan Hjort. P. Ottestad and G. Jahn – published a study of the states of the blue and fin whales in the Antarctic and also near Iceland. They hypothesised that if – as many supposed – wild animals increased on an S-shaped curve of  population number against time (they called it ‘the sigmoid’), then the best long-term catches of whales and fishes would be obtained by exploiting them in such a way that their populations were held at the numerical sizes where the curve was steepest – the so-called inflexion point.  The simple mathematical model they used implied that this occurred when the population was about half-way between a very small starting number and the final number that would be reached after a long (theoretically infinite) time – called in mathematics the asymptote and sometimes in biology the ‘carrying capacity’. Hjort, Ottersadf and Jahn called this inflexion catch and the corresponding population number ‘the optimum’.

In the 1930s three ways were known to determine the ages of baleen whales but, although the lengths of all landed whales were measured, available age readings were inadequate for determining the dynamics of the blue whale population; if they had been adequate and the Norwegian authors had used them, the history of fish stock assessments might have been very different because at the time they were well aware of the advantages of studying stocks of fishes such as cod and plaice through looking at the age frequencies in catches. The methods of determining ages of fishes were developed by Norwegian scientists – by counting rings in the scales of  herrings, and in the ear-stones – otoliths – in cod. It is relevant to my argument here that they were able to make their analyses useful because they were able to distinguish at least three age groups of whales in catches: calves and juveniles, immature animals, and sexually mature animals. I’ll return to this later.

The S-curve of population growth used by Hjort, Ottestad and Jahn was derived from the ‘bell’ curve of Gauss (the now-familiar ‘normal’ error function).  They had also considered using an equation posited by a Belgian mathematician named Pierre F. Verhulst but decided that for their purposes practically any sigmoid curve would serve their expository purpose; all the smooth, more or less symmetrical, ones looked similar. Verhulst, a century earlier, was disputing the presumption of the Rev. Thomas Malthus that human and animal populations increase exponentially (that is, like the number series 1, 2, 4, 8, 16, 32 and so on until they run out of food and other necessary resources and then crash, in the human case leading sometimes to revolutions. The vibrant Western European capitalists of the first half of the 19th century didn’t like that; as optimists they preferred Verhulst’s notion of stability to what they saw as Malthus’s pessimistic view of history.

Now Verhulst did not presume that his S-shaped population growth curve, which we generally call the ‘logistic’, had in reality an inflexion at 50% of the maximum population size – he gave it as an illustration of a principle, and it was a simple one because it came from the assumption that the relative rate of growth diminished linearly as the population increased. Anyone who has gone through Calculus-101 knows that a linear assumption is nearly always the easiest one to resolve. This 50% stuck with Hjort, Ottestad and Jahn as if it was a reasonable hypothesis rather than merely an illustration.

In the places where fish population dynamics was being studied as a possible basis for ending or preventing over-fishing –  a term with at least eight usages, some mutually contradictory, but which I use here to mean the tendency for the intensity of fishing to increase until the rate of catch becomes so low that fishing is unprofitable without subsidies – not much attention was given to the Hjort/Ottestad/Jahn paper, although it, and they, were well-known and respected in fisheries research circles. Attention was focused instead on allowing fish time to grow before being caught, and for adequate reproduction; based on a theory linked especially with E. S. Russell and Michael Graham in England, Gunnar Rollefsen in Norway, Oscar Sette in USA and William Ricker in Canada. In fact, a Russian, F. Baranov, had got there already – in 1925 – but the Revolution and the Russian language prevented that from becoming known in Europe and North America until the outbreak of WWII. Their work depended, however, on being able to determine how old a fish was when it was caught. Gunnar Rollefsen, in Bergen, had discovered the latter, very important, method in 1931. By the following year it begun to be used routinely for study of the landings at of cod at Lofoten and Rollefsen applied it to the Northeast Arctic stock of that species. It is remarkable that Hjort, who had been Rollefsen’s mentor, had thought throughout his eventful life that age determinations were a key to understanding fish populations, but he and his successors were much more interested in the annual fluctuations in recruited year classes that the age determinations revealed than in the overall dynamics of the populations they studied. But Hjort understood that those very variations made it extremely difficult to predict future catches well and hence to cure over-fishing by setting annual limits to catches. For him the size of the fleet and how long ships spent at sea were what mattered

At this time – the late 1930s – the work of Michael Graham at Lowestoft, England, on cod and plaice, was the most important, both in theory and in practice. Graham had a sort of mystical attraction to sigmoid curves in nature, which he referred to as ‘ogives’, a feature of Ancient Greek architecture, but instead of following Hjort, Ottestad and Jahn’s lead, he developed a simple age-structured model of a fish population derived from his predecessors, especially E. S. Russell and an American associate, W. F. Thompson, who had long been involved with the North American West Coast halibut fishery and so was very well-aware of the downside of trying to resolve ‘the over-fishing problem’ by regulating fishing effort if one was not also able to limit the fleet size. These ideas blossomed during the war, when Graham was involved in operations research and was associated with a mathematician/engineer, Henry Hulme. Between them, they formulated a simple differential equation which, immediately after the war’s end, became the starting point for the construction and application of age-structured fish population models by Raymond Beverton and me. We remained immersed in the local ‘culture’, thinking always about growth of individual fishes, fishing effort and mortality rates, and the best ages and hence sizes at which to begin to take fish from a recruited year-class (a cohort).

In the 1950s, Milner Schaefer, based in California, was studying first the California sardine (made famous by John Steinbeck’s ‘Cannery Row’) and then the yellowfin tuna of the Central-eastern tropical Pacific. There was at the time no known way to age any of the tunas.  Schaefer grasped Ottestad’s work (it was he, a junior among the three authors of the 1930s, who actually had the S-curve idea and applied it) but tunas, unlike whales, are weighed, not counted, and he plotted the annual catches, by total weight against an index of the abundance of fish in the population. He used for that an index in common use in fisheries research, the catch-per-unit-effort (cpue), effort being measured by such figures as the number and sizes of boats, how long they spent fishing, and so on. Using – actually, mis-using – Verhulst’s equation – which was specifically constructed to deal with numbers of humans or animals – he fitted a symmetrical parabola to his data by a standard but simplistic statistical procedure and concluded that its peak –  by definition at the centre of his graph long the x-axis going from zero to carrying capacity – was ‘maximum sustainable yield’. Schaefer published his first polished paper on this in 1954 and the slope of his logistic curve fitted to tuna population size was proposed as the MSY of this stock for management purposes.

In the early 1950s the United States was negotiating a peace treaty with Japan and at the same time deeply interested in the evolution of the international law of the sea. This unexpectedly set the scene for adoption of Schaefer’s hypothetical and untested model by fisheries managers in the US and, eventually, far and wide. President Truman had laid claim to sea-bed resources far out to sea on the continental shelf and some Latin American states responded to this by declaring their jurisdictions over swathes of ocean up to 200 nautical miles wide.

Japan, always dependent on the sea for food, had been encouraged by General MacArthur, commander of the occupying forces of the defeated and practically starving country, to resume whaling in the Antarctic as soon as the war ended. The US was, however, determined to prevent Japanese fishermen going to the Eastern North Pacific  to catch salmon at sea rather than as they ascended North American rivers. The salmon fisheries were at that time by far the most valuable of American fisheries although they were later overtaken by the Pacific tuna fisheries. So how would the Americans keep the Japanese out of those fisheries?

The American-side negotiators of both the peace treaty and. simultaneously. of a trilateral convention for the management of North Pacific fisheries generally (the USSR being carefully excluded from the quartet of interested countries) came up with what they thought was a great idea. They called it the Abstention Principle. The new principle was that if a coastal state was already fully utilising the fish stocks off its shores other states would refrain – abstain – from engaging in that fishery. The next question was “What does ‘full utilisation’ mean?” America’s answer: “Taking MSY”.

In the 1960s the United Nations became much involved in updating the law of the sea, which was still about where Hugo Grotius, a famous jurist in the Dutch Republic, had put it at the beginning of the 17th century, apart from relatively minor changes resulting from the rise of British sea power and bigger guns on ships. The UN had asked its International Law Commission (ILC) to ‘codify’ the law for modern times, someone had heard about ‘optimum fishing’, and the ILC put the words ‘conservation’ and ‘optimum’ in its report, I think the lawyers got the idea from the Preamble of the International Convention for the Regulation of Whaling, signed in 1946, which was written by an American biologist cum diplomat, Remington Kellogg, who led the US delegation to the 1946 conference. The ILC report was the basic document of a big UN Technical Conference held in Rome in 1955, hosted by the Food and Agriculture Organisation of the UN, for which I had gone to work two years before. I found myself recruited to the secretariat of that conference and also writing a basic working paper for it, with my two bosses – Geoffrey Kesteven from Australia and Donald Finn, a Canadian who was at the time Director of FAO’s Fisheries Division. In fact FAO only had a Fisheries Division because Finn had fought for it, as a member of the Canadian delegation at the conference in Quebec in 1945 that founded the FAO.

FAO staff and most of the participating UN member nations – especially the USSR and UK – were not at all enthusiastic about the US insistence on writing both the ‘abstention principle’ and MSY into the envisaged new draft convention on fisheries. In fact my friend Mary Carmel Finley, a historian from Oregon, recently dug up now available secret cables between the US Embassy in Rome and Washington DC saying what a nuisance we – Kesteven and me but mostly me – were being to the US policy objectives (Her book about all this has just been published, so I don’t have to rely on my fading memory of those long-gone days: All the Fish in the Sea: Maximum Sustainable Yield and the Failure of Fisheries Management).

The 1955 Rome conference was the scene of a gentlemanly confrontation between Graham – who chaired and addressed the opening session – and Schaefer, who was one of the invited speakers. In his address, published the following year by the UN under the title ‘Concepts of Conservation’, Graham wrote:

“In the Old World [authorities] have not as yet made any explicit choice among the possible qualities of the fishery – annual yield, catch-per-unit-effort, average size of fish – but in the New World the choice of maximum yield has been explicit in all recent international conventions”, that is, not including the Permanent Commission set up in 1953 based on the 1946 (London) Convention for the Regulation of the Meshes of Fishing Nets and the Size limits of Fish’. The negotiating conference of 1946 had tried to reach agreement among all the participating European nations to limit the tonnages of fishing fleets to pre-war sizes, but failed in this, as also in reaching agreement on the principle of setting limits to catches.**

Although no other countries would, in 1955, wear the ‘abstention’ gimmick, the particular version of MSY theory got into the subsequent diplomatic negotiations in Geneva in 1958.  The five new conventions signed there had rather limited effect on fisheries or anything else in the following decades, mainly because there was no agreement on the width of the territorial Sea, and without that no one knew what ‘the high seas’ meant. The problem was not resolved until the new comprehensive Convention on the Law of the Sea was signed, after a decade of negotiation, in 1982, and even that did not come into effect until 1994, and the US Congress has still not ratified it.

Through this long period of uncertainty the idea of conservative management by trying to hold exploited populations at a certain optimum ‘level’ to provide MSY has become solidified in laws and regulations, with no more science than there ever was to support it.  In 1977 Peter Larkin, at the University of British Columbia, prematurely and perhaps unwisely published what has become a famous paper in our field, entitled “An Epitaph for MSY.” But MSY is not yet dead, though it could be moribund. It could be, for example, that an MSY would be obtained from ‘stocks’ held at more or less than 50% of their presumed ‘carrying capacity’, but no one has determined that empirically and convincingly for any fish (or whale) population. But there are more fundamental causes for suspicions about it, and resentment of its presumption. My favorite is that the assumption that the biological productivity of the population, and hence the rate of sustainable yield that might be taken from it, is determined solely by its size or density. But this is manifestly not so. Two populations of the same species, of exactly the same biomass, and with the same growth rates but with different mortality rates due to both or either fishing and natural causes can have vastly different productivities and hence sustainable yields. The sustainable catch in weight and value depends as much on the age and so the size composition of the population as it does on its biomass. So the harping on desirable ‘levels’ of stock, in laws and regulations, and so on, in advice to be offered by scientists to administrations, is thoroughly misleading and only, at most, half the story. How old are the animals in the catches and for how long and far they have been allowed to grow is as important as their numbers or even their combined weights. Furthermore any MSY calculation depends critically on the pattern of selectivity of fishing – that is, on what ranges of fish size and age are being exploited.

The history of the regulation of whaling provides a perfect example of this anomaly. The whaling industry has always been interested in size because that determines commodity production and hence potential profitability, and that applies across similar species (such as the baleen whales) and within species. But for regulation, whalers mostly wanted to deal in numbers. The average lengths of every species of baleen whale being killed in the Antarctic declined throughout the intensive whaling of the 1930-70s. This was noted every year by the Bureau of International Whaling Statistics (BIWS) in Sandefjord, Norway – the home of the Norwegian Antarctic whaling industry, a city built from the carcasses of blue whales – and by the scientists working in the International Whaling Commission(IWC). They knew this when they devised the IWC’s New Management Procedure – the move from sustainability to MSY as a policy objective – in 1974-75. They agreed to present the case for regulating the catching of each species separately but said that the numbers game should soon be replaced by efforts to maximise the total weight of catches. Few realized just how big had been the reduction in sizes of caught whales in terms of weight, because – unlike with fish – it’s hard to weigh a whale. But we know that the weight of a whale is roughly proportional to the cube of its length, but also that account has to be taken of the enormous change in a whale’s weight in the time from when it arrives in polar waters to feed and when it migrates to warmer waters to breed. The average weights of the largest species, the blue and fin whales. in catches declined by 25-30% during the first decades of Antarctic whaling – a substantial economic factor, especially when combined with the declining numbers. The IWC itself agreed in principle, in 1974 to move to an MSY by weight target, but would not implement it at once, and then forgot about it. The scientists also forgot about it and when they had a second chance, in the 1980s, to invent a Revised Management Procedure, they accepted without question the insistence of the whalers not only to retain the numbers criterion but also to target the maximistaion of those numbers instead of the more rational maximization of long-term profit – the difference between the market value of the catch and the cost of taking it. The latter calls for a lower rate of exploitation (what scientists call fishing mortality rate) resulting eventually in somewhat larger stocks, but taking longer to recover to those ‘levels’ and corresponding population structure by ages and sizes. And of course whalers, like fishermen, would not want to have to wait longer than absolutely necessary before resuming or cranking up their operations.

Recently, in a global review of the states of fish stocks, consultants to the World Bank and FAO have demonstrated that the MSY approach has led to hugely unprofitable fisheries needing heavy subsidies for continuation, and that accepting a slightly lower total catch figure, obtainable with a much reduced fishing effort, global fisheries could be highly profitable again. That is possible because of the usually rather flat-topped shape of curves of sustainable yield against fishing mortality rate, hence fishing effort. Another important feature of these exercises in writing management rules is that – especially for whaling – no attention is ever given to the question of whether high cost operations in, say, the Antarctic, would be profitable if catch limits are kept at MSY levels (after depleted stocks have been allowed to rebuild, that is), especially relatively low ‘precautionary’ ones.

This sort of feature has been known by professionals for a long time. Ray Beverton and I explained it in the book we wrote together on the Theory of Fishing in the late 1940s (published 1957) and in that period the same was argued by other economists and fisheries scientists. However, the main point I want to make here, in support of my provocative title, is another one. It concerns the consequences of the wide acceptance of the kind of theory of fishing first put forward by Milner Schaefer and promoted vigorously and politically by successive US fishery administrations. It is called, in the scientific literature, the surplus production model. I love that phrase. It always reminds me of Karl Marx’s surplus value, his theory based on the fact that workers in industrial societies produce more than they can themselves consume (the ‘surplus’ being, of course, taken over by the factory or land-owners). So fishes and whales reproduce and grow more than they need to for their own comfort, thus kindly providing a potentially sustainable yield for us. Karl was a mathematician too and was not impressed with academic efforts to demonstrate that ‘sustainable development’ as we now call it – is stable and close to Paradise. Victorian entrepreneurs preferred mining, as do whalers – it’s much more profitable in the short-term, which is what mostly matters to them. Professor Daniel Pauly recently described surplus production as “an emergent property” of an evolving ecosystem, I prefer to think of it as another common property of complex systems: a tendency to revert to chaos when pushed.

So, what surplus production theory does is focus regulatory attention entirely on the desired outputs and consequences of the regulatory process – future, usually next year’s, catch – and the desired biomass of the exploited population. This remains so even when some attention is given to the composition of the catches, mainly by sizes of individuals and sometimes also by sex. Hence almost total concentration is placed on Total Allowable Catches (TACs), what the IWC calls ‘catch limits’, what others sometimes call ‘quotas’ (In IWC-speak  ‘quotas’ means something quite different: agreed national or other splintered allocations of parts of an overall catch limit). And, since fish populations are notoriously variable – especially but not only as a result of the variability of the annual recruitment to them of young fish, the setting of TACs looks rather like trying to predict the unpredictable, which leads – apart from anything else – to annual or short-period advisory numbers going up and down like YoYos – something else the industry doesn’t like much.

Efforts are often made to limit the number of too-young fish caught be setting minimum lengths of fish that may be retained or marketed.  Because of the large variability and uncertainty in fishing this means that fishermen can practically never avoid illegally catching small fish (or whales). Then, as the stock declines because of intense exploitation the proportion of young (small) fish in the population declines as does that in the catches and, inevitably the unintended catches of under-sized fishes increases. The combination of regulating total catches and setting minimum legal sizes of fish has led to a huge global problem wherever fishing is regulated – that vast quantities of dead fish are dumped. In some fisheries the discards now even outweigh the legal catches! Discards have been increasing partly because the proportion of young fishes in the population is higher, and partly because species TACS in, particularly, multi-species fisheries must always mean that fish are thrown away when that species limit has been reached but other species remain open for capture.

Let me interject something here. There is a widespread illusion that the increasing proportion of smaller fishes of a species, is due to the selective catching by fishermen of the biggest fish available. In some fisheries there is certainly an element of such deliberate selectivity but generally the scarcity of older, larger fish comes about as an inevitable combined effect of unselective fishing (all recruited fish being more or less equally liable to capture), high total mortality rates and the annual influx of large numbers of small recruits.

To summarise: the fundamental management error is to try to control a complex and largely unpredictable system by controlling its output and consequences rather than the inputs. Those, in the case of fishing, are mainly and usually the fishing effort, which determines the fishing mortality rate induced, and the gears and operational modes that determine which fishes in a population of fishes of different ages and sizes are most liable to be captured; that is, for example, by regulating mesh and hook sizes, locations and seasons and times of fishing, and so on.

In the first years after WWII the Western European fishing nations, negotiating among themselves the management of fishing mainly in the North Sea and elsewhere in the NE Atlantic, were looking to limit fleet sizes (and possibly the sizes and engine powers of vessels) as well as the mesh sizes of the cod-ends of trawls. Talking about TACs came much later, after the push for MSY from the US was well underway.

The US and Canada had had a bad experience with limitation of fishing effort in the 1930s, especially in regulating the West Coast halibut fishery. Limits were set bilaterally to the number of days the boats could stay at sea fishing halibut. Eventually the open season was down to just a few days. Of course the halibut Commission should have limited the number of boats licensed to catch halibut but it was not authorized to do so. This was because the US authorities argued that it would violate their Constitution to limit the right of anyone and everyone to go fishing. That impediment to rational management persisted into the fisheries negotiations for most of the post-war period, during which the TAC approach became deeply embedded. Naturally, success could come only from limiting fishing power – that is an index of the fishing mortality rate that a fully utilized fleet could cause, not simply by limiting how much of its power the fleet was permitted to exert, such as by setting short open seasons for fishing.

In this century we have seen in some places limitations being set for fishing power of fleets and/or vessels. This has to do mainly with dealing with a general over-capacity, renovation of old vessels or their removal from the fleets, and the reduction of subsidies. But in no case of which I am aware has a serious effort been made to install a rational fleet power and effort control for the purpose of bringing stocks to optimal or other desired states.

Looking forward, I think there are two factors at present in the states of many fisheries that are ready to play a crucial part in changing how we view the alternatives of regulating outputs vs inputs. One is the now recognized negative consequences of waste by a huge volume of discards, a problem that I think cannot be fully resolved under a TAC regime although it can probably be ameliorated by complicating the rules even more than they now are. The other is the general reaction against subsidies that encourage continuation or even expansions of fishing power and potential fishing effort in situations where fishing should be contracted if future sustainability –  maximal or not – is desired.

I have no doubt that it is going to be difficult to drag MSY from the legal, conceptual and pseudo-scientific cubby-holes it now occupies, and bury it properly in hallowed ground as Peter Larkin no doubt hoped. This should be done with reverence. Two fisheries scientists – Andre Punt and Anthony Smith – published a chapter in a book a few years ago describing MSY as a ‘Gospel’ and recounted its ‘birth, crucifixion and reincarnation’.  In a future post on this blog, I’ll explain what I understand by ‘reincarnation’ here. I think MSY lived its long, somewhat disreputable life – nearly a centenarian, though sometimes it served a good and useful purpose. It should now be left to Rest In Peace, but visited from time to time.

** There is interesting information about this in the documented discussions within the UK in preparation for the 1946 London Conference that created the Permanent Commission. Several options were considered: designate areas closed to fishing, set catch limits, control trawl mesh size, set minimum landing size by species, and limit the sizes of fleets to no more than pre-war sizes. The British gave priority to this last, partly because they had thoughtfully built many wooden mine-sweepers during the war expressly designed to serve as near water trawlers after it. Other European nations had lost much of their fleet or had already made plans for great and rapid expansions.  Apart from achieving sustainable and profitable fishing, two other factors were important in those discussions: the desire of the Navy to have available adequate numbers of private vessels for service in time of (the next) war – as well as auciliary seamen – and the social need to provide employment and keep fishing communities alive.

12 Comments leave one →
  1. Magnar Aksland permalink
    October 7, 2011 3:40 pm

    I total agree that MSY is a bad idea for management of fish.
    But “Catch per unit Effort” is also a bad method in assessment of fish. I call it “The tragedy of assessment” method. I have derived several paradoxes from the assumptions behind the CPUE method (not published), that do not contain the area, although all fishery goes on in the area.

    Best regards

    Magnar Aksland
    Department of Biology
    University of Bergen

    • October 10, 2011 12:09 pm

      Thanks, Magnar. That’s a really important point. Would you perhaps have any interest in writing a post on these paradoxes? It seems these would be good to share with the fishery management community.

  2. Amy permalink
    March 7, 2012 9:02 am

    No harm in asking – Is there anyway of contacting Dr Sidney Holt regarding the issue of MSY? I’m writing an article on the EU Common Fisheries Reform and the proposal to turn towards a maximum sustainable yield management approach, and would love comment from him – although I can imagine he would be quite a busy man.


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