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An Overhaul for MSY

October 10, 2011

Editor’s Note: I am pleased to introduce a second excellent guest post by Sidney Holt that explores alternatives to using MSY as the central target in fisheries management.  I encourage you to read Sidney’s first post exposing MSY as The Worst Idea in Fisheries Management.   

By Dr. Sidney Holt

Last time I wrote about the features of Maximum Sustainable Yield (MSY) as a goal of fisheries management, calling it ‘the worst management idea yet’ and concluding that it should be put to rest. However, it might be possible to use the idea as a boundary for the highest intensity of exploitation that is acceptable, considering how to deal rationally with uncertainties, how to ensure future profitability, how to avoid excessive impact of fishing on marine ecosystems and how to provide for the wellbeing of future human generations insofar as the use of marine living resources is concerned.

The context of my present interest in this is an exercise in which European nations, the Commission of the European Union and other EU institutions, are now engaged – the revision of the EU Common Fisheries Policy (CFP). The revision will apply to all fishing in the common Exclusive Economic Zone (EEZs) of member states and to operations of all fishing vessels flying any of their flags, both in the common EEZ and on the high seas elsewhere. This exercise is guided by the UN Convention on the Law of the Sea (UNCLOS) that came into effect in 1994 and which is binding on all members of the EU. A key feature of the revision proposed by the EU Commission, now being hotly debated in the European Parliament and by numerous organizations representing fishing industries, producers and marketers of seafoods, and those campaigning regarding environmental concerns, is the adoption of MSY as the prime objective.

First, some background. The basic objectives for the regulated commercial exploitation of marine living resources are specified in Article 61 of UNCLOS concerning areas under national jurisdictions (EEZs) and are as follows:

The coastal State shall determine the allowable catch of the living resources in its EEZ (and take) proper conservation and management measures… to ensure that the maintenance of the living resources in the EEZ is not endangered by over-exploitation. Such measures shall be designed to maintain or restore populations of harvested species at levels which can produce the maximum sustainable yield, as qualified by relevant environmental and economic factors, taking into account fishing patterns (and) the interdependence of stocks… and shall take into consideration the effects on species associated with or dependent upon harvested species with a view to maintaining or restoring populations of such associated or dependent species above levels at which their reproduction may become seriously threatened. [My précis, retaining all relevant wording of UNCLOS]

Regarding the high seas the UNCLOS aims and requirements are practically identical, as expressed in its Article 118:

In determining the allowable catch and establishing other conservation measures for the living resources in the high seas, States shall: (a) take measures which are designed, on the best scientific evidence available to the States concerned, to maintain or restore populations of harvested species at levels which can produce the maximum sustainable yield, as qualified by relevant environmental and economic factors…

UNCLOS Article 62, on Utilization of the living resources, is also relevant to this matter:

The coastal State shall promote the objective of optimum utilization of the living resources in the EEZ without prejudice to article 61. (it) shall determine its capacity to harvest the living resources of the EEZ  Where (it) does not have the capacity to harvest the entire allowable catch, it shall give other States access to the surplus of the allowable catch…

Let us first look at the requirement, noting that it is not optional – if the MSY is not all taken by someone, someone else must be allowed to take the residual ‘surplus’ if they so wish.  This is practically the inverse of the abstention principle so beloved of the US in earlier years. These provisions are all expressed with a presumption that for any given ‘stock’ there is a unique MSY. But that is not so. Aside from all questions of variability and uncertainty there are, for any stock, an infinite number of MSYs.

The highest yield can be obtained by catching all the fish remaining in a cohort – an annual year-class – when that cohort attains its maximum total weight. Call that MSTa, the a standing for ‘absolute’. That there exists such a maximum arises from the fact that in the early stages of life the rate of growth in individual body size exceeds the loss in numbers from natural mortality, but that after a certain age, as growth slows towards an asymptote – a maximum body size – continuing natural mortality overtakes growth and the total weight of the cohort begins to decrease. Eventually there will be just a very few big individuals left until the last one dies.

But it is not practicable to catch all of a cohort in one fell swoop, and even if it was technically possible the cost of doing so, with a huge fishing effort, would be entirely prohibitive.

Now look at another possibility: begin to catch fish from a cohort practically as soon as they are born and continue to do so at all ages. That can lead to there being an MSY – lets call that MSYns, the ns standing for ‘no selectivity’, at some intermediate intensity of fishing generating an intermediate fishing mortality rate. That might be profitable but MSYns is always less than MSYa, probably much less.  Furthermore, while MSYa would have been composed of all big individuals MSYns would be largely young, probably unmarketable fish.

So, consider what trawlers have always done, i.e. to fish with a cod-end mesh that retains all the desirable, marketable fish above a certain age and size, and allows smaller ones to escape, or to fish where there are few or no young ones because they live mainly or entirely at a different depth or in another area. The catches from such an operation would also have a maximum corresponding to an ‘optimum’ fishing intensity. Call that MSYs, the s standing for ‘selective’. But, depending on the mesh size, there are an infinite number of MSYs’s – MSYs1, MSYs2 and so on. These must all be less than MSYa but more than MSYns. The MSYs catches will be composed of a fairly high proportion of fish just above marketable size, and fewer larger, mature individuals. The values-per-ton of these MSYs catches will depend on their composition since fish of different sizes usually fetch different market prices.

The same considerations apply generally to any fishing gear or method that is intrinsically selective – such a hook-and-line or gill net or is deployed in a matter that will have selective results.

All that is said here applies equally to all the cohorts present in a stock during a particular period, such as a year, so we are talking about MSY’s of the stock in the normal sense. Thus for practical purposes the MSY of a stock, and both the size and value of the total catch, depend on with what selectivity of gear, and in which location and season one chooses to operate. If one is going to try to regulate the fishery for sustainable yield, for example by setting TACs or controlling fishing effort, all those factors also have to be specified.

Now let us look at the second phrase of the UNCLOS requirements: “…as qualified by relevant environmental and economic factors…”. This was introduced into the UNCLOS negotiations mainly for two reasons. The first was to deal with the criticism that an MSY might change over time because of environmental changes. Fair enough. The second was to deal with the argument from some states that it might sometimes be desirable, for socio-economic reasons, to fish unsustainably – for example taking, even temporarily, high catches in order to accumulate capital from their sale, perhaps to be used for further expansion of the fishery. The extreme of this attitude is, of course, the ‘mining’ of living resources (often euphemistically and misleadingly referred to as ‘harvesting’) in which the whaling industry indulged throughout the 20th century, and by some fishing industries conducted principally to produce industrial commodities such as fishmeal.

The phrase ‘as qualified by relevant economic factors”, however, is not prescriptive and leaves open a more positive interpretation with regard to direction, whatever might have been the original intention of what was a controversial decision in the UNCLOS negotiations. If the aim is to manage  a fishery only for high sustainable catches but also for value and profit, the phrase opens the way, without departing from UNCLOS principles, to enact regulations that are expected to keep the stock above any chosen MSYs-level, with less effort and hence lower fishing mortality rate than would be needed to catch MSY. So a shift from strict MSYs to a somewhat lower chosen Maximum Economic Yield, (MEYs), for example, would be acceptable within the provisions of UNCLOS. And any MEYs will have proportionately more large fish in it than the corresponding MSYs.

There are, of course, other reasons for aiming at something less than MSY, from a somewhat bigger stock. Dealing with assessment uncertainty is possibly the most important. Computer simulations of management procedures have shown that if unforeseen negative events – such as unintended stock depletion – are to be avoided it is best to regulate for a bigger stock level than a smaller one. Furthermore, recognition that MSY depends as much on the selectivity of exploitation as on the maintained stock level, helps us escape from the unfortunate restrictive focus on MSY ‘levels’ in UNCLOS and other official documents and decisions.

Another good reason is that a lower intensity of fishing than might be needed to yield MSY, or even MEY will, by ensuring a relatively low impact of fishing on the ecosystem in which the target fishes are vital elements, reduce the risk of unintended deleterious consequences of fishing.

Now let’s consider the time-frame of sustainable exploitation of wild living resources. Diamonds may be forever, but sustainability is not. In practice an essential feature of any attempt to devise a management procedure for this purpose has to be the adoption of a finite time-frame for management and, before that, for testing candidate management procedures by computer simulation. The first serious attempt to do this was made by scientists in the International Whaling Commission in devising, in the 1980-90s, a ‘Revised Management Procedure’ (RMP) for the regulation of commercial whaling.

The task set for them was to invent a regulatory regime that would give high long-term catches but with only a very small probability of unintended bad consequences such as unwanted depletion of the stock. If one is trying to balance two or more objectives there can be no single optimum or maximum. The testing of candidate RMPs was done by comparing cumulative catches over a specified management period, which is the same as looking at the average annual catches in that period. The period chosen was 100 years. That satisfied one criterion – that management had to cover at least two or more generations of whales (and, incidentally, humans). But this period was actually set by the limited power of the Cambridge University mainframe computer at that time, nearly two decades ago.  (The calculation time for complex simulations of a time-series increases super-exponentially with the length of time.) The time period is also obviously related to how long we can reasonably expect a management system, and the legal and administrative instruments for implementing it, to endure. Not many people would expect such a social construct to endure for a century. Yet the very essence of something like a science-based RMP is that once one has agreed to implement it the rules must not be fiddled with for political purposes year after year, and the scientific calculations ignored for whatever are this year’s reasons, as has been the EU’s persistent practice)

This matter of the time-frame is not a trivial issue. A few years ago clever Norwegian scientists, working in support of their national whaling industry, came up with a new proposal: as computers were now much more powerful, why not make the management scheme go on for two centuries? Superficially this can seem a step towards true sustainability. But it is not. Making that move would in fact increase greatly the allowable catches in the first few years of the Procedure being applied, which is really all that the industry is interested in.  This happens because it would then be possible to partially deplete the stock with high catches but still have time for it to recover in the second century of management. Very cunning, but spotted in time by other scientists and rejected by them.

There are other features of the IWC’s RMP exercise that would be worth copying in future fisheries management, including the revision of the EU’s Common Fisheries Policy. One of those was to try, in testing new candidate procedures, to ensure that the results do not depend on the properties of a particular mathematical model of fish stock dynamics. And in devising such procedures for managing fishing the choice of multiple aims, and decisions about the priorities among these are crucial. Avoiding unintentional stock depletion while planning for high long-term average catches is one pair of conflicting aims, and dealing with such conflict among multiple objectives necessarily involves deciding priorities among them. There are likely to be other sets, involving – as well as satisfactorily high catches – sustaining a certain level of profit without subsidies (something to which the IWC gave no attention, even though it is likely that sustainable whaling by Northern Hemisphere operators in the Antarctic will nevertheless be unprofitable); a wish to reduce ‘food miles’; a wish to maximize, as far as possible, sustainable production for human food (rather than for feed-stock of other industrial uses, which might call for a different size composition of the catches; a wish to spread fishing throughout the year and to be fair with respect to the interests of various countries and operators of different kinds of vessels and gears; and so on.

Identification of multiple, partially conflicting, objectives of management calls for departure from the institutionalised greed represented by a single MSY objective. So, although MSY – or, even some apparently preferable but simplistic derivative of it such as MEY – might serve as the lighthouse, other beacons will be needed to guide the Revised-EU/CFP vessel safely into port.


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