Maximum Sustainable Yield (MSY): Are we MSY-ing something?


A story by Mike Urch, (MSY not ideal solution for fisheries management) in SeafoodSource on 29 March, 2013 got my attention.

Simply, BMSY is the target reference point for most global fisheries.

It certainly is the case in New Zealand, where the Fisheries Act 1996 (s 13(2))  provides for the setting of total allowable catches that—

(a) maintains the stock at or above a level that can produce the maximum sustainable yield, having regard to the interdependence of stocks; or (b) enables the level of any stock whose current level is below that which can produce the maximum sustainable yield to be altered—

(i) in a way and at a rate that will result in the stock being restored to or above a level that can produce the maximum sustainable yield, having regard to the interdependence of stocks; and

(ii) within a period appropriate to the stock, having regard to the biological characteristics of the stock and any environmental conditions affecting the stock; or

(c) enables the level of any stock whose current level is above that which can produce the maximum sustainable yield to be altered in a way and at a rate that will result in the stock moving towards or above a level that can produce the maximum sustainable yield, having regard to the interdependence of stocks.

So what is a Maximum Sustainable Yield?

MSY is extensively used for fisheries management. Unlike the logistic (Schaefer) model,MSY has been refined in most modern fisheries models and occurs at around 30% of the unexploited population size. This fraction differs among populations depending on the life history of the species and the age-specific selectivity of the fishing method.

The official New Zealand Government definition of MSY is:

“For the purposes of the Harvest Strategy Standard, maximum sustainable yield is the largest long-term average catch or yield that can be taken from a stock under prevailing ecological and environmental conditions. It is the maximum use that a renewable resource can sustain without impairing its renewability through natural growth and reproduction. For most quota management stocks, the total allowable catch is set at a level that either moves the stock towards, or maintains the stock at or above a biomass level that can support the maximum sustainable yield (section 13 of the Fisheries Act 1996).”

Figure 1

The key assumption behind all sustainable harvesting models such as MSY is that populations of organisms grow and replace themselves – that is, they are renewable resources. Additionally it is assumed that because the growth rates, survival rates, and reproductive rates increase when harvesting reduces population density, they produce a surplus of biomass that can be harvested. Otherwise, sustainable harvest would not be possible. Another assumption of renewable resource harvesting is that populations of organisms do not continue to grow indefinitely; they reach an equilibrium population size, which occurs when the number of individuals matches the resources available to the population (i.e., assume classic logistic growth). At this equilibrium population size, called the carrying capacity, the population remains at a stable size  (Image: Wikipedia)

Figure 3

Maximum sustainable yield occurs not at the maximum population level, but rather at a lower, optimal population level. “The highest possible rate of use that the system can match with its own rate of replacement or maintenance.” (Source: Dolores Gende. Environmental Science) (Image: Wikipedia)

The concept of Maximum Sustainable Yield (MSY) for managing fisheries gained popularity in the 1930s (a slide below suggests the theory was postulated in 1935). It then increased in popularity in the 1950s with the introduction of “surplus-production models.” As an apparently simple and logical management goal, MSY was adopted as the primary fisheries management goal by several international organizations and countries. Apparently the USA adopted it in 1949 interestingly enough as a way of management objective for stopping Japanese fishing vessels coming into its waters to catch salmon. The 1960s and 1970s, saw some researchers challenge the capability of MSY in dealing with real world complexities such as food chain interactions, changing ocean environments, and so on. However no real challenge to the management paradigm has really gained any traction (until recently).

Graham’s Theory ofSustainable Fishing (1935):

Graham’s Theory ofSustainable Fishing (1935)
Click picture to see UNEPSCS presentation

Very basically MSY works like this:

  • At low population size the rate of population growth will increase because the environmental resistance factors are low.
  • At low population size, the rate of population growth will increase until environmental resistance factors begin to limit population size. This point is MSY.
  • As the population size becomes larger than the MSY, the rate of growth population decreases and the number of individuals that can be extracted does not increase.
  • MSY is the point where the highest rate of recruitment can occur. The highest rate of harvesting can occur at the point where the highest recruitment occurs.
What are MSY’s Shortcomings?

Very basically, the major challenges to MSY’s use as a management target include:

  • It puts fish populations at too much risk;
  • It does not account for variability in population productivity (loss of habitat);
  • It does not account for species other than the target species;
  • It considers only the benefits, not the costs, of harvest; and
  • It is too sensitive to political pressure.

Mike Urch’s story (MSY not ideal solution for fisheries management) quoted academic Professor Sidney Holt who was speaking at Fishmongers’ Hall in London on the theme “Why, or why not, maximum sustainable yield (MSY)? Contemporary thoughts on the rational management of fisheries”:

“Fisheries should be managed so that they are profitable, otherwise fishermen won’t go out to fish. And fishing for maximum sustainable yield (MSY), which is a main criterion of the EU’s revised Common Fisheries Policy (CFP), is not the best way to achieve this objective. The value of the catch has to be more than the cost of catching it. Setting TACs (total allowable catches) is the worst possible way to manage a fishery.

You don’t just use the brakes when driving a car. You have to manage the input not the output, which depends on recruitment [to the fishery].” The recruitment number can be the most variable. It can change by a factor of 100 year to year.”

According to Holt:

Maximizing yields using surplus production models is an unscientific method of managing fish populations.

“You can’t use it to take account of selectivity. You’re catching too many fish when they’re young. This is the issue. You’ve got to look at the relationship between growth and death. How much more [death] is caused by fishing than nature?”

Ian Boyd, who preceded Holt as Buckland Professor for 2012/13, and spoke after him, agreed that there is little justification for the maximization of yield approach.

“Fishing for MSY also ignores fundamental aspects of the ecosystem such as the need to leave enough fish in the sea for other parts of the food chain including mammals and seabirds. To do this means reducing the proportion of the fish stocks that is harvested. 

If MSY is to be used then make it a limit not a target.” 

The Real Issue: Overcapacity in Europe

However the article revealed that it it wasn’t actually acknowledging the ins and outs of MSY at all, when both speakers both them moved to the REAL issue the inability for the European fisheries managers to effectively manage European fisheries given the over-capacity.

What gave this away was the suggestion from a [european]delegate that to achieve maximum economic yield in a fishery that was completely unregulated would mean reducing fishing effort by a massive 80 percent

Both speakers agreed that fishing in European waters should be reduced. Less fishing effort would mean more profit for those left in the fishery, and it would also provide a better balance between the components of the food chain that are harvested by fishermen, mammals and birds.

This size of reduction would not be necessary for fisheries regulated by the current CFP [common fisheries policy]. However, because of the practice of discarding, scientists — and therefore fisheries ministers — didn’t know how much fish was already being harvested, which would be necessary before a reduction in fishing effort could take place.  “We don’t know what is caught in the North Sea as 45 percent of the total catch is thrown away (discards) without being recorded.”

The article then [and by now not suprisingly] instead of debating the applicability of MSY and offering robust alternatives to MSY started mooting the applicability of input controls, where a discard ban — another objective of the revised CFP — was discussed. It was acknowledged that there were very few fishermen in the audience and that not all are thought to agree with this approach. It was also mentioned that there was a better understanding of fisheries management in the Netherlands because fishermen and scientists work better together there.”

One trustee of the Buckland Foundation [Colin Bannister] summed up:

“Fisherman have a great deal of knowledge that is worth tapping into. The ideals of fisheries management are relatively simple but the practice is actually very difficult.”

Huh? I thought that this article was discussing the efficacy of MSY as a solution?


What’s my Point?

My point is this, sadly yet again… as seems to be too often the case in fisheries management, what could be valid criticism is nothing but a case of the emperor’s new clothes!  A misdirection! A statement that states nothing!

Just when I thought that there might be an alternative on offer that could pose as a rival to the MSY paradigm, I find that it is fizzle! To use a colourful South African phrase, the article although initially promising was all “fart and no poo!”

This article didn’t do what the title (MSY not ideal solution for fisheries management) said it would do at all… It didn’t establish the inefficacy of managing to BMSY at all! Essentially it highlight the problems that beset fisheries management in Europe, and then apportioned the blame to management to BMSY.

What is most comical about this article is that, although it began well and truly discussing the merits on MSY, it ended attesting to the need to collaborate more with fishermen! The latter theme having nothing to do with the former.

In its conclusion with respect to the applicability of MSY, the article quoted Colin Bannister:

“Scientific advice for the crisis stocks is now aiming to establish a fishing rate rather than a stock biomass […] Fishing rates are now falling in the most critical fisheries, and are closer to MSY, which even though not the ideal is nevertheless a step on the way to the profitability that [Professor Holt] is seeking.”

I am not sure what Prof. Holt is after here? Is he advocating a move away from the maximum sustainable yield to optimum sustainable yield (OSY) [optimum sustainable yield is the level of effort (LOE) that maximizes the difference between total revenue and total cost]? If he is why didn’t he say that rather than wibbling about effort reductions, discard bans and improved collaboration with fishermen.

My question is this, how is the optimum sustainable yield more effective when it assumes that corresponding fishing effort is lower than that of maximum sustainable yield? Furthermore how can something delivered in an economic context [ the largest economical yield of a renewable resource achievable over a long time period without decreasing the ability of the population or its environment to support the continuation of this level of yield], be effective at managing something that is driven by by biology?

I am not convinced. 

For some good information on the optimum sustainable yield I recommend reading the 1977 article by Canadian Scientist P Larkin [An Epitaph for the Concept of Maximum Sustained Yield].

I want to explore this maximum sustainable yield versus optimum sustainable yield debate more. It is very interesting.

Managing at or above BMSY, at least from from a New Zealand perspective, seems to be working pretty well. However teh concept cannot be applied in its raw 1935 format ; it does require tweaking!  In New Zealand  as far as I can deduce from the approach taken with fisheries like rock lobster and even hoki… The management target for these fisheries is set to be at or above BMSY which is consistent with the Fisheries Act while taking into account and providing allowances for variable recruitment. These allowances are extra fish in the water on top of BMSY. These extra fish provide  a buffer to guard against low rates of recruitment…

If you look at how they manage hoki for instance, while BMSY is in the vicinity of 24-25%B0, that management target range is 35-50% B0. This target range although above is not an application of OSY, rather it is an application of MSY complete with belts and braces!


2 thoughts on “Maximum Sustainable Yield (MSY): Are we MSY-ing something?

  1. Pingback: New Zealand Fisheries: Most fish stocks in a healthy state! | Green Fish Blue Fish

  2. Pingback: Advocating a sustainable aquatic environment, sustainable marine resource use, and the reclamation of a ‘middle way’: Green Fish Blue Fish | A Soapbox: | oceanNRG

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