MSY (the theory of Maximum Sustainable Yield) has been described as “a perfect example of pseudo science with little empirical or sound theoretical basis” by Dr Sidney Holt, co-author in 1957 with Dr R.J.H. Beverton of On the Dynamics of Exploited Fish Populations.[i] Yet, despite deepening reservations, the concept continues to gather prestige and occupy an increasingly significant role in fisheries management or, more accurately, a public relations function favouring perception of the Common Fisheries Policy. Regulating fisheries to the vague and erratic goals of MSY is now official EU policy and it is being extended beyond fish stocks to other aspects of environmental management. There are reasons for this: MSY consoles because it identifies “recovery targets” (F~msy) whose attainment is reported in optimistic terms. The targets are spurious but they are poorly understood by many environmental NGOs which agitate to reduce over-fishing. Their enthusiasm does not stretch to seeking the truth behind official reassurance to ascertain what the adoption of MSY has actually secured in terms of fish biomass recovery.

The usual manner of presenting information on MSY is by numbers of stocks (the latest exercise from the Scientific, Technical and Economic Committee for Fisheries (STECF is an example[ii]). However this approach is misleading for reasons that are further explained below. MSY concerns yield so it would be more sensible and appropriate to use a quantitative rather than a qualitative measure (such as spawning stock biomass, TAC or landings) of achievement.


Although the concept was enunciated in 1933 and adopted by the European Union in 2002, fish stock biomass has declined throughout its history. To demonstrate what has occurred in recent years this post examines fish stocks exploited by the Irish fleet. Hopefully, the exercise will be repeated in other member states of the European Union.

The justification for using Fmsy is to stabilise stocks by reducing fishing mortality (F); this is reckoned to be controllable whereas regulation of biomass is considered to be outside management possibilities. The following analysis is based on five years of Ireland’s Marine Institute data as reported in its annual Stock Book’s summary Table on fishing opportunities for the following year[iii]. The place to begin is the total number of stocks at F~Fmsy. As can be seen, there has been no dramatic trend in the number of “stocks” achieving F~Fmsy over the five years for which information is available (Fig 1). Throughout they are in a minority.Figs 1 & 2 jpcut

Its original stated purpose was for Fmsy to

 maintain or restore stocks to levels that can produce the maximum sustainable yield with the aim of achieving these goals for depleted stocks on an urgent basis and where possible not later than 2015 (subsequently extended to 2020 and “as far as possible”, just in case that was not realisable)

The implication in this statement is that, once reached, Fmsy is retained but this is clearly not what happens. Stocks which reach Fmsy may lose it the year after so that, although there is an apparent stability when stocks are expressed as total numbers, individual stocks may join and leave that category in any year. Thus, reporting stock numbers at Fmsy gives a false sense that a conservation objective has been attained.

Recording the msy status of stocks is misleading for another reason. Pelagic stocks are usually considerably larger than demersal ones and the addition or subtraction of one of these from the total is an inadequate expression of what has happened. Instead, each category, demersal, pelagic and shellfish should be considered separately.

Some more quantitative account to consider the consequences for stocks of the claims made for Fmsy would be appropriate. Ideally expressing the results in terms of biomass would be the ideal and the most suitable indicator of this would be Spawning Stock Biomass but such data are not sufficiently available. Landings might be substituted as a proxy – or the criterion could be scientific advices on TACs. Landings to Ireland are of particular interest to me. The important point is that number of stocks is insufficient; some kind of quantitative account is required. To explore this I have assumed that the landings recorded on the Marine Institute’s summary Table in, say 2014. As can be seen, the situation could be described as chaotic but certainly not as “sustainable”. We begin with a tonnage of some 173,000 t at F~Fmsy in 2010 and conclude in 2014 with 68,000 t landed at that level (Fig 2).


Figs 3 & 4 jscutNow, let’s examine those species-categories that make up the totals. Over five years the number of Demersal stocks at F~Fmsy did not alter appreciably (Fig 3), although the status of individual stocks often changed. Landings at F~Fmsy initially increased but then levelled off and they remain a small proportion (approximately 26% of the total, overall) (Fig 4).

The status of pelagic stocks varied more erratically from one year to another, a likely reflection of their smaller number. A positive trend in the number of pelagic stocks at F~Fmsy might be discerned (Fig 5) but the landings were very variable, notably in 2011 and 2012 when landings to Ireland were not recorded from some stocks whose F>Fmsy (Fig 6).

Fifs 5 & 6 jpcutShellfish stocks, Nephrops, are few. There is little or no consistent success at establishing F~Fmsy among them (Fig 7). The landings at different or no level of Fmsy display even greater variability (Fig 8).


Quota species account for some 90% by volume of “fish” landings to Ireland. Because of the inter-relationship of various fisheries and the generality of unselective towed gears, it might be expected that a reduction in F, applied to certain species, would have consequences for many. There is no evidence that this has occurred.

I conclude that the principal benefit of Fmsy is to reassure the public – and many scientists who do not understand it – that “something is being done”. I think we should expect science to tell us the unvarnished truth rather than cloaking bad news in “magic formulae” such as MSY.

One final point which I think will gain greater currency is the fact that attaining F~Fmsy is regarded as an achievement, as is suggested by the statement originating in the Johannesburg Convention in 2002. The fact that a depleted and endangered species like spurdog had this status in 2014 should give cause to re-evaluate current objectives.

1 January 2016


[i]  Maximum Sustainable Yield: The Worst Idea in Fisheries Management. Guest blog by Dr Sidney Holt Consulted on 29 December 2015

[ii] Monitoring the performance of the Common Fisheries Policy Edited by Norman Graham, John Casey and Hendrick Doerner. JRC Scientific and Policy Reports, March 2015. Consulted on 29 December 2015.

[iii] The Stock Book published by Ireland’s Marine Institute generally in November, summarises advice on the exploitation of quota species in the following year. It is available on the Marine Institute website,