Why Is It Important To Know About Maximum Sustainable Yield (MSY) ?
Why Is It Important To Know About Maximum Sustainable Yield (MSY) ?
Why Is It Important To Know About Maximum Sustainable Yield (MSY) ?
April 2012
What is MSY?
In population ecology and economics, MSY is the largest average yield (catch) that can theoretically be
taken from a species stock over an indefinite period under constant environmental conditions. It is
usually measured in tonnes. To have a viable and thriving fishing sector, the size of fish stocks must be
above levels where they can produce the maximum sustainable yield over an indefinite timeframe.
B: Biomass is simply the body-weight of all the fish of one specific stock in the water. B does not
differentiate age, gender etc. It is measured in tonnes.
Y: Yield is the catch, i.e. the fish taken out of the water through fishing. It is measured in tonnes.
MSY: Maximum sustainable yield is, theoretically, the largest yield (catch) that can be taken from a
specific fish stock over an indefinite period under constant environmental conditions. It is
measured in tonnes.
F: F is the fishing mortality rate i.e. the catch relative to the size of the stock (the proportion of fish
caught and removed by fishing).
BMSY: BMSY is the biomass that enables a fish stock to deliver the maximum sustainable yield. In theory,
BMSY is the population size at the point of maximum growth rate. The surplus biomass that is
produced by the population at BMSY is the maximum sustainable yield that can be harvested
without reducing the population.
FMSY: FMSY is the maximum rate of fishing mortality (the proportion of a fish stock caught and removed
by fishing) resulting eventually, usually a very long time frame, in a population size of BMSY. FMSY
is a constant and can be applied to any stock that is not impaired in its reproductive capacity.
MEY: The maximum economic yield (MEY) is the value of the largest positive difference between total
revenues and total costs of fishing (including the cost of labour and capital). MEY is typically
achieved at catches that are 10-20% smaller than MSY.
FMEY: FMEY is the fishing mortality (the proportion of fish caught and removed by fishing) resulting in
MEY. FMEY is typically 10-20% smaller than FMSY.
MSY, BMSY and FMSY, as well as MEY, BMEY and, FMEY are reference points which are expected to remain
fixed unless the environment changes or better data become available. Conversely B, Y and F may
change every year, and in the EU context are also corrected retroactively (backwards in time) by the
International Council for the Exploration of the Seas (ICES).
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However, depending on the fishery, the time needed until catches first regain and then exceed previous
levels can be only a few years. Without action to stop overfishing, a stock could collapse with deeper
and longer-term impacts on both the fishing sector and the marine environment.
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What about data deficient stocks?
The majority of the stocks fished in EU waters are currently assessed as 'data-poor'. However, there are
NO biological or scientific reasons why fishing pressure in 2015 cannot be at rates below FMSY or below a
proxy in the case of data-poor stocks. Australia, New Zealand and the USA use proxies for MSY and
historic catch levels for data-poor stocks.