If you see it as a business, you could consider sustainable yield as the 'retained profit' of a company. It is the amount that one has left over and can use to invest in other aspects of the business. That money can be used to expand and grow or to improve the business in any other way. It is the same with Sustainable Yield, that increase in natural capital is what is available for use and would not affect the environment. It is like the money a company can use to make itself better without going into debt.
* MSY means the maximum sustainable yield, and it is the one that is of interest commercially speaking.
Some important aspects to consider when calculating sustainable yield are:
- carrying capacity
- population size
- total biomass or energy at a given time
- Rates of change of population, biomass, and energy.
SY= Annual Growth and Recruitment - Annual Death and Emigration
Basically, what this calculates is how many organisms are there at a given point in time. It considers new individuals that came in, and individuals that died or left.
Sustainable Yield can also be calculated by
SY= (Total Biomass or energy at a Time T)+1 - (Total Biomass or energy at a Time T)
This is useful when calculating the changes in SY over a period of time. It would be used when comparing biomass in 2009 and biomass in 2010.
Here is an example on how sustainable yield is important for economic systems. It is a report on the commercial value of estuaries in Australia.
http://www.ozcoasts.org.au/indicators/econ_value_commercial_fisheries.jsp
Also, here is an ecological assessment of rivers and estuaries (also in Australia). This is the type of information that is useful when evaluating an ecosystem and its natural resources.
http://www.anra.gov.au/topics/coasts/pubs/estuary_assessment/est_ass_int_wpdd.html
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