Quick notes on Sustainable Yield

Sustainable Yield (SY) refers to the increase in natural capital. It is the natural income that can be exploited each year without depleting the original stock or affecting its potential for replenishment.

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.

However, there is a convenient formula for calculating Sustainable Yield:

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

Economy and Systems

An economic system produces and distributes goods and services by using natural, human and manufactured resources. It works just like an environmental system: it is made up of certain components, require inputs (resources) and produces outputs (good and services).

Economic systems seek to satisfy people's needs and wants in the most efficient and effective way. The success or failure of an economic system is based on how efficiently and effectively it carries out its activities. An economic system is also in charge of the distribution of wealth.

As in any system, there needs to be an input of resources. In an economic system, these resources are known as capital, and it is used to produce goods and services.

Capital can be divided into three categories:

1. Natural Capital
2. Human Capital
3. Manufactured Capital

Natural capital and natural income include natural resources that have value. These are resources that support life. Examples include trees, soil, water, living organisms, etc. Natural capital also includes processes such as photosynthesis and biogeochemical cycles, because these help promote life.

Natural capital in economic systems is extremely important since natural capital yields natural income. In fact, the World Bank calculates a country's wealth by also considering the way it administers its natural resources, along with the other criteria.

Natural resources can be classified into 4 categories by their availability or depending on how long it takes for them to be renewed.

1. Renewable
   
2. Non-renewable
   
3. Replenishable
4. Recyclable

It is possible for a certain resource to fall into more that one category, and there may be ideas that differ depending on each person's point of view.