Sustainable Yield

I liked a lot the notes taken from Ada's Blog "The first law of Ecology" in which the information about sustainable yield is summarized as the following:

...

"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.

* 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)