"Biological Surplus" is a scientific name for the number of animals in a given population that are "above" the carrying capacity.
For example, if there are 25 deer in a habitat that has a carrying capacity of 25, and 12 fawns are born and 2 adults die of natural causes, then the new population is 25 + 12 - 2 = 35. However, since the carrying capacity of the habitat has not changed, there will be 10 deer that will not be able to survive in this habitat. They will either move to other areas or will die of starvation, disease, predators or hunting. These 10 deer are the biological surplus–the "extra" animals that can be removed without changing the overall population.
Most game animals have a high biological surplus, and these surplus animals can be removed without affecting the population. In fact, if they are not removed by hunting, most will die anyway due to other causes (disease, starvation, roadkill, etc.).
If animals are being harvested or dying faster than they can be replaced, the number of breeding animals will be reduced, and the herd or flock will not be able to sustain its numbers.
It's important to have enough mature animals to produce new, young animals each year. It's also important to have enough young animals to replace the mature animals as they die off. Breeding stock is the correct mixture of adult and young animals needed to sustain a healthy population.
Wildlife managers must ensure that enough breeding
stock survives to produce a new crop of wildlife each spring. In order
to accomplish that, wildlife managers must assess how many animals are
"surplus" to each game population and protect the remainder.
Hunting seasons, bag limits and license quotas are tools that wildlife
managers use to protect breeding stock.