Why does secondary succession occur much quicker than primary succession

It is usually faster than primary succession as: soil is already present so there is no need for pioneer species. Seeds, roots, and vegetative organs of plants may still survive in the soil.

In some developing nations the percentage of the animal protein from fish in the diet can be as high as 25 percent.  about 85% of fish caught is used for human consumption.  the remainder is converted into fishmeal and fish oil.