Natural mortality includes non-human predation, disease and old age.

The equation assumes that fishing and natural mortality occur simultaneously and thus compete with each other.

There are a large number of natural mortality agents which could be responsible for population cycling, including parasitoids, predators, starvation, disease, and severe weather.

This change in currents raises sea surface temperatures, reducing food supplies and so increasing natural mortality.

There are two basic approaches used to estimate natural mortality: tagging studies and growth parameters.