Question

what marks the moment of extinction? when the last individual of a species dies off when a species numbers get into double digits when the last fertile female of the species dies

Explanation:

Extinction is defined as the complete disappearance of a species. When the last individual of a species dies, there are no more members of that species left in the world. A species with double - digit numbers is still extant (alive). And even if the last fertile female dies, if there are still other individuals (e.g., non - fertile females or males), the species may still technically exist for a short while until the very last individual perishes.

Answer:

when the last individual of a species dies off