“And of every living thing of all flesh, two of every sort shalt thou bring into the ark, to keep them alive with thee; they shall be male and female.”
In the book Noah’s Ark: a Feasibility Study, author John Woodmorappe suggests that, at most, 16,000 animals were all that were needed to preserve the created kinds that God brought into the Ark.
God didn’t command that the Ark carry every kind of animal. It carried only air-breathing, land-dwelling animals, creeping things, and birds. Insects and many amphibious creatures could survive in sufficient numbers outside the Ark. Also aquatic animals didn’t need to be on Ark, they had plenty of water outside. This significantly reduces the number of animals that needed to be on board.
Another factor that greatly cuts down on the space requirements, is the tremendous variety in species we see today did not exist in the days of Noah. Only the parent “kinds” of these species were required to be on board in order to repopulate the earth. For example, only two dogs were needed to give rise to all the dog species that exist today.
Creationist estimates for the minimum number of animals that would have been necessary to come on board the Ark have ranged from 16,000 to 35,000.