By Ken Ham and Tim Lovett, Answers in Genesis
In the book Noah’s Ark: A Feasibility Study, creationist researcher 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. The Ark did not need to carry every kind of animal…nor did God command it. It carried only air-breathing, land-dwelling animals, creeping things, and winged animals such as birds (Gen. 7:14,15). Aquatic life (fish, whales, etc.), insects, and many amphibious creatures could have survived in sufficient numbers outside the Ark. This cuts down significantly on the total number of animals that needed to be on board.
Genesis 7:14 they and every beast after its kind, all cattle after their kind, every creeping thing that creeps on the earth after its kind, and every bird after its kind, every bird of every sort. 15And they went into the ark to Noah, two by two, of all flesh in which is the breath of life.