A stock objection to the flood account is that a single breeding pair of each animal would be insufficient to repopulate the planet. They wouldn't multiply fast enough. The gene pool would be too depleted. And the species would become extinct if either the male or female was killed soon after they disembarked.
A few quick observations:
i) Actually, Genesis says there were seven breeding pairs of clean animals. The narrator uses the synoptic/resumptive-expansive compositional technique, by introducing a general statement, then revisiting that theme in greater detail.
ii) This objection poses a challenge for the global flood interpretation, not the local flood interpretation.
iii) But assuming the global flood interpretation, what if pregnant animals were taken aboard? Females impregnated by a different male than the male on the ark.
That would greatly augment the sample leaving the ark, as well as deepening the gene pool. Nothing in the text restricts the female animals to virginal specimens or specimens that were not pregnant at the time.