Your question presupposes the literal historicity of the story of Noah’s ark found in Genesis 6-8. Although the story was assumed to be literal for hundreds of years, since about the 19th century mainline scripture scholars have rejected a literal interpretation of this story. (In fact, hundreds of ancient cultures recorded stories of a great flood, and some of these were written before our biblical account.) Even though some people continue to search present-day Turkey for remnants of the ark, Catholic teaching since Vatican II instructs us that the Bible is not to be read without taking into account particular literary genres. For example, we are not to read mythological stories, such as this one, as historically factual. (Note that “mythological” isn’t a derogatory term here – it simply refers to a literary genre.) As Catholic biblical scholar Raymond Brown points out, “Some of the most serious mistakes of biblical interpretation have flowed from an assumption, quite unwarranted, that all the books of the Bible are history.” The Catholic Church holds that the story of Noah (as well as the rest of the Bible) is true—revealing insights into our relationship with God—but not necessarily historically factual.
So what is the truth of the Noah story? God is compassion and works saving grace for a sinful humanity.