For one, the Bible says that everything on the Earth was a goner. I know. You will find reason to consider that to mean the dry land only, but that does not make much sense and is not a literal view of the Bible. It also does not explain distributions or how these organisms could have survived adverse conditions that were the same the world over according to creationists.Why would aquatic animals not survive? And why wouldn't aquatic animals gravitate to the best environment to prosper?
Terrestrial aquatic animals that exist in shallow lotic environments wouldn't stand a chance and those from lotic environments might live only marginally longer before succumbing to sediment loads, changes in salinity, pressure, temperature, depth, sunlight penetration, loss of plants for food, substrate or breeding, changes in dissolved oxygen, heavy metal toxins and on an on. You are suggesting that this flood created mountains, continents and canyons, but was somehow as gentle as a mother's caress on aquatic organisms.
I have seen the aftermath of a fairly well-known regional flood where sand and other sediment was piled 10-15 deep over hundreds of acres after the waters ebbed. That would be nothing compared to what any reasonable person would expect if the globe had been flooded.
It was pretty cool to drive through after heavy equipment had cut back down to where the old roads were buried.
As far as going where they will prosper you will have to tell me, I did not mention anything about that. Unless you think that endemic species somehow congregated in deep, darkened flood waters over areas of the world that they guessed would be good for them when the flood retreated? You will have to explain it.
Why are the aborigines of Australia very like the Indians in South America and the natives of Hawaii? and how did they get there?Based on the evidence, Australia was first colonized 65,000 years ago. What do you mean very like these other groups? Do you mean they share an origin or that they happen to look alike for unspecified reasons and you want that to be because of a flood, but really you have no idea?
I have no idea. Are the similarities based on anything real or are they just superficial? The natives of North and South America share an origin and that can be traced back 15,000 years or more to tribes that crossed the Bering Strait land bridge. There is no indication that the Australians share that genetic heritage and they are more closely related to people of New Guinea and the Philippines.
If you find anything that links these peoples in heritage, origin and time, bring it here explain why you brought it up and how that might support a global flood. As it stands, it appears to be superficial similarities.