You can put his exact question into a search engine, and it will give you the answer.

Fascinating reason, isn't it? :)

My daughter had an interesting question once: how do mermaids avoid this?

It's because he's an "English Teacher"

http://www.italki.com/question/327216

So he wants to make sure everyone can admire his fine handle on the English language. 

Wrinkles induced by water indicate that wrinkles are instead produced by the nerves that automatically trigger the decrease of the blood vessels under the skin, which reduces the volume of tissue.