Re: if we have never found a giant squid how do we know they are there?

Although we've never seen a living giant squid (_Architeuthis_), we've 
found plenty of dead ones. Over the past 100 years, around 200 giant squid 
have either washed ashore or been caught in fishing nets. There are even 
some on display - there's a 9 foot long female at the National Museum of 
Natural History in Washington, DC, and a 10 foot long male is at the 
American Museum of Natural History in New York.

We think that even larger giant squid exist, because we sometimes find 
sucker scars from giant squid on sperm whales (sperm whales eat giant 
squid, and the squid seem to put up a fight!). Using the scars, we've 
estimated that giant squid can get to be up to 59 feet long. 

The search is on now to find a living giant squid. This is harder than it 
sounds, because they're fast swimmers and live very deep in the ocean -- 
around 3000 feet down.