boydski:Hi Bob,
The largest Sixgill ever recorderd off our coast was about 16' long. I wrote an article about Sixgills earlier this year, and although I ran across the 20' length during my research for the article, I could find no scientific reference to support it. Not that I could actually tell the difference between a 16' and a 20' shark mind you.
The only effective way to tell the sex of the shark is to look for claspers, or bite marks near the gills (the males bite the females as part of mating), but you knew that. All the Sixgills I've seen so far have been female.
Wow boydski, thanks for the great post. That video clip was exceelent!