Ask A Scientist© Biology Archive

Question:
At what depth are giant squid normally found?
If this is in the aphotic zone, what purpose does the ink sac serve?
Have these squid been observed by man alive?
Tom F Ihde

Answer: 
1) Giant  squid are normally found from 300-600 meters
deep, but there are documented sightings down to approx. 1175 m.
2) Good question!  Yes, this is the aphotic zone, however, the
term "aphotic" refers to the fact that there is not enough light
for plants to grow, not necessarily that there is no light.
So, there could very well be enough light for the squids ink to
function as a "dummy" or decoy to confuse the predator, or as a
"smoke screen" allowing the squid to escape.  It is  also possible
that the squid's ink could function to protect the animal without
being seen...as it turns out, the ink is very alkaloid, (it has a
high pH) which may function to anesthetize the predator's sense of
smell!
There is also the possibility that the giant squid don't even have
an ink sac, which is often the case with deep-dwelling squid.
3) These animals have indeed been seen and captured while alive,
though little is known about their natural behavior (as far as I
know)
Tom F Ihde