Welcome to TONMO, the premier cephalopod interest community. Founded in 2000, we have built a large community of experts, hobbyists and enthusiasts, some of whom come together when we host our biennial conference. To join in on the fun, sign up - it's free! You can also become a Supporter for just $50/year to remove all ads and gain access to our Supporters forum. Follow us on Twitter and Facebook for more cephy goodness.
Five Hundred METERS? Dude, that's a quarter of a mile!
What octopus were you chasing, and are you sure it wasn't hooked by a boat?
The answer to the question of course depends greatly on the species of octopus in question, but let's assume it's a shallow water coastal vulgaris or smaller.
In the field, octos jet for two reasons: escape and just to swim, the latter being reasonably rare, and the former being rather common. Generally a panic jet from an octopus would also be accompanied by the traditional distracting cloud of ink. In that case, it's common for the octopus to only move 3-8 feet and then land, instantly blending with the surroundings, banking on it's incredible camoflauge to save the day. And it works pretty darn well- the trick is to look for the eyeballs.
When swimming along, octopuses can keep jetting for quite a while, possibly numbering up to a hundred feet or so. It's not in the best interest for an octopus to jet-swim; everything that likes to eat it can swim a heck of a lot faster than it can jet.
Squid, on the other hand, are natural born jetters. Little topedoes of the deep, it's amazing anything can actually eat squid. In a bonaire research trip, we observed caribbean reef squid jet a hundred or more feet in one go during predator-induced flight behaviors. What's truly amazing was that:
a) they did it in an eyeblink. It appeared to us to be more like teleporting.
b) they maintained their formation perfectly.
c) they did it about 20 seconds before the predators showed up.
As for C) it was so amazing that I wanted to launch a whole study to examine squid sensory apparatus. It's too easy to say they're just Strong in The Force and can detect approaching bonefish well before they arrive.
As a closing note, it's pretty funny to see your captive octopus jet across it's tank and smack the glass. You can just hear the bicycle horn-like HONK sound in your head when it happens.