@Darkstorm:
Not really what I was saying. If the Kraken's strength is sufficient to defend FI, then in the past the strength of the fishmen should have been sufficient to protect it from slavers without the necessity of Newgate's protection.
Just because Luffy knocked it out doesn't mean that any old Fishman-level fighter could do the same, or that Surume isn't a force that could be used to protect Fishman Island. Arlong was a better than average Fishman and Luffy was able to take him down before he even went into the Grand Line. Compare that Luffy with the Luffy we have now and they're not even in the same league. The Kraken is weaker than the Monster Trio, but that doesn't make him weak compared to rookie pirates coming in from Sabaody.
Luffy's name is infamous enough at this point that it alone could be used as a deterrent. If you put a Kraken right next to his territory and warn everybody that you'll be on Straw Hat's bad-side if you do anything to the people he protects then that might be enough to deter people from attacking anything.
It doesn't even look like Whitebeard had any protectors on the islands that were under his control, which is shown when everybody goes rampaging through his territories after he dies. The only thing keeping people from attack his territories was "the threat of Whitebeard". I know that Luffy isn't on Whitebeard's level yet, and that "the threat of Straw Hat" isn't very well known compared to somebody of Yonkou status, but that's what the Kraken is for; to back up his word, and insurance policy.
Of course this is all still theory though, just something I could see logically happening. It makes perfect sense to me. Can you really see Surume pulling Sunny to islands from now until the end of the series? I can't. Him sitting at shore from now on would be a waste in my opinion.