My understanding is that I am supposed to "talk" to Senator Nellek to get information from him. I have fought him 3 times and won and have not gotten anything from him. He disappears and the quest arrow points me out of the area. I leave the area and it points me back into the area to fight again. Granted it has been a loooong while since I went through this particular quest with my lvl 80 balance mage, but still...
Is this a case of keep fighting till I can "pin him down?"
Ah, Nellek. I think he sends you out to retrieve a couple of items and then he wants you to talk to a different crab, Senator Pluvious. Pluvious lets you in on some information about Nellek (don't want to spoil anything), and when you return to Nellek that's when he challenges you to a duel.
After you defeat him the quest should end immediately.
The quests for Nellek go in this order:
Helping Claw (meet Nellek for the first time) Charter Course (get his charter from Piceans) Turn of the Tide (get his Scepter of the Tides) Quick Change (talk to Senator Pluvious)
So I guess my only advice is to be sure that you checked in with Pluvious before fighting Nellek.