Something is up with this boss. I'm not absolutely sure that it counts and, if it does, what criteria, if any, must be met to actually count toward the achievement.

I wasn't awarded the 100 kill ap until I switched to Windmore Harbor and killed Captain Bluecrab once. I have no way of knowing whether it was just a coincidence. I no longer go to Southern Seas to farm for the AP. Windmore Harbor takes about 30 seconds longer but I'd rather be sure I'm getting credit for the kills.