Early in the 8th anniversary month (mid-March) I went to farm some shark meat in Ocean of Tears and there were no sharks to be found! Later, after the 5th anniversary quest-givers got added in during the latter part of the 8th anniversary month, I went back to OOT and found there are still no "a shark" or "a reef shark", but just "an old shark" in the locations formerly occupied by those two mobs (i.e., deep water and shallow water, respectively). An old shark seems to drop all the things that either of the previous sharks used to drop, plus the collectors item for the scavenger hunt.
I don't remember if the original 5th anniversary hunt used a replacement mob like this. I assume not or the mob would've already been in the bestiary. I have no idea why the replacement mob got used this time around.
Edit to add that, even though the anniversary hunts are over again, OOT still just has "an old shark" everywhere that used to have "a shark" or "a reef shark" (and those mobs still aren't around). I'm still not sure why they got changed, but it doesn't look like they'll be changing back.
Edited, Apr 23rd 2007 3:51am by Sukrasisx