My theory is that you need at least level 98 base fishing skill in order to catch these, have obtained the Key Item "Angler's Almanac" for 20,000 GP from the guild NPC, and have "activated" the Expert "quest" from the NPC that promotes you to a higher rank (i.e. have the NPC tell you to catch the Tiger Shark).
Good bite rate? I've been fishing this for 3 hours on the boat both ways with slices of Carp and have not got a single bite. No bite in 3 hours is a HORRIBLE bite rate.
