I should assume you're playing on pc, because i am not aware of this issue happening on andoird or ios. The issue with sharks covers only the pc side of it, if the shark is directly facing your way they will not be able to grab the bait. The only way to go with them is if they bite it while they're facing 45 degrees away from your direction. Say you're player is east the shark will have to bite the bait while facing south, west, or north for it to work. If that is not the case then it will not work. Again, i do not know if this issue has moved on to Ios/android devices but the last time i was into fishing, this was only happening in the pc version (facebook client).