There are 5173 fish living in the ocean. 401 get eaten, 218 die by pollution and 89 drown. How many fish are in the ocean now?

By taking your riddle as it is, and without looking behind the lines, I would do a normal subtraction. The answer would be 4465 fish.

If that was wrong and they meant something else.

Well, can fish drown?

Honestly, this is the first thing that caught my attention when I read your riddle. Technically, fish do not drown. Water is their natural environment. But Something happened to them such as suffocation, lack of oxygen that makes them die and drown. So it might be acceptable to say they drown.

If that term"89 drown" was the key, then just do normal subtraction and do not subtract 89 from the total number and that would be the correct answer.