I had a hard time with that part too, make sure the cat is there when you are talking to the fisherman, and you should see it when you walk back to the crates, but then he will go around them once ( if I remeber correctly ) and walk past again on the left where you enter between the crates, I beleive I clicked on him then and finally got it. I dont know how many times I had to try before I could get it but it was ALOT!
Good Luck!