To obtain the Sinker Lure you must first catch a Hylain Pike, Hyrule Bass, and a Ordon Catfish in the fishing hole area with the lure rod. After you have caught one of each you go to the south east corner of the water closest to the house and take out your Fishing Rod(bobber). After that you will catch the Sinker Lure. Make sure Hena doesn't see you use it or she will take it away.