Weevil

Best answer as chosen by Asker / Ratings
While you're in the Pirates' Fortress getting the Hookshot (and getting the Zora Eggs), take a photo of one of the pirates (I think only her face). Then take it to the fisherman in his hut to get the seahorse.
Release the seahorse in the murky water and it will lead you to the lair of the sea snakes. Kill all the snakes (stand close to the side of the tunnels and use your cutters when they come out) and retrieve the remaining Zora Eggs in the tunnels.
Take the 7 Zora Eggs back to the lab to learn a new song. Play this song near Lulu, then use the Hookshot on a palm tree to get to the Water Temple.