Ok so I'm leveling fisher with the Namazu and the quest "beat of the drum" seems to have a little bit of a misleading quest description. It says to catch a leatherscale in the "upper Yat Khaal" but when I searched the river there was no indicator that the proper node was found.
Instead I looked it up online and it seems that the fish is actually located in the lower "Tao Khaal" The quest description should probably be fixed.