I catch all my maps at lake tahtotl, all peisteskin. I've expanded to start getting them with BTN to work on the achievement, but it seems to take much longer because the map may not show up for a while, and when it does it may be the wrong grade. North Shards, Parata's Peace, and Lake Tohtotl should always and only spit out peisteskin.

My important question is, do you need high fishing to catch a peisteskin, or can anyone go do it?