Fishing poles function as a [d6 2h] improvised weapon which breaks on max damage; the d8 is meant to be when used as a single-shot hunting rifle - the d4 is the usage of it as a standard fishing pole for the purposes of angling.
So the Gentleman's Rod would be as a weapon the following:
Gentleman's Rod d6 improvised (break on max damage) or d8 single shot (as Hunting rifle).
- d4 Angling.
I could've written it better; and certainly will figure out how to finagle it out should I expand upon it.
Thanks for asking! Hope that helps.