I did a google search on 'Isle Royale +fishing' and got many, many hits. The first 2 are "Isle Royale National Park Hiking and Fishing Page" & "GORP - Isle Royale National Park, Michigan".
I haven't been there, but my brother went to school at Michigan Tech, and I believe he did go there. One thing I remember is that you MUST take a water purifier. Lots of nasty critters in the water on the island. Hope this helps.

Mike