The good news is, even if you wear a complicated prescription (as with the bifocals, trifocals, and progressive lenses mentioned above), you won't have a hard time finding a pair of sunglasses that fit all your needs simultaneously.
You probably won't need anything this extravagant just for fishing, but it's available if you do (or if you plan to take your fishing glasses and use them for other activities for which trifocals work best).
Big frames are popular in men's sunglasses, especially for those who need bifocals, trifocals or progressives and are choosing a regular frame to put a tinted, prescription lens into.
They offer something for each walk of life, from fashion-conscious smaller frames to larger frames for ophthalmologic patients whose eyewear may require bifocals or even trifocals.
However, if you need bifocals, trifocals, progressive bifocals (especially these), it could be hard to fit your prescription into such an abbreviated frame and lens combination.